tag:theconversation.com,2011:/us/topics/rattlesnakes-50128/articlesrattlesnakes – The Conversation2020-06-07T11:20:21Ztag:theconversation.com,2011:article/1370712020-06-07T11:20:21Z2020-06-07T11:20:21ZRattlesnakes on a plain: How cars, pollution and suburbia threaten these mysterious creatures<figure><img src="https://images.theconversation.com/files/339857/original/file-20200604-67372-1lalp9k.jpg?ixlib=rb-1.1.0&rect=262%2C305%2C4369%2C3529&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An adult male western rattlesnake soaking up some sun after emerging from hibernation.</span> <span class="attribution"><span class="source">(Marcus Atkins)</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Just like the hordes of mountain bikers, hikers and trail runners that migrate from their comfortable couches to more open spaces in spring, western rattlesnakes are also on the move, emerging from deep winter dens to their summer foraging grounds. </p>
<p>For years, <a href="https://karllarsen.sites.tru.ca/publications/">our research group</a> at Thompson Rivers University has been investigating population trends and movements of the world’s most northerly populations of rattlesnakes, found in the Okanagan Valley of British Columbia. The western rattlesnake (<em>Crotalus oreganus</em>) is one of three species of rattlesnake found in Canada, and the only one in B.C., although they also live as far south as Baja California.</p>
<p>Snakes are particularly interesting in Canada because their active season — warm temperatures that allow them to go about their lives — is far shorter than it is for their relatives to the south. The harsh Canadian winters limit the places where a rattlesnake can hole up and wait out the snow. This historically lead to dozens of snakes of all different species using communal dens, but this phenomenon is becoming increasingly rare. </p>
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<img alt="" src="https://images.theconversation.com/files/339858/original/file-20200604-67399-6607lg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/339858/original/file-20200604-67399-6607lg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/339858/original/file-20200604-67399-6607lg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/339858/original/file-20200604-67399-6607lg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/339858/original/file-20200604-67399-6607lg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/339858/original/file-20200604-67399-6607lg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/339858/original/file-20200604-67399-6607lg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Western rattlesnakes emerging from a winter den.</span>
<span class="attribution"><span class="source">(Marcus Atkins)</span>, <span class="license">Author provided</span></span>
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<p>Rattlesnakes are threatened in B.C., and many populations are declining at alarming rates. Although the idea of being rid of snakes may be inviting to some, it will surely have cascading consequences for already threatened grassland ecosystems. For example, rattlesnakes are key players in grassland food chains, acting as mid-level predators that control rodent populations and serve as a food source for larger predators like the endangered North American badger. </p>
<h2>What can you learn from following rattlesnakes?</h2>
<p>Rattlesnakes often <a href="https://doi.org/10.1670/13-138">make substantial migrations from their winter dens to their summer habitat</a>, sometimes several kilometres. The dens are often in secluded areas, yet snakes can encounter a number of dangers on their path. </p>
<p>Perhaps the biggest threat to snakes in Canada is roads, where even low traffic back-roads can have catastrophic impacts on otherwise healthy snake populations. Road mortality is a leading cause of the decline for snakes in B.C. One study found the population was being reduced by <a href="https://doi.org/10.3354/esr01017">6.6 per cent per year, which would lead to a 97 per cent decrease in the population in just 40 years</a>.</p>
<p>Snakes are also threatened by pollution, human persecution and steady habitat degradation and fragmentation. When their habitat overlaps with human landscapes, such as vineyards, orchards, golf courses, campgrounds or hiking trails, they tend to be of <a href="https://doi.org/10.1111/acv.12208">poorer body condition</a> than snakes that inhabit relatively natural environments. </p>
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<img alt="" src="https://images.theconversation.com/files/339859/original/file-20200604-67368-bjgol0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/339859/original/file-20200604-67368-bjgol0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/339859/original/file-20200604-67368-bjgol0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/339859/original/file-20200604-67368-bjgol0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/339859/original/file-20200604-67368-bjgol0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/339859/original/file-20200604-67368-bjgol0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/339859/original/file-20200604-67368-bjgol0.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">A rattlesnake eating a squirrel.</span>
