tag:theconversation.com,2011:/au/topics/asexual-reproduction-2048/articlesAsexual reproduction – The Conversation2023-10-23T12:25:17Ztag:theconversation.com,2011:article/2146902023-10-23T12:25:17Z2023-10-23T12:25:17ZBiological sex is far from binary − this college course examines the science of sex diversity in people, fungi and across the animal kingdom<figure><img src="https://images.theconversation.com/files/554094/original/file-20231016-21-1wrv5k.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2169%2C1382&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Biological sex comes in many more forms than just male or female.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/watercolour-illustration-of-male-and-female-symbols-royalty-free-image/1209433697">Yifei Fang/Moment via Getty Images</a></span></figcaption></figure><figure class="align-right ">
<img alt="Text saying: Uncommon Courses, from The Conversation" src="https://images.theconversation.com/files/499014/original/file-20221205-17-kcwec8.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/499014/original/file-20221205-17-kcwec8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499014/original/file-20221205-17-kcwec8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499014/original/file-20221205-17-kcwec8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499014/original/file-20221205-17-kcwec8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499014/original/file-20221205-17-kcwec8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499014/original/file-20221205-17-kcwec8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/topics/uncommon-courses-130908">Uncommon Courses</a> is an occasional series from The Conversation U.S. highlighting unconventional approaches to teaching.</em> </p>
<h2>Title of course:</h2>
<p>Diversity of Biological Sex Characteristics</p>
<h2>What prompted the idea for the course?</h2>
<p>Most people view biological sex, or the physical features related to reproduction, as <a href="https://www.pewresearch.org/social-trends/2022/06/28/americans-complex-views-on-gender-identity-and-transgender-issues/">simple and binary</a> – either male or female. Even those who recognize that gender – referring to cultural norms around biological sex, or a person’s internal feeling of being masculine, feminine or both – can be complex and nuanced don’t see biological sex in the same way. Many also regard variability in sex and gender as exclusive to people – not found in nonhuman animals.</p>
<p>I am a <a href="https://scholar.google.com/citations?user=OaEmJXAAAAAJ&hl=en">behavioral neurobiologist</a> who has been teaching human physiology since 1998. Over the past several years, I have <a href="https://theconversation.com/brain-scientists-havent-been-able-to-find-major-differences-between-womens-and-mens-brains-despite-over-a-century-of-searching-143516">focused my reading and writing</a> <a href="https://www.psychologytoday.com/us/blog/governing-behavior">on the biology of sex</a>. It struck me that many of my students had misguided assumptions about sex characteristics, including that all people are physically either 100% male or 100% female. </p>
<p>A <a href="https://ari.oucreate.com/4873-5873_syllabus.pdf">course on biological sexual diversity</a> in both nonhuman animals and people could challenge these assumptions.</p>
<h2>What does the course explore?</h2>
<p>First, we examine <a href="https://doi.org/10.1002/dvg.1020150303">why sexual reproduction evolved</a> in any species. This question is <a href="https://theconversation.com/why-did-sex-evolve-researchers-edge-closer-to-solving-longstanding-mystery-55407">still hotly debated among biologists</a> because sex is inefficient. It requires time and energy to find a suitable mate and unite your sex cells, plus it allows you to pass on only half your genes to your offspring.</p>
<p>In comparison, <a href="https://openstax.org/books/biology-2e/pages/32-3-asexual-reproduction">asexual reproduction</a> – essentially cloning yourself – is much more efficient. You don’t have to find a mate, and everyone can produce offspring themselves because there are no males. In biology, “male” refers to an individual that makes small sex cells like sperm, and “female” refers to an individual that makes large sex cells like eggs.</p>
<p>Next, we explore <a href="https://www.ucpress.edu/book/9780520280458/evolutions-rainbow">nonhuman sexual diversity</a>, including fungi that have <a href="https://doi.org/10.1016/j.fbr.2015.08.002">thousands of sexes</a> and aphids that <a href="https://doi.org/10.1016/S0169-5347(01)02331-X">reproduce asexually most of the year</a> but sexually once each fall. Among many others, we also learn about fish that are male or female at <a href="https://doi.org/10.1016/B978-0-12-800049-6.00160-8">different times of their lives</a>; <a href="https://doi.org/10.1016/j.isci.2020.101652">intersex crayfish</a>; and <a href="https://doi.org/10.1016/j.yhbeh.2005.07.013">female spotted hyenas</a> that have a penis.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/Jxs2yHP6K2E?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Sex characteristics manifest in different ways across the animal kingdom.</span></figcaption>
</figure>
<p>We then transition from nonhuman animals to people, via the brain. We learn about <a href="https://doi.org/10.1177/1073858419867298">a few small</a> <a href="https://doi.org/10.1007/s00359-019-01376-8">brain structures in vertebrates</a> that likely have reproductive functions and are differently sized in females versus males on average. We also learn that most people have some brain structures that are more typically male, others that are more typically female and still others that are intermediate – in other words, <a href="https://doi.org/10.1073/pnas.1509654112">most people are mosaics</a> of female-typical and male-typical brain sex characteristics.</p>
<p>Finally, we focus on the biological sex characteristics of <a href="https://doi.org/10.1038/518288a">intersex people</a>. The <a href="https://doi.org/10.1038/nrendo.2014.130">chromosomes and reproductive organs</a> of intersex people have <a href="https://www.ted.com/talks/emily_quinn_the_way_we_think_about_biological_sex_is_wrong#t-781094">some typically female and some typically male characteristics</a> or are intermediate between them.</p>
<p>Students then build on their knowledge of the diversity of biological sex characteristics to discuss whether intersex infants should have <a href="https://aeon.co/essays/people-born-intersex-have-a-right-to-genital-integrity">surgery to “correct” their genitals</a>, as well as <a href="https://www.nytimes.com/2016/07/03/magazine/the-humiliating-practice-of-sex-testing-female-athletes.html">who should be allowed</a> <a href="https://doi.org/10.1080/15265161.2012.680533">to compete in</a> <a href="https://theconversation.com/striking-a-balance-between-fairness-in-competition-and-the-rights-of-transgender-athletes-159685">girls and women’s athletics</a>.</p>
<h2>Why is this course relevant now?</h2>
<p>Perhaps more than ever, there is a debate about how to treat people who do not fit neatly into a female or a male box. Many assume that biological sex is binary and regard transgender and nonbinary people as mistaken or confused. In addition, for many decades, <a href="https://theconversation.com/gender-affirming-care-has-a-long-history-in-the-us-and-not-just-for-transgender-people-201752">intersex infants</a> have undergone surgical procedures to make them appear more typically male or female. Even those who support transgender, nonbinary and intersex people often assume that biological sex is binary. But this assumption is not anchored in evidence.</p>
<h2>What will the course prepare students to do?</h2>
<p>Students often say that before they took this course, they had no idea biological sex characteristics could be so diverse, despite having taken several biology courses. </p>
