tag:theconversation.com,2011:/id/topics/geckos-11434/articles
geckos – The Conversation
2018-12-06T17:14:21Z
tag:theconversation.com,2011:article/108266
2018-12-06T17:14:21Z
2018-12-06T17:14:21Z
Geckos walk on water – we filmed them to find out how
<figure><img src="https://images.theconversation.com/files/249339/original/file-20181206-128190-1iy9hvu.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/image-photo/colorful-macro-closeup-green-day-gecko-564753997?src=lCXUCR48828mRWAZXzvu_A-1-85">Natalia Van D/Shutterstock</a></span></figcaption></figure><p>Anyone who’s seen a gecko will likely know they can climb walls. But these common lizards can also run across water nearly as fast as they can move on solid ground. Yet while we know how geckos scale smooth vertical surfaces using countless tiny hairs on their feet called setae, how they manage to avoid sinking into the water has been something of a mystery – until now. My colleagues and I <a href="http://www.cell.com/current-biology/fulltext/S0960-9822(18)31469-6">recently completed research</a> that explains how geckos use a combination of techniques to perform this amazing feat.</p>
<p>The ability to walk on water has been recorded in smaller animals such as the <a href="https://www.nature.com/articles/nature01793">water strider</a>, which are light enough to be held up by the water’s surface tension, the force between the water molecules at the surface. Meanwhile, larger animals such as <a href="http://jeb.biologists.org/content/218/8/1235">the grebe</a>, can walk on water because they are powerful enough to slap the surface with their feet as they run. The fast movement pushes down the water beneath the foot, creating a pocket of air around it. The upwards force generated when this pocket is pushed under the water is what keeps the animal briefly suspended on the surface.</p>
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<p>But geckos are typically a size that falls in between these two categories. They are too weak to hold themselves up using surface slapping alone and too heavy to leave the water’s surface unbroken. Yet their relative water running speeds approach those of another well-known water running lizard, <a href="https://www.nature.com/articles/380340a0">the basilisk</a> (or “Jesus lizard”), which does rely on the slapping technique.</p>
<p>Initial calculations hinted, and video analysis confirmed, that unlike other species that move at the water’s surface, geckos use a combination of techniques to move faster on top of the water than they can by swimming through it. By analysing videos of geckos moving across the water, we found that their gait was similar to that of the basilisk. Each step involves retracting the foot through the air, slapping the surface, and stroking beneath the water. </p>
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<img alt="" src="https://images.theconversation.com/files/249258/original/file-20181206-128199-nsyi2n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/249258/original/file-20181206-128199-nsyi2n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=216&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249258/original/file-20181206-128199-nsyi2n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=216&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249258/original/file-20181206-128199-nsyi2n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=216&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249258/original/file-20181206-128199-nsyi2n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=271&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249258/original/file-20181206-128199-nsyi2n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=271&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249258/original/file-20181206-128199-nsyi2n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=271&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">No bridge? No problem.</span>
<span class="attribution"><span class="source">Pauline Jennings</span></span>
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<p>But <a href="https://www.ncbi.nlm.nih.gov/pubmed/9320547">unlike basilisks</a>, which aren’t affected by changes in the water’s surface tension, our experiments showed that geckos’ speed and head height were cut by half when we added detergent to the water, reducing the surface tension. This suggests that they are at least partly using the forces between the water molecules to stay above the surface. </p>
<p>We also found that geckos crucially use a combination of hydrostatic force (the upwards push of the water known as buoyancy) and hydrodynamic force (the lift created by movement across the water’s surface like in a surface-skimming motorboat). Together, these forces generate additional lift for the gecko, a condition known as <a href="https://www.globalsecurity.org/military/systems/ship/semi-planing.htm">semi-planing</a>.</p>
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<img alt="" src="https://images.theconversation.com/files/249260/original/file-20181206-128211-1i3yhj4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/249260/original/file-20181206-128211-1i3yhj4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=604&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249260/original/file-20181206-128211-1i3yhj4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=604&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249260/original/file-20181206-128211-1i3yhj4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=604&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249260/original/file-20181206-128211-1i3yhj4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=759&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249260/original/file-20181206-128211-1i3yhj4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=759&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249260/original/file-20181206-128211-1i3yhj4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=759&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">The gecko combo.</span>