<span class="attribution"><span class="source">(Marcus Atkins)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Historically a large number of the rattlesnakes in B.C. were found in the Okanagan Valley, a region that is <a href="https://www.investkelowna.com/application/files/7715/3815/6564/2018_Central_Okanagan_Economic_Profile_-_RSPDF.pdf">experiencing one of the fastest rates of urban and agricultural growth in Canada</a>. Unfortunately, this means snake habitat isn’t about to improve. Still, the animals persist in select pockets of quality habitat.</p>
<h2>Beware the ‘danger noodle’</h2>
<p>Despite their iconic buzzing rattle, the warning display for which these animals are named, rattlesnakes are notoriously difficult to find. This is because the rattle that tips off unsuspecting hikers to the presence of a “<a href="https://www.mnn.com/earth-matters/animals/blogs/boaty-mcboatface-inspires-internet-rename-animals">danger noodle</a>” is really the last-ditch effort to scare off intruders before the animals resort to biting. </p>
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<a href="https://images.theconversation.com/files/339860/original/file-20200604-67351-1fcbjhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/339860/original/file-20200604-67351-1fcbjhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/339860/original/file-20200604-67351-1fcbjhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=810&fit=crop&dpr=1 600w, https://images.theconversation.com/files/339860/original/file-20200604-67351-1fcbjhp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=810&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/339860/original/file-20200604-67351-1fcbjhp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=810&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/339860/original/file-20200604-67351-1fcbjhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1018&fit=crop&dpr=1 754w, https://images.theconversation.com/files/339860/original/file-20200604-67351-1fcbjhp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1018&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/339860/original/file-20200604-67351-1fcbjhp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1018&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Watch your step! Can you spot the rattler?</span>
<span class="attribution"><span class="source">(Marcus Atkins)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Rattlesnakes rely heavily on their mottled camouflage to hide among rocks and bushes to avoid detection completely — and they are quite good at it. Their skill at hide-and-seek means it is incredibly difficult for scientists to estimate their population numbers — how can you count something you can’t see? </p>
<p>Because rattlesnakes are so difficult to count, there has only been <a href="http://bcparks.ca/eco_reserve/campbellb_er/ecology_of_northern_pacific_rattlesnake.pdf?v=1587081600179">one comprehensive study of a rattlesnake population in B.C., which dates back to 1985</a>, when graduate J. Malcolm Macartney studied a population on a private cattle ranch.</p>
<p>In an effort to determine how rattlesnake populations have changed over the past 35 years, we have been scrambling up cliff faces in search of the same rattlesnake dens that Macartney surveyed decades ago.</p>
<p>These steep cliff faces, dotted with towering ponderosa pines, give way to lush grassland meadows fringed by azure lake waters. Although the location has not changed, the landscape certainly has. In 1986, just one year after Macartney wrapped up his rattlesnake population study, half of the area was fenced off and established as a provincial park dedicated to recreation. </p>
<p>This creates a unique natural experiment where half of the rattlesnake population has remained on an active cattle ranch closed to the public, and the other half within one of the busiest parks in the area seeing nearly 250,000 visitors per summer. </p>
<h2>Keeping snakes for years to come</h2>
<p>Although we may still be several months away from fully understanding the trends of this rattlesnake population, we have learned much about how these animals interact with the land, and those who share it with them.</p>
<p>Are rattlesnakes that dwell on landscapes largely devoid of humans more likely to be larger and more abundant than snakes in areas with high levels of human visitation? We are currently analyzing our data to answer this very question. </p>
<p>Rattlesnakes living in areas where humans seldom visit also appear more likely to rattle at passersby. Snakes that regularly encounter people are 10 times less likely to rattle than those living in areas undisturbed by humans. </p>
<p>Although this work is very preliminary, it suggests that rattlesnakes are altering their behaviour according to the presence of humans in their foraging grounds. Perhaps they are learning that they don’t necessarily need to waste precious energy with exuberant warnings. </p>