<p>An improved awareness of the complexity of biological sex may help shape the research and teaching of future biologists. This will help them design experiments that take account of the diversity of their subjects and be more <a href="https://theconversation.com/trans-students-benefit-from-gender-inclusive-classrooms-research-shows-and-so-do-the-other-students-and-science-itself-204777">inclusive in their teaching</a>. It may also help all students ask better questions and make better judgments about social and political issues related to sex and gender.</p><img src="https://counter.theconversation.com/content/214690/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ari Berkowitz receives funding from the Oklahoma Center for the Advancement of Science and Technology and has received funding from the National Science Foundation and the National Institutes of Health.</span></em></p>Spanning evolutionary biology, genetics, development, neurobiology, endocrinology and psychology, as well as current events and sports, students explore the complexities of the biology of sex.Ari Berkowitz, Presidential Professor and Director of Graduate Studies, Biology; Director, Cellular & Behavioral Neurobiology Graduate Program, University of OklahomaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1842412022-06-02T20:18:46Z2022-06-02T20:18:46ZThis Australian grasshopper gave up sex 250,000 years ago and it’s doing fine<figure><img src="https://images.theconversation.com/files/466494/original/file-20220601-49050-8arffe.jpeg?ixlib=rb-1.1.0&rect=7%2C7%2C5168%2C3437&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Michael Kearney</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Most animals on Earth have two sexes, male and female, that combine and mix their genes when they reproduce. We are so accustomed to this state of affairs that the existence of all-female species that don’t have sex, but instead reproduce by cloning, comes as a great surprise.</p>
<p>The beautiful green grasshopper <em>Warramaba virgo</em> is one of these rare “parthenogenetic” species, in which an egg can develop into an embryo without being fertilised by a sperm. It lives in the southern parts of the Australian arid zone, where it feeds on mulga trees and other shrubs and bushes in the summertime.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/466495/original/file-20220601-48567-e5l8xx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A full-body photo of a Warramaba virgo grasshopper against a white background." src="https://images.theconversation.com/files/466495/original/file-20220601-48567-e5l8xx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/466495/original/file-20220601-48567-e5l8xx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/466495/original/file-20220601-48567-e5l8xx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/466495/original/file-20220601-48567-e5l8xx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/466495/original/file-20220601-48567-e5l8xx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/466495/original/file-20220601-48567-e5l8xx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/466495/original/file-20220601-48567-e5l8xx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The grasshopper <em>Warramaba virgo</em> reproduces asexually.</span>
<span class="attribution"><span class="source">Michael Kearney</span>, <span class="license">Author provided</span></span>
</figcaption>
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<p>We have studied these grasshoppers for the past 18 years to understand how they developed asexual reproduction, and how the change has affected their ability to survive and reproduce.</p>
<p>Our <a href="https://doi.org/10.1126/science.abm1072">new research published in Science</a> shows <em>W. virgo</em> arose about 250,000 years ago from a cross between two different sexually reproducing species of grasshopper, and giving up sex appears to have had no negative repercussions for them whatsoever.</p>
<h2>The puzzle of parthenogenesis</h2>
<p>Biologists studying evolution have often considered the rarity of parthenogenetic species like <em>W. virgo</em> as a major puzzle. </p>
<p>This is because sex imposes big costs on animal reproduction. First, there is the “two-fold cost of sex”: half a creature’s offspring (the males) are unable to produce their own offspring alone, so they are often seen as “evolutionary wastage”. </p>
<p>Moreover, finding a mate takes energy and mating animals are often at greater risk of attack by predators. Doing away with males also removes these drawbacks.</p>
<figure class="align-center ">
<img alt="A photograph showing a low bushy green tree in a landscape of red dirt" src="https://images.theconversation.com/files/466496/original/file-20220601-49336-m39kx3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/466496/original/file-20220601-49336-m39kx3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/466496/original/file-20220601-49336-m39kx3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/466496/original/file-20220601-49336-m39kx3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/466496/original/file-20220601-49336-m39kx3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/466496/original/file-20220601-49336-m39kx3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/466496/original/file-20220601-49336-m39kx3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"><em>Warramaba virgo</em> feeds on mulga trees (many of which also reproduce asexually).</span>
<span class="attribution"><span class="source">Michael Kearney</span>, <span class="license">Author provided</span></span>
</figcaption>
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<p>So why does sex exist at all? The main reason, biologists think, relates to the mixing or “recombination” of genes as a consequence of sex. This can speed up the rate of adaptation by bringing favourable combinations of genes together and also helps to purge a population of combinations of bad mutations. </p>
<p>Parthenogenetic species don’t have these processes: instead, all members of the species have virtually identical genes. This means they might be less able to adapt when the environment changes. What’s more, parthenogens could accumulate bad mutations that reduce their fitness.</p>
<p>But are these costs real? Do they result in the rapid extinction of any parthenogens that happen to form? </p>
<h2>What’s the secret of W. virgo?</h2>
<p>Over the past 18 years we have been investigating these questions in <em>W. virgo</em>. </p>
<p>This grasshopper was first studied in 1962 by the eminent evolutionary biologist and geneticist <a href="https://www.science.org.au/fellowship/fellows/biographical-memoirs/michael-james-denham-white-1910-1983">Michael White</a>. White’s young son Nicholas first discovered them near the New South Wales town of Hillston, when he noted that only females of a particular species could be found. </p>
<p>White then went on to show that the same species was present 2,000 km away in Western Australia, along with a sexual species (recently named <em>W. whitei</em>). </p>
<p><em>W. virgo</em> turned out to have a hybrid origin: a cross between <em>W. whitei</em> and another species, <em>W. flavolineata</em>, many thousands of years in the past.</p>
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<figcaption>
<span class="caption"><em>Warramaba virgo</em> (middle) and its ‘parent species’, <em>W. flavolineata</em> (left) and <em>W. whitei</em> (right)</span>
<span class="attribution"><span class="source">Michael Kearney</span>, <span class="license">Author provided</span></span>
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</figure>
<p>A parthenogenetic species might have an advantage if its genetic diversity is boosted by repeated hybridisations between the two parent species, producing an army of different clones. Combining the genomes of the two species might also make the parthenogens more vigorous.</p>
<p>Such “hybrid vigour” does occur in some animals, such as mules (crosses between a horse and a donkey). The mule has much greater strength and endurance than its parent species. </p>
<p>Could it be that the hybrid origins of <em>W. virgo</em> generated a diverse clone army with special abilities compared to its sexual relatives, or a hybrid with high level of vigour?</p>
<h2>Few benefits to giving up sex, but also no drawbacks</h2>
<p>The answers to these questions were a resounding “No”! </p>
<p>We examined more than 1,500 genetic markers in <em>W. virgo</em> and found almost no variation in the parthenogens compared with the parent species. </p>
<p>This showed clearly that only one hybrid mating between <em>W. whitei</em> and <em>W. flavolineata</em> was responsible for producing <em>W. virgo</em> in the first place. Based on the number and nature of mutations that have occurred in <em>W. virgo</em>, we estimate the mating occurred some 250,000 years ago.</p>