<span class="attribution"><span class="source">Current Biology</span></span>
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<h2>Sting in the tail</h2>
<p>For all the ingenuity of this multi-tasking approach, geckos can only keep their head and torso fully above the water, leaving their tails dragging underneath. Being able to move almost as fast as on land when almost half of your body is underwater and facing more resistance and drag forces is quite a feat – just ask Michael Phelps.</p>
<p>Geckos manage this by using their tail, which has already been shown to help them <a href="https://www.nature.com/articles/s41598-017-11484-7">manoeuvre around obstacles</a>, <a href="http://www.pnas.org/content/105/11/4215">jump</a> and <a href="http://jeb.biologists.org/content/212/5/604">escape predators</a>. Seen from above as it travels across the water, the gecko can resemble a crocodile, moving its body and tail with a wavelike motion to create propulsion to balance the backwards pull of the water.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/wbKVZIhloaM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<p>Our research shows that for medium-sized animals to move quickly along the surface of water a complex and clever combination of physical mechanisms is required that previously was thought only to occur in larger and smaller animals. But it could also feed into better designs for animal-inspired robots. </p>
<p>Previous studies on geckos have inspired several such “biomimetic” endeavours, from <a href="https://geckskin.umass.edu/">better adhesives</a> to an agile (and pretty adorable) tailed robot car, aptly named <a href="https://blogs.scientificamerican.com/observations/robot-uses-lizard-tail-to-leap/">Tailbot</a>. Better understanding of how animals travel across complex terrains will hopefully lead to robots that can harness these techniques to move on both land and water with the high performance seen in geckos.</p><img src="https://counter.theconversation.com/content/108266/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jasmine Nirody 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>
Understanding geckos’ movements could lead to better robots.
Jasmine Nirody, Post-Doctoral Research Fellow in Biophysics, University of Oxford
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/100064
2018-08-13T11:52:17Z
2018-08-13T11:52:17Z
Five ways that natural nanotechnology could inspire human design
<figure><img src="https://images.theconversation.com/files/231100/original/file-20180808-142251-ey5sqw.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/image-photo/blue-morpho-butterfly-iridescent-tropical-native-484889716">Michael Fitzsimmons/Shutterstock</a></span></figcaption></figure><p>Though nanotechnology is portrayed as a <a href="https://theconversation.com/five-ways-nanotechnology-is-securing-your-future-55254">fairly recent human invention</a>, nature is actually full of nanoscopic architectures. They underpin the essential functions of a variety of life forms, from bacteria to berries, wasps to whales. </p>
<p>In fact, tactful use of the principles of nanoscience can be traced to natural structures that are over 500m-years-old. Below are just five sources of inspiration that scientists could use to create the next generation of human technology.</p>
<h2>1. Structural colours</h2>
<p>The colouration of several types of <a href="https://www.chemistryworld.com/feature/structural-colour/3009020.article">beetles and butterflies</a> is produced by sets of carefully spaced nanoscopic pillars. Made of sugars such as chitosan, or proteins like keratin, the widths of slits between the pillars are engineered to manipulate light to achieve certain colours or effects like iridescence.</p>
<p>One benefit of this strategy is resilience. Pigments tend to bleach with exposure to light, but structural colours are stable for remarkably long periods. <a href="https://doi.org/10.1073/pnas.1210105109">A recent study</a> of structural colouration in metallic-blue marble berries, for example, featured specimens collected in 1974, which had maintained their colour despite being long dead. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/228220/original/file-20180718-142414-6o4gw8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/228220/original/file-20180718-142414-6o4gw8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/228220/original/file-20180718-142414-6o4gw8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=640&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228220/original/file-20180718-142414-6o4gw8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=640&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228220/original/file-20180718-142414-6o4gw8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=640&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228220/original/file-20180718-142414-6o4gw8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=804&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228220/original/file-20180718-142414-6o4gw8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=804&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228220/original/file-20180718-142414-6o4gw8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=804&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Complex slit architecture in the wings of the butterfly Thecla opisena.</span>