<p>Understanding exactly why these animals are declining and shifting their behaviour is a much more complicated issue, but it brings to attention the delicate balance between conservation and recreation. If we hope to keep rattlesnakes around, we will have to adjust how we interact with the limited amount of habitat available to them. </p>
<p>So, if you plan to spend some time in B.C.’s beautiful grasslands, remember to stay snake awake!</p><img src="https://counter.theconversation.com/content/137071/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Karl Larsen receives funding from NSERC (federal), the Habitat Conservation Trust Fund (BC) and the Forest Enhancement Society (BC)</span></em></p><p class="fine-print"><em><span>Marcus Atkins receives funding from the Habitat Conservation Trust Foundation, the Forest Enhancement Society of BC, and BC Parks.</span></em></p>At current rates, the rattlesnake population in British Columbia could be severely depleted by 2060.Karl Larsen, Professor, Department of Natural Resource Sciences, Thompson Rivers UniversityMarcus Atkins, MSc. Student, Environmental Science, Thompson Rivers UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1140402019-03-22T13:54:47Z2019-03-22T13:54:47ZHere’s what that house proud mouse was doing – plus five other animals who take cleaning seriously<figure><img src="https://images.theconversation.com/files/265294/original/file-20190322-36283-1me4pb6.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3772%2C3342&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/house-mouse-standing-on-rear-feet-137911070">Szasz-Fabian Jozsef/Shutterstock</a></span></figcaption></figure><p>A house proud mouse, considerately tidying up the workbench of the shed in which it lives, has been captured on video and shared online. The mouse pops out of a box, picks up some screws, nail clippers and a metal chain and carries them back into the box. It’s tempting to think the mouse is cleaning up its home in the same way that a human would. Of course, in biology, things are rarely that simple. </p>
<p>Cleaning a living area for hygienic reasons isn’t unusual in animals. <a href="https://www.newscientist.com/article/mg23731604-900-smell-of-death-tells-undertaker-bees-its-time-to-remove-corpses/">Bees will remove corpses from the hive</a>, <a href="http://sciencenetlinks.com/science-news/science-updates/fatherly-fish/">male fish will pick bits of mould and silt</a> from their eggs. <a href="https://insider.si.edu/2017/09/clean-sexy-panamas-golden-collared-manakins/">Clearing debris from a display area is common in birds</a> that dance to attract a mate. None of these apply to the mouse, so we need to look for an explanation that is based in the innate behaviours of rodents.</p>
<p><a href="https://www.terminix.com/pest-control/rats/pack-rat/">Packrats</a> in North America have a habit of collecting shiny objects, stones and wood to protect their nests. Some mice like to keep a good larder – when food is plentiful, <a href="https://scholar.google.co.uk/scholar?as_ylo=2015&q=hoarding+in+rodents&hl=en&as_sdt=1,5">they will hoard it</a>. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1108021056650936320"}"></div></p>
<p>Many rodents <a href="https://www.sciencedirect.com/science/article/pii/S0166432897001629">bury novel objects</a> that they find in their territory and this is sometimes thought to be an <a href="https://link.springer.com/article/10.1007/s00213-009-1466-y">extension of the natural digging response</a> that all rodents have. Mice and rats are keen tunnellers so the urge to dig is an important part of their behavioural repertoire. </p>
<p>Mice also <a href="https://journals.sagepub.com/doi/pdf/10.1258/002367796780684890">manipulate their bedding</a> to make a nest. Though it’s difficult to be sure with only a short video as evidence, it’s possible that the mouse’s behaviour is rooted in these responses of hoarding, burying and generally manipulating its environment. All those objects in the mouse’s territory may have triggered confusion, leading the mouse to stash them somewhere it perceives as safe.</p>
<p>So animals are lot tidier than you think and not just this one mouse. Cleanliness is a virtue for a whole host of critters.</p>
<h2>1. Rattlesnakes</h2>
<p><a href="https://bioone.org/journals/the-southwestern-naturalist/volume-60/issue-4/0038-4909-60.4.374/Habitat-Manipulation-in-Hunting-Rattlesnakes-iCrotalusi-Species/10.1894/0038-4909-60.4.374.short">Rattlesnakes</a> lack limbs but still tidy their hunting grounds using their triangular heads and muscular necks to move aside grass. </p>