<p>We also showed that the parthenogen had no advantage over its parent species in a range of physiological traits including tolerance to heat and cold, rate of metabolism, how many eggs they lay, the size of their eggs, how long they take to mature and how long they live.</p>
<p>Meanwhile, <em>W. virgo</em> naturally produced twice as many female offspring as the sexual species. It retained its two-fold advantage over sexual species despite 250,000 years for low fitness mutations to accumulate in this species. </p>
<p>The conclusion from our research then is that <em>W. virgo</em> has become parthenogenic but without costs. It has also successfully spread all the way from the west side of the country to the east side, unlike its parent species.</p>
<h2>Why don’t more species give up on sex?</h2>
<p>So why then do we see sexual species everywhere despite their two-fold reproductive cost? We suspect it must be very difficult to develop parthenogenesis in the first place. </p>
<p>Indeed, we have tried experimentally crossing the same sexual species that gave rise to <em>W. virgo</em> and only created a few hybrids, none of which were able to produce offspring. The hybrid state may disturb the normal processes of egg development sufficiently to make parthenogenesis an extremely uncommon phenomenon in animals more generally.</p>
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<img alt="A photograph of a grasshopper sitting on a leaf." src="https://images.theconversation.com/files/466734/original/file-20220602-20-bpwey2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/466734/original/file-20220602-20-bpwey2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=228&fit=crop&dpr=1 600w, https://images.theconversation.com/files/466734/original/file-20220602-20-bpwey2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=228&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/466734/original/file-20220602-20-bpwey2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=228&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/466734/original/file-20220602-20-bpwey2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=286&fit=crop&dpr=1 754w, https://images.theconversation.com/files/466734/original/file-20220602-20-bpwey2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=286&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/466734/original/file-20220602-20-bpwey2.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=286&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A lab-made cross of W. whitei and W. flavolineata. She produced few eggs, none of which hatched.</span>
<span class="attribution"><span class="source">Michael Kearney</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We think future research into the paradox of sexual reproduction should focus on barriers that prevent sex from being lost, rather than only focusing on the advantages of sex.</p><img src="https://counter.theconversation.com/content/184241/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ary Hoffmann receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Michael Kearney does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Few animals have babies without sex, so biologists assumed asexual reproduction must have evolutionary drawbacks. But a self-cloning Australian grasshopper shows things might be more complicated.Michael Kearney, Professor in Ecophysiology and Evolutionary Biology, The University of MelbourneAry Hoffmann, Professor, School of BioSciences and Bio21 Institute, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1840562022-05-31T23:14:11Z2022-05-31T23:14:11ZMeet the world’s largest plant: a single seagrass clone stretching 180 km in Western Australia’s Shark Bay<figure><img src="https://images.theconversation.com/files/466144/original/file-20220531-24-oph25e.jpeg?ixlib=rb-1.1.0&rect=6%2C34%2C4594%2C3028&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Rachel Austin</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Next time you go diving or snorkelling, have a close look at those wondrously long, bright green ribbons, waving with the ebb and flow of water. They are seagrasses – marine plants which produce flowers, fruit, and seedlings annually, like their land-based relatives. </p>
<p>These underwater seagrass meadows grow in two ways: by sexual reproduction, which helps them generate new gene combinations and genetic diversity, and also by extending their rhizomes, the underground stems from which roots and shoots emerge. </p>
<p>To find out how many different individual plants are growing in a seagrass meadow, you have to test their DNA. We did this for meadows of ribbon weed seagrass called <em>Posidonia australis</em> in the shallow sun-drenched waters of the Shark Bay World Heritage Area, in Western Australia.</p>
<p>The result blew us away: <a href="https://doi.org/10.1098/rspb.2022.0538">it was all one plant</a>. One single plant has expanded over a stretch of 180 km making it the largest known plant on Earth.</p>
<p>We collected shoot samples from ten seagrass meadows from across Shark Bay, in waters where the salt levels range from normal ocean salinity to almost twice as salty. In all samples, we studied 18,000 genetic markers to show that 200 km² of ribbon weed meadows expanded from a single, colonising seedling.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/466148/original/file-20220531-24-puluwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Underwater photo showing scuba diver and some equipment with seagrass." src="https://images.theconversation.com/files/466148/original/file-20220531-24-puluwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/466148/original/file-20220531-24-puluwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=818&fit=crop&dpr=1 600w, https://images.theconversation.com/files/466148/original/file-20220531-24-puluwo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=818&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/466148/original/file-20220531-24-puluwo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=818&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/466148/original/file-20220531-24-puluwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1029&fit=crop&dpr=1 754w, https://images.theconversation.com/files/466148/original/file-20220531-24-puluwo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1029&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/466148/original/file-20220531-24-puluwo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1029&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sampling Posidonia.</span>
<span class="attribution"><span class="source">Rachel Austin</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>How did it evolve?</h2>
<p>What makes this seagrass plant unique from others, other than its enormous size, is that it has twice as many chromosomes as its relatives. This makes it what scientists call a “polyploid”.</p>
<p>Most of the time, a seagrass seedling will inherit half the genome of each of its parents. Polyploids, however, carry the entire genome of each of their parents. </p>
<p>There are many polyploid plant species, such as potatoes, canola, and bananas. In nature they often reside in places with extreme environmental conditions. </p>
<p>Polyploids are often sterile, but can continue to grow indefinitely if left undisturbed. This seagrass has done just that.</p>
<h2>How old is this plant?</h2>
<p>The sandy dunes of Shark Bay flooded some 8,500 years ago, when the sea level rose after the last ice age. Over the following millennia, the expanding seagrass meadows made shallow coastal banks and sills through creating and capturing sediment, which made the water saltier. </p>
<p>There is also a lot of light in the waters of Shark Bay, as well as low levels of nutrients and large temperature fluctuations. Despite this hostile environment, the plant has been able to thrive and adapt.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/466153/original/file-20220531-14-puluwo.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Aerial photograph showing coastline and shallow waters filled with dark seagrass meadows." src="https://images.theconversation.com/files/466153/original/file-20220531-14-puluwo.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/466153/original/file-20220531-14-puluwo.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/466153/original/file-20220531-14-puluwo.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/466153/original/file-20220531-14-puluwo.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/466153/original/file-20220531-14-puluwo.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/466153/original/file-20220531-14-puluwo.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/466153/original/file-20220531-14-puluwo.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The shallow, salty waters of Shark Bay.</span>