<span class="attribution"><a class="source" href="http://advances.sciencemag.org/content/3/4/e1603119">Science Advances/Wilts et al</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Another advantage is that colour can be changed by simply varying the size and shape of the slits, and by filling the pores with liquids or vapours too. In fact, often the first clue to the presence of structural colouration is a vivid colour change after the specimen has been soaked in water. Some wing structures are so sensitive to air density in the slits that colour changes are seen in <a href="https://www.nature.com/articles/s41598-017-01273-7">response to temperature</a> too. </p>
<h2>2. Long range visibility</h2>
<p>In addition to simply deflecting light at an angle to achieve the appearance of colour, some ultra-thin layers of slit panels completely reverse the direction of the travel of light rays. This deflection and blocking of light can work together to create stunning optical effects such as a <a href="https://www.livescience.com/92-advanced-optics-butterfly-wings.html">single butterfly’s wings</a> with <a href="http://rsif.royalsocietypublishing.org/content/1/1/49">half-a-mile visibility</a>, and beetles with <a href="http://science.sciencemag.org/content/315/5810/348">brilliant white scales</a>, measuring a slim five micrometers. In fact, these structures are so impressive that they can outperform artificially engineered structures that are 25 times thicker.</p>
<h2>3. Adhesion</h2>
<p>Gecko feet can bind firmly to practically any solid surface in milliseconds, and detach with no apparent effort. This adhesion is <a href="https://doi.org/10.1073/pnas.192252799">purely physical</a> with <a href="https://webdisk.lclark.edu/xythoswfs/webui/_xy-1594799_1-t_d9VVAITO">no chemical interaction</a> between the feet and surface. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/228215/original/file-20180718-142438-hrk1sp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/228215/original/file-20180718-142438-hrk1sp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/228215/original/file-20180718-142438-hrk1sp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=228&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228215/original/file-20180718-142438-hrk1sp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=228&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228215/original/file-20180718-142438-hrk1sp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=228&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228215/original/file-20180718-142438-hrk1sp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=287&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228215/original/file-20180718-142438-hrk1sp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=287&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228215/original/file-20180718-142438-hrk1sp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=287&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Micro and nanostructure of Gecko feet.</span>
<span class="attribution"><a class="source" href="http://www.pnas.org/content/102/2/385">© 2005, The National Academy of Sciences</a></span>
</figcaption>
</figure>
<p>The active adhesive layer of the gecko’s foot is a branched nanoscopic layer of bristles called “spatulae”, which measure about 200 nanometers in length. Several thousand of these spatulae are attached to micron sized “seta”. Both are made of very flexible keratin. Though research into the finer details of the spatulae’s attachment and detachment mechanism is ongoing, the very fact that they operate with no sticky chemical is an impressive feat of design. </p>
<p>Gecko’s feet have other fascinating features too. They are <a href="https://doi.org/10.1073/pnas.0408304102">self-cleaning</a>, resistant to self-matting (the seta don’t stick to each other) and are detached by default (including from each other). These features have <a href="http://rsta.royalsocietypublishing.org/content/366/1870/1575">prompted suggestions</a> that in the future, glues, screws and rivets could all be made from a single process, casting keratin or similar material into different moulds. </p>
<h2>4. Porous strength</h2>
<p>The strongest form of any solid is the single crystal state – think diamonds – in which atoms are present in near perfect order from one end of the object to the other. Things like steel rods, aircraft bodies and car panels are not single crystalline, but polycrystalline, similar in structure to a mosaic of grains. So, in theory, the strength of these materials could be improved by increasing the grain size, or by making the whole structure single crystalline. </p>
<p>Single crystals can be very heavy, but nature has a solution for this in the form of nanostructured pores. The resultant structure – a meso-crystal – is the strongest form of a given solid for its weight category. Sea urchin spines and <a href="https://www.livescience.com/1694-secret-abalone-shell-strength-revealed.html">nacre</a> (mother of pearl) are both made of meso-crystalline forms. These creatures have lightweight shells and yet can reside at great depths where the pressure is high.</p>
<p>In theory, meso-crystalline materials can be manufactured, although using existing processes would require a lot of intricate manipulation. Tiny nanoparticles would have to be spun around until they line up with atomic precision to other parts of the growing mesocrystals, and then they would need to be gelled together around a soft spacer to eventually form a porous network.</p>