<p>Decluttering their space may give them a clearer path to potential prey – extremely beneficial for a predator that cannot correct its aim after launching an attack.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/265286/original/file-20190322-36279-10d9cld.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/265286/original/file-20190322-36279-10d9cld.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/265286/original/file-20190322-36279-10d9cld.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/265286/original/file-20190322-36279-10d9cld.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/265286/original/file-20190322-36279-10d9cld.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/265286/original/file-20190322-36279-10d9cld.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/265286/original/file-20190322-36279-10d9cld.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">A rattlesnake flattens and shifts grass aside to get a clear shot at prey.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/farmboyted/14617656300/in/photolist-ogHiWU-9jw6rM-dCfWfn-6y1ck2-c2CDiY-RGff8s-bG6tL6-c2CEbJ-9jzc1o-9w5Yfp-6sxh9w-ogHrdC-cgaB7m-bEwkSw-9JbsYF-foqXDe-6Cmu9U-bwJnLm-fLb2J6-nqk2Cj-ym6-9jw5Zi-ym8-4r8K3z-eANoh-9JehDw-UguVim-3nXx8s-4K1mgu-fogVFW-q6C2jS-ym7-6xSBRx-2d2p5Wr-9jw5Ev-BcT-QbmR2k-9Bnf6F-9jDYMa-9jDYrK-8cCaYz-mGPGL-bVzTZz-4qEDUu-o2NHhu-7K7Luz-e9yo9a-9jDYHe-FLJo4-cU9sFW">Flickr/Farmboyted</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>2. Songbirds</h2>
<p>Songbirds are known to haul their chicks’ “faecal sacs” and drop them outside the nest. <a href="https://www.jstor.org/stable/1370361?seq=1#page_scan_tab_contents">Bluebirds</a> have been seen draping faecal sacs on electric wires, fence posts and utility poles. The birds are quite strict at removing faeces, uneaten food and dead nestlings immediately, to prevent infection and to make the nest harder for predators to detect.</p>
<h2>3. Ants</h2>
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<a href="https://images.theconversation.com/files/265292/original/file-20190322-36244-y7lxvm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/265292/original/file-20190322-36244-y7lxvm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/265292/original/file-20190322-36244-y7lxvm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=795&fit=crop&dpr=1 600w, https://images.theconversation.com/files/265292/original/file-20190322-36244-y7lxvm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=795&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/265292/original/file-20190322-36244-y7lxvm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=795&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/265292/original/file-20190322-36244-y7lxvm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=999&fit=crop&dpr=1 754w, https://images.theconversation.com/files/265292/original/file-20190322-36244-y7lxvm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=999&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/265292/original/file-20190322-36244-y7lxvm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=999&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A plaster cast of an ant colony, with visible tunnels and chambers.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Ant_colony#/media/File:Ant_Nest.jpg">Shaners Becker/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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</figure>
<p>The risk of disease is especially serious for social animals. Social insects such as ants and bees live in large numbers within very confined spaces, making them vulnerable to contagions. It is for this reason that many <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0118376">ant species</a> carry their dead out of the nest rather than leaving the corpses to fester in the tunnels. </p>
<p><a href="https://royalsocietypublishing.org/doi/10.1098/rsbl.2014.0306">One study</a> found that if ants were prevented from removing the dead bodies, they were more likely to die. However, Indian jumping ants have a slightly different method – their nests include a “rubbish” chamber which is filled with dead ants, left over prey and faecal matter. These chambers are staffed by a “sewage crew” of maggots that eat the refuse and prevent the chamber getting clogged.</p>
<h2>4. Naked mole rats</h2>
<p>Naked mole rats also live underground and follow a similar system to the ants. They build special toilet areas in their burrows, and when these are full, “waste worker” mole rats plug it with soil and dig a new one. Mole rats are quite meticulous when it comes to their tunnels – whisking away any unruly roots, pebbles and other litter in the passageways. </p>
<p><a href="https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.1971.tb04544.x">In one study</a>, scientists planted cables and a thermometer in a mole rat burrow, which were promptly cleared away by the “cleaning crew”.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/jin0dGcFjao?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<h2>5. Damselfish</h2>
<p>For those of you who watched the BBC’s Blue Planet II, you may remember the footage of the garibaldi damselfish tirelessly removing sea urchins from their nest areas, only to find the next day that it was again covered in sea urchins. </p>
<p>Much of the work of rearing offspring is handled by the male. Upon becoming an adult, a male garibaldi will <a href="https://www.nps.gov/chis/learn/nature/garibaldi.htm">select a promising stretch of reef</a> where he will live for the rest of his life. In addition to removing sea urchins from their nest areas, the garibaldi will remove debris, sea stars that wander along, and gnaw away all the plant growth except for a few species of red algae. These he trims so they are about an inch long, which is perfect for the eggs to rest in.</p>