<span class="attribution"><span class="source">Angela Rossen</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>It is challenging to determine the exact age of a seagrass meadow, but we estimate the Shark Bay plant is around 4,500 years old, based on its size and growth rate. </p>
<p>Other huge plants have been reported in both marine and land systems, such as a <a href="https://en.wikipedia.org/wiki/Pando_(tree)">6,000-tonne quaking aspen in Utah</a>, but this seagrass appears to be the largest to date. </p>
<p>Other huge seagrass plants have also been found, including a closely related Mediterranean seagrass called <em>Posidonia oceanica</em>, which covers more than 15 km and may be around 100,000 years old.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/100-000-year-old-seagrass-could-be-the-worlds-oldest-organism-5212">100,000-year-old seagrass could be the world's oldest organism</a>
</strong>
</em>
</p>
<hr>
<h2>Why does this matter?</h2>
<p>In the summer of 2010–11, a <a href="https://theconversation.com/climate-change-threatens-western-australias-iconic-shark-bay-32428">severe heatwave</a> hit land and sea ecosystems along the Western Australian coastline.</p>
<p>Shark Bay’s seagrass meadows suffered <a href="https://doi.org/10.3389/fmars.2019.00455">widespread damage</a> in the heatwave. Yet the ribbon weed meadows have started to recover.</p>
<p>This is somewhat surprising, as this seagrass does not appear to reproduce sexually – which would normally be the best way to adapt to changing conditions.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-change-threatens-western-australias-iconic-shark-bay-32428">Climate change threatens Western Australia's iconic Shark Bay</a>
</strong>
</em>
</p>
<hr>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/466176/original/file-20220531-16-3vveuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/466176/original/file-20220531-16-3vveuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/466176/original/file-20220531-16-3vveuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=860&fit=crop&dpr=1 600w, https://images.theconversation.com/files/466176/original/file-20220531-16-3vveuv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=860&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/466176/original/file-20220531-16-3vveuv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=860&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/466176/original/file-20220531-16-3vveuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1081&fit=crop&dpr=1 754w, https://images.theconversation.com/files/466176/original/file-20220531-16-3vveuv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1081&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/466176/original/file-20220531-16-3vveuv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1081&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Flowers emerging from Posidonia australis seagrass.</span>
<span class="attribution"><span class="source">Angela Rossen</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We have observed seagrass flowers in the Shark Bay meadows, which indicates the seagrass are sexually active, but their fruits (the outcome of successful seagrass sex) <a href="http://doi.org/10.1093/aobpla/plaa038">are rarely seen</a>.</p>
<p>Our single plant may in fact be sterile. This makes its success in the variable waters of Shark Bay quite a conundrum: plants that don’t have sex tend to also have low levels of genetic diversity, which should reduce their ability to deal with changing environments. </p>
<p>However, we suspect that our seagrass in Shark Bay has genes that are extremely well-suited to its local, but variable environment, and perhaps that is why it does not need to have sex to be successful.</p>
<p>Even without successful flowering and seed production, the giant plant appears to be very resilient. It experiences a wide range of water temperatures (from 17°C to 30°C in some years) and salt levels. </p>
<p>Despite these variable conditions and the high light levels (which are typically stressful for seagrass), the plant can maintain its physiological processes and thrive. So how does it cope?</p>
<p>We hypothesize that this plant has a small number of somatic mutations (minor genetic changes that are not passed on to offspring) across its 180 km range that help it persist under local conditions. </p>
<p>However, this is just a hunch and we are tackling this hypothesis experimentally. We have set up a series of experiments in Shark Bay to really understand how the plant survives and thrives under such variable conditions.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/466151/original/file-20220531-12-iqy0fg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Underwater photo shows labelled seagrass plants on the seabed." src="https://images.theconversation.com/files/466151/original/file-20220531-12-iqy0fg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/466151/original/file-20220531-12-iqy0fg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/466151/original/file-20220531-12-iqy0fg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/466151/original/file-20220531-12-iqy0fg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/466151/original/file-20220531-12-iqy0fg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/466151/original/file-20220531-12-iqy0fg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/466151/original/file-20220531-12-iqy0fg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=509&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Transplant experiments.</span>
<span class="attribution"><span class="source">Martin Breed</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>The future of seagrass</h2>
<p>Seagrasses protect our coasts from storm damage, store large amounts of carbon, and provide habitat for a great diversity of wildlife. Conserving and also restoring seagrass meadows has a vital role in climate change mitigation and adaptation. </p>
<p>Seagrasses are not immune from climate change impacts: warming temperatures, ocean acidification and extreme weather events are a significant challenge for them. </p>
<p>However, the detailed picture we now have of the great resilience of the giant seagrass of Shark Bay provides us hope they will be around for many years to come, especially if serious action is taken on climate change.</p><img src="https://counter.theconversation.com/content/184056/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Elizabeth Sinclair receives funding from the Australian Government's National Environmental Science Program (NESP) Marine Biodiversity Hub and Australian Research Council.</span></em></p><p class="fine-print"><em><span>Gary Kendrick receives funding from the ARC, through ARC Discovery Grants, and the Australian National Environmental Science Program (NESP) Marine Biodiversity Hub</span></em></p><p class="fine-print"><em><span>Martin Breed receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Jane Edgeloe does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A single seagrass plant in Shark Bay is around 4,500 years old, covers 200 square kilometres of seabed, and thrives in harsh conditions.Elizabeth Sinclair, Senior Research Fellow, The University of Western AustraliaGary Kendrick, Winthrop Professor, Oceans Institute, The University of Western AustraliaJane Edgeloe, PhD candidate (Marine Biology), The University of Western AustraliaMartin Breed, Senior Lecturer in Biology, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1549982021-02-18T21:11:35Z2021-02-18T21:11:35ZCryptic sex: How female and unisexual animals reproduce ‘asexually’ — without males<figure><img src="https://images.theconversation.com/files/383398/original/file-20210209-17-1ig7ur9.jpg?ixlib=rb-1.1.0&rect=38%2C19%2C6451%2C3970&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Asexual reproduction can — through cell division, or meiosis — take place without the need for sperm.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>Not all species need sperm to fertilize an egg for sexual reproduction. Some species need sperm in order to induce completion of egg nucleus development, but then never use the sperm’s DNA. I describe how this self-sexual reproduction occurs in many animals, including some insects, molluscs, fish, amphibians and reptiles, but not mammals.</p>