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<p>Just like physical traits, behavioural traits aren’t just influenced by the environment, they can also be inherited. Certain traits make some individuals more likely to reproduce and pass on their genes than others – such as an insistence on cleanliness to prevent disease or predation. As much as we like to think that humans are special and unique, it’s worth recalling the words of Charles Darwin, who said: “The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind.”</p><img src="https://counter.theconversation.com/content/114040/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>The mouse who tidied the shed he lives in fascinated human viewers, but cleanliness isn’t a virtue unique to humans.Sophia Daoudi, Lecturer in Psychology, University of StirlingJan Hoole, Lecturer in Biology, Keele UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1136192019-03-21T13:29:55Z2019-03-21T13:29:55ZSnake venom can vary in a single species — and it’s not just about adaptation to their prey<p>Few sights and sounds are as emblematic of the North American southwest as a defensive rattlesnake, <a href="https://www.youtube.com/watch?v=XkyKliH1X3c">reared up, buzzing, and ready to strike</a>. The message is loud and clear, “Back off! If you don’t hurt me, I won’t hurt you.” Any intruders who fail to heed the warning can expect to fall victim to a venomous bite. </p>
<p>But the consequences of that bite are surprisingly unpredictable. Snake venoms are complex cocktails made up of dozens of individual toxins that attack different parts of the target’s body. The composition of these cocktails is highly variable, even within single species. Biologists have come to assume that most of this variation reflects adaptation to what prey the snakes eat in the wild. But <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2018.2735">our study</a> of the Mohave rattlesnake (<em>Crotalus scutulatus</em>, also known as the Mojave rattlesnake) has uncovered an intriguing exception to this rule.</p>
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<a href="https://images.theconversation.com/files/264483/original/file-20190318-28512-19ykw6y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264483/original/file-20190318-28512-19ykw6y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/264483/original/file-20190318-28512-19ykw6y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264483/original/file-20190318-28512-19ykw6y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264483/original/file-20190318-28512-19ykw6y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264483/original/file-20190318-28512-19ykw6y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264483/original/file-20190318-28512-19ykw6y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264483/original/file-20190318-28512-19ykw6y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">What’s in those glands? It depends where you are!</span>
<span class="attribution"><span class="source">W. Wüster</span></span>
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<p>A 20-minute drive can take you from a population of this rattlesnake species with a highly lethal neurotoxic venom, <a href="https://www.ncbi.nlm.nih.gov/pubmed/11990148">causing paralysis and shock</a>, to one with a haemotoxic venom, causing <a href="https://www.sciencedirect.com/science/article/pii/0041010183900545">swelling, bruising, blistering and bleeding</a>. The neurotoxic venom (known as venom A) can be more than ten times as lethal as the haemotoxic venom (venom B), at least to lab mice. </p>
<p>The Mohave rattlesnake is not alone in having different venoms like this – several other rattlesnake species display the <a href="https://www.sciencedirect.com/science/article/pii/0041010185900145">same variation</a>. But why do we see these differences? Snake venom evolved to subdue and kill prey. One venom may be better at killing one prey species, while another may be more toxic to different prey. Natural selection should favour different venoms in snakes eating different prey – it’s a classic example of evolution through natural selection.</p>
<p>This idea that snake venom varies due to adaptation to eating different prey has become <a href="https://www.sciencedirect.com/science/article/pii/S0169534712002935">widely accepted</a> among herpetologists and toxinologists. Some have found <a href="https://www.nature.com/articles/379537a0">correlations</a> between venom and prey. Others have shown <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2009.0048">prey-specific lethality</a> of venoms, or identified toxins <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2018.1003">fine-tuned for killing the snakes’ natural prey</a>. The venom of some snakes even <a href="https://www.jstor.org/stable/3893080">changes along with their diet as they grow</a>. </p>
<p>We expected the Mohave rattlesnake to be a prime example of this phenomenon. The extreme differences in venom composition, toxicity and mode of action (whether it is neurotoxic or haemotoxic) seem an obvious target for natural selection for different prey. And yet, when we correlated differences in venom composition with regional diet, we were shocked to find there is no link.</p>