<p>People have long understood that ejaculate is needed for human pregnancy, but did not understand much more. In the late 1600s, the Dutch scientist Antonie van Leeuwenhoek, who was one of the first microbiologists, thought <a href="https://www.smithsonianmag.com/science-nature/scientists-finally-unravel-mysteries-sperm-180963578/">his own sperm were parasites</a>.</p>
<p>For most of the 1700s and 1800s, <a href="https://www.jstor.org/stable/30053946">people thought that sperm contributed nothing more than a spark</a> to start development of an egg, although eventually decided — in a sexist fashion — that sperm contributed all the information and developmental instructions, while eggs merely provided a nutrient-rich vessel for the developing fertilized egg — zygote — and fetus.</p>
<p>In 1890, after chromosomes were seen under improved microscopes, German biologist Oscar Hertwig realized that <a href="https://embryo.asu.edu/pages/wilhelm-august-oscar-hertwig-1849-1922">egg and sperm each contributed half the normal number of chromosomes to a zygote</a>.</p>
<p>Therefore sexual reproduction has two parts: halving the normal number of chromosomes per cell nucleus, which is called meiosis, and restoring the normal number of chromosomes per nucleus, usually by combining chromosomes from an egg nucleus and a sperm nucleus, which is called fertilization.</p>
<p>But, as we will see, in many species, only meiosis is needed.</p>
<h2>Some form of sex</h2>
<p>It seems that all animals eventually need to engage in some form of sex. Human cells contain a nucleus with 46 chromosomes. When it goes through meiosis, the cells — and all its intracellular components, including the nucleus — multiply and then split, so that one cell with one nucleus and 46 chromosomes becomes four cells with four nuclei and 23 chromosomes.</p>
<p>Meiosis in all animals proceeds the same way. It starts with a duplication of all chromosomes in a cell nucleus that has the normal number of chromosomes (46 in humans) — all nuclear divisions start with a chromosomal duplication. Cryptic sex is <a href="https://doi.org/10.1002/evl3.216">how biologists refer to undetected meiosis</a>.</p>
<p>Not only do our bodies degrade as we age, but so do our chromosomes, which tatter at the edges. As far as we know, the only things that rejuvenate chromosomes and cell lineages is sex vis-à-vis meiosis or fertilization.</p>
<p>Next, <a href="http://doi.org/10.4033/iee.2011.4.3.n">this nucleus with twice the normal number of chromosomes divides those equally between two nuclei, and then divides each of these equally again, to form four nuclei</a>, each with half the normal number of chromosomes. Thus, either four egg or four sperm nuclei are formed. Egg cells contain four egg nuclei plus as many sperm nuclei as manage to get inside the egg cell. This is where things get interesting.</p>
<h2>No sperm required</h2>
<p>We often only consider one egg nucleus fusing with one sperm nucleus to form a zygote nucleus and the other nuclei are discarded. But two egg nuclei can fuse to form the zygote nucleus, with all other egg and sperm nuclei ejected or discarded, <a href="https://doi.org/10.1111/j.1095-8312.2009.01334.x">a process called gynogenesis</a>.</p>
<p>Meiosis of animal eggs usually requires a sperm cell to finish egg meiosis, but with gynogenesis, no sperm chromosomes are used in the zygote and both egg nuclei were from the same meiosis. Gynogenesis occurs in many different animals, including lots of fish, amphibians and reptiles, but not in mammals.</p>
<p>Gynogenesis can occur in other ways. With four egg nuclei per egg cell, each with half the normal number of chromosomes, and this time with no sperm, two of the four egg nuclei can fuse with one another to form a zygote. The remaining two nuclei are ejected or degraded. Alternatively, one of the four egg nuclei could spontaneously duplicate all of its chromosomes to form a viable zygote without fertilization, as <a href="https://doi.org/10.1007/s10577-018-9581-4">occurs in some fish</a> and <a href="https://doi.org/10.1159/000109628">salamanders</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/383821/original/file-20210211-17-rj0z7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="One yellow-dotted black salamander and one blue-dotted black salamander chilling on a log" src="https://images.theconversation.com/files/383821/original/file-20210211-17-rj0z7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383821/original/file-20210211-17-rj0z7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383821/original/file-20210211-17-rj0z7p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383821/original/file-20210211-17-rj0z7p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383821/original/file-20210211-17-rj0z7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383821/original/file-20210211-17-rj0z7p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383821/original/file-20210211-17-rj0z7p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some salamanders that have only one biological sex reproduce asexually.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>As another alternative, a spontaneous doubling of all chromosomes can occur just before meiosis, in which case the four egg nuclei at the end of meiosis will have the normal number of chromosomes and therefore one of them can form a zygote without fertilization. I would consider any of these gynogenetic scenarios to be cryptically self-sexual because they involve meiosis, but this is often called asexual reproduction.</p>
<p>With four egg nuclei and any number of sperm nuclei per mature egg cell, each with half the normal number of chromosomes, there are other ways to get self-sexual reproduction. Two sperm nuclei can fuse to form a normal zygote or one sperm nucleus can spontaneously duplicate all its chromosomes to form a normal zygote, with processes called androgenesis.</p>
<p>With androgenesis, all four egg nuclei are ejected or degraded, with the egg just providing a large nutritious cell to support the sperm nuclei. That resembles conceptualizations of sex from the 1800s! Compared with gynogenesis, androgenesis is extremely rare, only known from a <a href="https://doi.org/10.2307/2409646">few insects</a> and <a href="https://doi.org/10.1007/s004270050152">molluscs</a>.</p>
<p>The bottom line is that, except for mammals, asexual reproduction is quite common, but is often really self-sexual reproduction.</p><img src="https://counter.theconversation.com/content/154998/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Root Gorelick does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Perceptions about the role of sperm have changed over time, but asexual reproduction doesn’t need sperm for fertilization.Root Gorelick, Professor, Biology, Carleton UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/948462018-05-09T09:20:34Z2018-05-09T09:20:34ZWhat asexuality can teach us about sexual relationships and boundaries<figure><img src="https://images.theconversation.com/files/217305/original/file-20180502-153884-1qxi7p8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/success?u=http%3A%2F%2Fdownload.shutterstock.com%2Fgatekeeper%2FW3siZSI6MTUyNTMwMjUwMiwiYyI6Il9waG90b19zZXNzaW9uX2lkIiwiZGMiOiJpZGxfNDAwMjIwOTg5IiwiayI6InBob3RvLzQwMDIyMDk4OS9odWdlLmpwZyIsIm0iOjEsImQiOiJzaHV0dGVyc3RvY2stbWVkaWEifSwiYnhCZE1JQzRCYi96ZUhCZWR4QkF2RWhwaCtZIl0%2Fshutterstock_400220989.jpg&pi=33421636&m=400220989&src=eGDurk0YomLcSsha-Pv-Eg-1-0">shutterstock</a></span></figcaption></figure><p>There is an expectation that everyone feels sexual attraction and sexual desire and that these feelings begin in adolescence. Assumptions about sex are everywhere – most of time <a href="https://markcarrigan.net/tag/sexual-assumption/">we don’t even notice them</a>. Music videos, films, reality shows, advertising, video games, newspapers and magazines all use sexual content which supports the idea that sexuality, attraction and desire are normal. There is, however, a group of people that are challenging this sexual assumption, who identify as asexual. </p>
<p><a href="https://www.tandfonline.com/doi/abs/10.1080/00224490409552235">Asexuality was once thought of as a problem</a> which left people unable to feel sexual attraction to others. Upon the discovery that some people had little or no interest in sexual behaviour, researchers in the 1940s called this group “asexuals”, and labelled them as “<a href="http://journals.sagepub.com/doi/pdf/10.1177/1368430212442419">Group X</a>”. There was no more discussion of “Group X”, and asexuals and asexuality were lost to history, <a href="https://www.universityaffairs.ca/features/feature-article/asexuals-the-group-that-kinsey-forgot/">while studies of sexuality grew and flourished</a>. </p>
<p>Even today, asexuality still seems to be something of a mystery for many people – despite more people talking about it, and more people identifying as asexual. Asexuality is difficult for a lot of people to understand. And research shows that as a sexual identity, people have <a href="https://www.psychologytoday.com/us/blog/without-prejudice/201209/prejudice-against-group-x-asexuals">more negativity towards asexuals</a> than any other sexual minority. </p>
<h2>What is asexuality?</h2>
<p>What exactly asexuality is, is very much still being decided – with a lot of debate going on as to whether it is a <a href="https://www.lehmiller.com/blog/2016/9/7/is-asexuality-a-sexual-orientation">sexual orientation or a sexual identity</a>. There have also been discussions about whether it is a medical condition or if it should be seen as <a href="https://www.omicsonline.org/open-access/asexuality-dysfunction-or-sexual-orientation-2161-038X-1000185.php?aid=76817">a problem to be treated</a>. </p>
<p>But it seems that for many, being asexual is less about a traditional understanding of sexual attraction and behaviour, and more about being able to discuss likes and dislikes, as well as expectations and preferences in the early stages of a relationship. In this way, it is a refreshing way of being <a href="https://discoversociety.org/2014/06/03/asexual-lives-social-relationships-and-intimate-encounters/">honest and clear with potential partners</a> – and avoiding any assumptions being made about sex. Maybe because of this approach, a growing number of self-identified asexuals see <a href="https://jezebel.com/5877603/i-am-asexual-and-its-awesome">asexuality as less of a problem</a>, and more of a way of life. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/217306/original/file-20180502-153908-ipbjzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/217306/original/file-20180502-153908-ipbjzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/217306/original/file-20180502-153908-ipbjzd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/217306/original/file-20180502-153908-ipbjzd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/217306/original/file-20180502-153908-ipbjzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/217306/original/file-20180502-153908-ipbjzd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/217306/original/file-20180502-153908-ipbjzd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Asexuality is defined as a lifelong lack of sexual attraction.</span>
<span class="attribution"><a class="source" href="https://www.pexels.com/photo/adults-couple-couple-walking-grass-540531/">Pexels</a></span>
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<p>Discussions about sex and sexuality during the early stage of a relationship can make partners and potential partners more respectful towards a person’s choices and decisions. They also can reduce the potential of others making requests that may make someone uncomfortable, or which carry <a href="https://www.theguardian.com/commentisfree/2013/nov/26/victims-sexual-coercion-blind-to-crime">subtle elements of coercion</a>. </p>
<h2>Redefining boundaries</h2>
<p>In this way, then, with its need for honesty and clarity, asexuality is an insightful way of looking at sexuality, and the ways in which non-asexuals – also known as allosexuals in the asexual community – interact with others on a close and intimate level. </p>
<p>According to <a href="https://www.counsellingfoundation.org/wp-content/uploads/2017/11/Joanna-Russell-Asexuals-A-Hidden-One-Percent.-Therapy-Today-p22.-March-2016-Vol.27-Issue-2..pdf">one asexual</a>, her friends’ reactions to her “coming out” were underwhelming – mainly because it is an orientation defined by “what is not happening”. But for self-identified asexuals, there is actually a lot happening. They are exploring and articulating what feels right in the context of intimacy. They are considering different aspects of relationships and partnerships. They are talking to others about their experiences. And they are looking for people they can <a href="https://www.asexuality.org/">share a similar experience with</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/217309/original/file-20180502-153888-11ak97t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/217309/original/file-20180502-153888-11ak97t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/217309/original/file-20180502-153888-11ak97t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/217309/original/file-20180502-153888-11ak97t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/217309/original/file-20180502-153888-11ak97t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/217309/original/file-20180502-153888-11ak97t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/217309/original/file-20180502-153888-11ak97t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">It’s estimated that 1% of the world’s population is asexual.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/search?search_source=base_landing_page&language=en&searchterm=gay+couple&image_type=all">Shutterstock</a></span>
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<p>Asexuals are thinking carefully and critically about what it means to be close to someone, and in doing so, many of them have an understanding of non-sexual practices of intimacy. By doing all of this, they are developing a very unique skill set in a culture which is often considered to be over sexualised. </p>
<p>At a time when there is a growing recognition that many teenagers struggle to understand what a <a href="https://www.washingtonpost.com/news/parenting/wp/2017/05/17/how-to-teach-teens-to-have-healthy-romantic-relationships/?noredirect=on&utm_term=.bfb3a73f6222">healthy romantic relationship</a> actually looks like, asexuality gives us a new way of understanding relationships – both sexual and asexual, romantic and unromantic. And this could have a huge potential to help others understand closeness in relationships where there is an absence of sexual intimacy.</p><img src="https://counter.theconversation.com/content/94846/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Asexuality is less about a traditional understanding of sexual attraction and behaviour, and more about being able to discuss likes and dislikes in the early stages of a relationship.Catriona Jones, Senior Research Fellow in Maternal and Reproductive Health, University of HullJulie Jomeen, Professor of Midwifery and Dean in the Faculty of Health Sciences, University of HullMark Hayter, Professor of Nursing and Health Research/ Associate Dean Research, University of HullLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/569132016-04-14T20:01:08Z2016-04-14T20:01:08ZThese sex-starved creatures scavenge new genes from other pondlife<figure><img src="https://images.theconversation.com/files/118507/original/image-20160413-18093-1jdics8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The tiny rotifer has thrived for millions of years without sex.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/28594931@N03/15987678953/in/photostream/">Flickr/Specious Reasons</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Sexual reproduction is thought to be essential for mixing up genes and holding your own in the race for survival. A major embarrassment to this theory are microscopic animals called <a href="http://www.microscopy-uk.org.uk/mag/artnov99/rotih.html">rotifers</a>, one class of which has reproduced without sex for millions of years.</p>
<p>Theory says they should be extinct, but clearly they aren’t. So how have they done it? </p>
<p>DNA sequencing now shows that they make up for their lack of sex by incorporating genes from other rotifers of the same or different species, or even from fungi and bacteria.</p>
<p>You’ll find rotifers in ponds or puddles. Under the microscope they’re incredibly cute little (smaller than 1mm) multicelled invertebrates, motoring around like tiny paddle-steamers.</p>