<h2>Variable venoms</h2>
<p>In the absence of adaptation to local diet, we expected to see <a href="https://www.ncbi.nlm.nih.gov/pubmed/30395254">a connection between</a> gene flow (transfer of genetic material between populations) and venom composition. Populations with ample gene flow would be expected to have more similar venoms than populations that are genetically less connected. But once again, we drew a blank – there is no link between gene flow and venom. This finding, together with the geographic segregation of the two populations with different venoms, suggests that instead there is strong local selection for venom type. </p>
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<span class="caption">Mohave rattlesnake feeding on a kangaroo rat, one of its most common prey items.</span>
<span class="attribution"><span class="source">W. Wüster</span></span>
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<p>The next step in our research was to test for links between venom and the physical environment. Finally, we found some associations. The haemotoxic venom is found in rattlesnakes which live in an area which experiences warmer temperatures and more consistently low rainfall compared to where the rattlesnakes with the neurotoxic venom are found. But even this finding is deeply puzzling. </p>
<p>It has been suggested that, as well as killing prey, venom <a href="https://www.sciencedirect.com/science/article/pii/0041010179902113">may also help digestion</a>. Rattlesnakes eat large prey in one piece, and then have to digest it in a race against decay. A venom that starts predigesting the prey from the inside could help, especially in cooler climates where digestion is more difficult. </p>
<p>But the rattlesnakes with haemotoxic venom B, which better aids digestion, are found in warmer places, while snakes from cooler upland deserts invariably produce the non-digestive, neurotoxic venom A. Yet again, none of the conventional explanations make sense.</p>
<p>Clearly, the selective forces behind the extreme venom variation in the Mohave rattlesnake are complex and subtle. A link to diet may yet be found, perhaps through different kinds of <a href="https://academic.oup.com/icb/article/56/5/1032/2420622">venom resistance</a> in key prey species, or prey dynamics affected by local climate. In any case, our results reopen the discussion on the drivers of venom composition, and caution against the simplistic assumption that all venom variation is driven by the species composition of regional diets.</p>
<p>From a human perspective, variation in venom composition is the bane of anyone working on snakebite treatments, or antidote development. It can lead to unexpected symptoms, and <a href="https://www.ncbi.nlm.nih.gov/pubmed/28847519">antivenoms may not work</a> against some populations of a species they supposedly cover. Anyone living within the range of the Mohave rattlesnake can rest easy though – the available antivenoms cover both main venom types. </p>
<p>Globally, however, our study underlines the unpredictability of venom variation, and shows again that there are no shortcuts to understanding it. Those developing antivenoms need to <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3767246/">identify regional venom variants and carry out extensive testing</a> to ensure that their products are effective against all intended venoms.</p><img src="https://counter.theconversation.com/content/113619/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Wolfgang Wüster receives funding from The Leverhulme Trust. </span></em></p><p class="fine-print"><em><span>Giulia Zancolli receives funding from Santander Early Career Research Scholarship. </span></em></p>The Mohave rattlesnake is famous for its variable venom – but the reasons behind that variation are not as straightforward as we thought.Wolfgang Wüster, Senior Lecturer in Zoology, Bangor UniversityGiulia Zancolli, Associate Research Scientist, Université de LausanneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/912762018-03-14T07:10:24Z2018-03-14T07:10:24ZNew insights into how southern African pythons look after their babies<figure><img src="https://images.theconversation.com/files/206927/original/file-20180219-75971-sstbow.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hatchling southern African pythons bask outside the nest chamber.</span> <span class="attribution"><span class="source">Graham Alexander</span></span></figcaption></figure><p>Snakes are probably not the first creatures that spring to mind when you think about caring parents. But recent research has shown that several snake species are far more tender than their reputation suggests. We know now, for instance, that rattlesnakes <a href="http://scholar.google.co.za/scholar_url?url=https%3A%2F%2Fwww.researchgate.net%2Fprofile%2FGordon_Schuett%2Fpublication%2F280445130_Social_Behavior_of_Rattlesnakes_A_Shifting_Paradigm%2Flinks%2F55b50ae808ae9289a08a6673%2FSocial-Behavior-of-Rattlesnakes-A-Shifting-Paradigm&hl=en&sa=T&oi=gga&ct=gga&cd=4&ei=yB-MWoDsI4XKmgGllL44&scisig=AAGBfm27nuKIsVryexRNHhXhOPYWgfZtsA&nossl=1&ws=1920x940">den communally in winter</a> while some species can recognise their kin.</p>