<p>This is an illusion from the circle of whirling cilia around their heads that drives them forward and wafts tasty algae and decaying scum through their tough little jaws.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/UDxu_XEGfEI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<p>When their puddle dries up, rotifers shrink into dehydrated specks that look like crinkly barrels. They can stay that way for years and blow around to new pools. They rehydrate in just a few hours, and can efficiently patch up their DNA, broken in many places during desiccation.</p>
<p>This insignificant little creature poses a big problem for understanding one of biology’s oldest mysteries: why do animals have sex?</p>
<h2>Why sex?</h2>
<p>Sex is spectacularly inefficient. Animals waste a lot of time and energy courting and keeping a mate. Worse, half the population have no offspring. </p>
<p>The “why sex?” question was first asked by Charles Darwin 150 years ago. Ever since, evolutionary geneticists have wondered <a href="http://www.pbs.org/wgbh/evolution/sex/">why sex</a> seems always to win the evolutionary race over asexual reproduction. </p>
<p>Many theories have been put forward and debated over decades. The most accepted is that sex is useful for shuffling new gene combinations by recombining parent genomes. </p>
<p>This enables animals to adapt to changed environments and colonise new ecological niches. Importantly, all these new combinations of genes help animals to keep pathogens at bay by giving them a “moving target”. </p>
<h2>Sex in animals</h2>
<p>In mammals, sexual reproduction is obligatory – we can’t do <a href="http://theconversation.com/is-virgin-birth-possible-yes-unless-you-are-a-mammal-52379">virgin birth</a>. A few reptile and frog species reproduce by <a href="http://www.britannica.com/science/parthenogenesis">parthenogenesis</a>, in which the female makes diploid eggs from combinations of her own genes. But offspring developed from unfertilised eggs are less fit than their sexual sisters. So asexual species don’t last long.</p>
<p>Many invertebrates can reproduce both sexually and asexually, and some (such as aphids) indulge in sex only sporadically, in response to environmental cues. But there are none that never have sex – except for bdelloid rotifers. </p>
<p>In the hundreds of years since the Dutch scientist <a href="http://www.britannica.com/biography/Antonie-van-Leeuwenhoek">Antonie van Leeuwenhoek</a> first saw bdelloid rotifers under his newly invented microscope, no-one has ever spotted a male.</p>
<p>Females lay eggs but there is no meiosis (the reduction division that produces sperm or eggs), so her eggs all contain genomes identical to hers.</p>
<p>Genomes of bdelloid rotifers are weird. There are two copies of each gene as you expect of a diploid, but they are very different. This suggests that they originated as a hybrid between two species whose <a href="http://science.sciencemag.org/content/288/5469/1211">genes and genomes diverged 60 million years ago</a>. </p>
<p>Their homologous chromosomes have been differently rearranged so they can’t pair at meiosis. The conclusion is that bdelloid rotifers have eschewed sex for 60 million years. </p>
<h2>New DNA for rotifers</h2>
<p>Sequencing a bdelloid rotifer genome produced a big surprise, as about 8% of the genes <a href="http://www.nature.com/nature/journal/v500/n7463/full/nature12326.html">looked foreign</a>. Some genes were typical of fungi or bacteria, and endowed the rotifer with handy new properties such as breaking down toxins or <a href="http://dx.doi.org/10.1371/journal.pgen.1003035">using new foodstuffs</a>. This “<a href="http://www.britannica.com/science/horizontal-gene-transfer">horizontal transfer</a>” between rotifers and other organisms is <a href="http://bmcbiol.biomedcentral.com/articles/10.1186/s12915-015-0202-9">ancient and ongoing</a>.</p>
<p>Foreign DNA is spread all over the rotifer genome. So how did it get there? It seems that dehydration makes holes in cell membranes that <a href="http://www.ncbi.nlm.nih.gov/pubmed/20421328">can suck up DNA</a>. The rotifers’ efficient mechanism for repairing double stranded DNA breaks in dehydrated animals is perfect for incorporating foreign DNA into the genome.</p>
<p>More extraordinary still is what happens to DNA from other rotifer individuals or species. It isn’t incorporated just anywhere in the genome, but lines up with the <a href="http://dx.doi.org/10.1016/j.cub.2016.01.031">appropriate DNA sequence and recombines</a>. This means that a new version of a particular gene may replace the old. Just like sex.</p>
<h2>Bacteria can do it</h2>
<p>This ability to take up and use DNA from the environment isn’t unique to rotifers. </p>
<p>Bacteria reproduce by fission to make clones of genetically identical cells. But they can <a href="http://www.ncbi.nlm.nih.gov/pubmed/7968924">take up DNA from another bacterial strain</a>, swap it for the resident gene, and express a variant protein in the wild. This “DNA transformation” provided the first evidence that genes are made from DNA.</p>
<p>DNA transformation is only one of several tricks that bacteria use to scavenge variant and novel genes. Bacteria can also receive little packages of foreign bacterial genes by way of a virus.</p>
<p>Some bacteria can exchange long DNA molecules – even the whole genome – through tube-like structures. This conjugation looks most like what we would consider sex. </p>
<p>In throwing up a great variety of genotypes, sexual reproduction still seems to be the best bet in the long run – for vertebrates and invertebrates.</p>
<p>In its absence, organisms such as the tiny rotifers have had to find other ways to boost their gene pool.</p>
<p>Far from falsifying the theory that genetic variation is essential for evolutionary success, rotifers brilliantly confirm it.</p><img src="https://counter.theconversation.com/content/56913/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jenny Graves has received funding from the Australian research Council and the National Health and Medical research Council. </span></em></p>Rotifers are tiny creatures found in ponds or puddles and can reproduce without sex. The theory says they should not have survived so how have they done it?Jenny Graves, Distinguished Professor of Genetics, La Trobe UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/554072016-02-29T16:38:21Z2016-02-29T16:38:21ZWhy did sex evolve? Researchers edge closer to solving longstanding mystery<figure><img src="https://images.theconversation.com/files/113036/original/image-20160226-26719-16v67gr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.google.com/search?hl=en&q=bonobo+apes&tbm=isch&tbs=simg:CAQSjAEaiQELEKjU2AQaAggADAsQsIynCBpiCmAIAxIozgvrC4MFvRXPC_1MK7AvNC_1AKhB6cOps6ri22OLU4qy2lLcIksjikLRowZ1Try-Zqf04XVTjNizAXiRrJvCI-mucnkqNIU9bUQHFqEyGNFZ4tFHL7Yo4F_1OCGIAMMCxCOrv4IGgoKCAgBEgSAHiZBDA&sa=X&ved=0ahUKEwiEk9bx-pzLAhWHuRoKHUKmAjwQwg4IGigA&biw=1143&bih=570&dpr=1.2#q=bonobo+apes&hl=en&tbs=simg:CAQSjAEaiQELEKjU2AQaAggADAsQsIynCBpiCmAIAxIozgvrC4MFvRXPC_1MK7AvNC_1AKhB6cOps6ri22OLU4qy2lLcIksjikLRowZ1Try-Zqf04XVTjNizAXiRrJvCI-mucnkqNIU9bUQHFqEyGNFZ4tFHL7Yo4F_1OCGIAMMCxCOrv4IGgoKCAgBEgSAHiZBDA,sur:fmc&tbm=isch&imgrc=VPi3aPfhadF8oM%3A">Chris Ryan/youtube</a></span></figcaption></figure><p>The reason why, in terms of evolution, organisms have sex may seem rather obvious – they do it to reproduce. Clearly, natural selection must favour individuals who can reproduce over those who can’t. But this is missing the point. For many species there is an alternative: asexual reproduction. </p>
<p>So why has sex evolved in so many species? Surprisingly, there’s no single clear answer to this question. Indeed, to date, researchers have developed more than <a href="http://www.ncbi.nlm.nih.gov/pubmed/8409359">20 different hypotheses</a>. Lately, a number of experiments have started testing these theories, taking us closer to finding a solution.</p>
<p>In asexual species, a female reproduces without the genetic contribution of a male and makes daughters effectively identical to herself. Anyone who’s had their roses blighted by plant lice (<a href="http://tidcf.nrcan.gc.ca/en/insects/factsheet/5371">alias: greenflies or aphids</a>) will know just how successful a strategy this can be. </p>