<p>I spent seven years studying wild pythons in the <a href="http://www.dinokengreserve.co.za/">Dinokeng Game Reserve</a> north of Pretoria, South Africa. Pythons were implanted with radio-transmitters and temperature recording dataloggers. When females laid eggs, I used surveillance video cameras installed in the underground nest chambers, usually in aardvark burrows, to record the behaviour of the breeding mothers and their babies in a natural setting.</p>
<p>I have made some important findings. For example, while it is well known that python mothers across all species incubate their eggs, we’ve now learned that southern African python mothers go one step further. They remain at the nest site with their newly-hatched young for two weeks or more. This discovery, which I recently <a href="http://onlinelibrary.wiley.com/doi/10.1111/jzo.12554/full">published in the Journal of Zoology</a>, marks the first known case of mothers in egg-laying snake species remaining with the clutch after the babies had hatched.</p>
<p>And I discovered that when southern African female pythons breed they change colour to almost black during the six month cycle. This process, known as facultative melanism, has not been reported in snakes before. It’s probably an adaptation that allows for faster rates of heating during basking, which is important for keeping the eggs and hatchlings warm.</p>
<p>This study highlights just how much there still is to discover about snakes. Even large, iconic snakes such as pythons still harbour many secrets. Unravelling the secrets matters because knowing more about the reproductive biology of snakes and lizards can reveal shed light on the evolution of parental care in birds and mammals.</p>
<h2>Making babies and changing colour</h2>
<p>Mating in southern African pythons is a serious business, and is rarely just a one-night stand. Some males were recorded remaining with receptive females for months. In one instance a male followed a female for more than 2 kilometres over a three month period. And when he went through a shedding cycle and got left behind, he found her again after she had moved a kilometre away.</p>
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<p>The female’s dark breeding coloration, and the resulting heat retention, is important. Mothers of some types of python, such as Burmese python, are able to metabolically raise their body temperature, using the heat to incubate their eggs. This physiological response is termed <a href="http://www.bioone.org/doi/abs/10.1670/12-050">facultative thermogenesis</a>. </p>
<p>The southern African python and Burmese python are close relatives, but southern African pythons are not able to generate heat in this way. They rely solely on basking to raise their body temperature to almost 40 °C, then return to the nest cavity and coil around their eggs to warm them with their sun-derived body heat.</p>
<p>Body temperatures of receptive, pregnant and brooding female southern African pythons are more than 5 °C warmer than non-reproductive females. Even the body temperatures of baby-attending mothers are significantly higher than non-breeding females. These high temperatures are thought to improve egg development in the female, help with incubation and then help the babies to digest the last remaining egg yolk once they have hatched. </p>
<p>After southern African python babies hatch, they remain at the nest site with the mother. For the first day or so, they remain on the clutch of eggs, but they then regularly trek to the surface where they bask for short periods tightly packed together with their nest mates. At night, the babies rest protected and warmed in their mother’s coils in the nest chamber. The babies shed their skin 12 to 14 days after hatching. A few days later, they all disperse from the nest during the night.</p>
<h2>A gruelling process</h2>
<p>Reproduction takes a lot out of a female southern African python. Breeding females lose about 40% of their pre-laying body mass. In spite of this, they devote themselves to their clutch and don’t feed during their pregnancy, egg brooding and while they stay with their young – a period of more than six months.</p>
<p>By the time they leave the nest, the females start foraging for food, typically by lying in ambush along a game path. The most common prey for large female pythons are impala and grey duiker, but a wide range of prey can be on the menu.</p>
<p>They may take several years to recover their body condition. So, at best, wild female southern African pythons breed only every other year. Males, meanwhile, are sexually active every year.</p><img src="https://counter.theconversation.com/content/91276/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Graham Alexander receives funding from the National Research Foundation. </span></em></p>Mating in southern African pythons is a serious business, and is rarely just a one-night standGraham Alexander, Professor of Herpetology, Environmental Physiology and Physiology, Ecology and Evolution, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.