<p>Key to the intellectual problem is the fact that males often do no investing into the offspring. While sexual mothers need to produce both sons and daughters, an asexual female can make daughters alone. If females are the investing sex (they make eggs, feed the young etc), this makes it far easier to quickly grow the population: one asexual female can become two, two can become four, four can become eight etc. This has been confirmed by <a href="http://rspb.royalsocietypublishing.org/content/262/1363/45">experiments</a> comparing effectively asexual beetles with sexual beetles in the lab.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/113035/original/image-20160226-26687-vqrotf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/113035/original/image-20160226-26687-vqrotf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113035/original/image-20160226-26687-vqrotf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113035/original/image-20160226-26687-vqrotf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113035/original/image-20160226-26687-vqrotf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113035/original/image-20160226-26687-vqrotf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113035/original/image-20160226-26687-vqrotf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Aphids.</span>
<span class="attribution"><span class="source">wikimedia</span></span>
</figcaption>
</figure>
<p>Apart from mammals (including humans) and birds, there are asexual species in just about every taxonomic group, including some fish, reptiles, plants and insects – but they are uncommon. So despite the advantages of asexual reproduction, this tells us that in the longer term, sex wins. </p>
<h2>Bad mutations versus adaptation</h2>
<p>Evolutionary research into the problem has largely centred on two broad classes of hypotheses. They are both based on the fact that sex generates variation by mixing up the genetic makeup of the parents. You and I are not identical copies of our parents, whereas the daughters of an asexual aphid are.</p>
<p>This variation is manifested at the genetic level: sex generates some organisms within the species with lots of harmful mutations and some with relatively few. Supporters of the so-called <a href="http://www.ncbi.nlm.nih.gov/pubmed/22691203">mutational deterministic theory</a> argue that if organisms with many mutations have disproportionately low survival chances, many bad mutations tend to die out with their hosts, generating a large number of organisms that are free from such mutations. In asexual species, because of this lack of variation, no individual is especially burdened by mutations. As a consequence, no one mutational death removes that many harmful mutations.</p>
<p>This theory is increasingly being questioned, however, as it is becoming clear that many sexual species, including <a href="http://www.ncbi.nlm.nih.gov/pubmed/17203060/">insects</a> and <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3878865/">plants</a>, are not actually producing as many harmful mutations as the theory requires.</p>
<p>Another strong contender hypothesis states that sex enables a lineage to <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3341334/">adapt to changing conditions</a>. Experiments do confirm that members of a sexual lineage usually adapt faster than asexual members of the same species when conditions change. Indeed the <a href="http://rspb.royalsocietypublishing.org/content/262/1363/45">beetle experiment</a> mentioned above has shown that if a sexual population is allowed freely to evolve during changing conditions, it may displace the asexual population altogether. </p>
<p>There may be many reasons why sex facilitates adaptation. For example, imagine two individuals in an asexual population that both have a good but different mutation. Because their DNA can’t mix, their descendents end up competing with each other (this is called clonal interference) – you will never get the benefits of both mutations in one individual. In a sexual population, however, both of the good mutations can find their way into one individual. This way, we get the benefit of both, which makes adaptation a lot easier. A molecular-level study <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature17143.html">published on 24 February</a> has confirmed that sex does indeed alleviate clonal interference.</p>
<h2>The Queen theory: parasites?</h2>
<p>So increasing the speed of adaptation seems to be a pretty good explanation. But what happens after an environmental change has taken place and the conditions have stabilised? Should we not expect the asexuals to again out-compete the sexuals? For this reason, many researchers are increasingly attracted to the idea that the variation created by sex also enables species to adapt in the never-ending evolutionary arms race with their parasites.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/113034/original/image-20160226-26673-11zpkvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/113034/original/image-20160226-26673-11zpkvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=888&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113034/original/image-20160226-26673-11zpkvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=888&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113034/original/image-20160226-26673-11zpkvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=888&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113034/original/image-20160226-26673-11zpkvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1116&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113034/original/image-20160226-26673-11zpkvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1116&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113034/original/image-20160226-26673-11zpkvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1116&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Go get them, parasites!</span>
<span class="attribution"><span class="source">cea +/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>This sort of evolutionary game of cat and mouse is known as <a href="http://www.indiana.edu/%7Ecurtweb/Research/Red_Queen%20hyp.html">Red Queen evolution</a>, from the character in Alice in Wonderland who insisted that one must run just to stay in the same place. Indeed, genes related to immunity are some of the fastest evolving we have. There is also <a href="http://science.sciencemag.org/content/349/6249/747">recent evidence</a> that species can increase the amount of genetic mixing they do when they sense that they are infected with a parasite. This means their offspring will be even more different from one another and their parents. </p>
<p>We also know the disadvantages of a lack of variation in asexual crop plants. For example, attack by parasites led to the <a href="http://www.britannica.com/event/Great-Famine-Irish-history">Irish potato famine</a> in 1845–49. Currently bananas are <a href="http://www.fao.org/in-action/banana-varieties-resistant-to-fungus-are-identified-using-mutation-induction/en/">under threat</a> from attack by numerous fungal parasites. This is concerning given that over 95% of the export trade in bananas is of just one asexual strain (Cavendish). </p>
<p>So do organisms have sex to make sure their descendents won’t be wiped out by disease – or to make them relatively free of harmful mutations? These hypotheses don’t have to be mutually exclusive. Researchers in the field are increasingly interested in some sort of hybrid model. </p>
<p>Currently, we are moving towards studies of the <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature17143.html">evolution of sex at the molecular level</a> – so we can map the exact mutations that are lost or gained during adaptation. Studies of the fate of mutations as a result of the co-evolution of hosts and parasites are also just around the corner. A major issue remains, however: understanding why more species don’t have the best of both worlds (as indeed aphids do), and have both sexual and asexual reproductive phases.</p><img src="https://counter.theconversation.com/content/55407/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Laurence D. Hurst receives funding from BBSRC, MRC, ERC and The Evolution Education Trust. </span></em></p>There’s long been a lack of evidence for why sex has become so much more common than asexual reproduction across nearly all species. Thankfully, this is now slowly changing.Laurence D. Hurst, Professor of Evolutionary Genetics at The Milner Centre for Evolution, University of BathLicensed as Creative Commons – attribution, no derivatives.