<h2>5. Bacterial navigation</h2>
<p><a href="https://www.nature.com/scitable/knowledge/library/bacteria-that-synthesize-nano-sized-compasses-to-15669190">Magnetotactic bacteria</a> posses the extraordinary ability to sense minute magnetic fields, including the Earth’s own, using small chains of nanocrystals called magnetosomes. These are grains sized between 30–50 nanometers, made of either magnetite (a form of iron oxide) or, less commonly, greghite (an iron sulphur combo). Several features of magnetosomes work together to produce a foldable “compass needle”, many times more sensitive than man-made counterparts. </p>
<p>Though these “sensors” are only used for navigating short distances (magnetotactic bacteria are pond-dwelling), their precision is incredible. Not only can they find their way, but varying grain size means that they can retain information, while growth is restricted to the most magnetically sensitive atomic arrangements. </p>
<p>However, as oxygen and sulphur combine voraciously with iron to produce magnetite, greghite or over 50 other compounds – only a few of which are magnetic – great skill is required to selectively produce the correct form, and create the magnetosome chains. Such dexterity is currently beyond our reach but future navigation could be revolutionised if scientists learn how to mimic these structures.</p><img src="https://counter.theconversation.com/content/100064/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Thomas Prabhakar 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>
There are countless nanoscopic architectures in nature, creating iridescence, sticky feet, magnetic navigation – and more.
John Thomas Prabhakar, Lecturer of Physical Chemistry (Nanocrystals and Nanoparticles), Bangor University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/81770
2017-08-01T04:46:43Z
2017-08-01T04:46:43Z
Big-headed gecko shows human actions are messing with evolution
<figure><img src="https://images.theconversation.com/files/180381/original/file-20170731-728-1k82dcf.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://pixabay.com/en/leopard-gecko-eye-pet-yellow-2125784/">PIxabay</a></span></figcaption></figure><p>Evolution doesn’t have to take millions of years. <a href="http://www.pnas.org/cgi/doi/10.1073/pnas.1709080114">New research</a> shows that a type of lizard living on man-made islands in Brazil has developed a larger head than its mainland cousins in a period of only 15 years.</p>
<p>The group of insect-eating geckos from the species <a href="http://reptile-database.reptarium.cz/species?genus=Gymnodactylus&species=amarali"><em>Gymnodactylus amarali</em></a> was isolated from the rest of the population when areas of the countryside were flooded to provide hydro-electric power. This caused the extinction of some larger species of lizards on the new islands, leaving the geckos to eat insects that would normally have been mopped up by the bigger species. As a result, the geckos have evolved bigger mouths, and so bigger heads, that enable them to eat their larger prey more easily.</p>
<p>We’ve actually seen rapid evolution like this before, but usually in response to a natural disaster such as <a href="http://www.d.umn.edu/%7Ejetterso/Ecological%20Genetics/documents/GrantandGrant1995Predictingmicroevolutionarychange.pdf">drought</a> or <a href="http://science.sciencemag.org/content/early/2009/07/02/science.1173668">climate change</a>. What’s different about the geckos is that they’ve evolved in direct response to an environmental change enacted by humans, demonstrating just how much impact we can have on the natural world.</p>
<p>The gecko study, <a href="http://www.pnas.org/cgi/doi/10.1073/pnas.1709080114">published in PNAS</a>, gives us an interesting demonstration of how evolution works, not just because the change has happened within our lifetimes. Those geckos among the original colony that had larger heads (and mouths) could eat a wider range of prey and so had more energy to put into survival and reproduction. As a result, they had more children and their genes for larger heads spread to a greater proportion of the next generation. This continued until larger heads had become a common feature of the group.</p>
<p>But why just those with bigger heads? Why didn’t geckos whose whole bodies were bigger receive the same evolutionary advantage? Well larger bodies take more energy to maintain, so those individuals would lose the advantage that they gain by eating more food.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/180382/original/file-20170731-20214-1e7g0ci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/180382/original/file-20170731-20214-1e7g0ci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=295&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180382/original/file-20170731-20214-1e7g0ci.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=295&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180382/original/file-20170731-20214-1e7g0ci.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=295&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180382/original/file-20170731-20214-1e7g0ci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=370&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180382/original/file-20170731-20214-1e7g0ci.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=370&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180382/original/file-20170731-20214-1e7g0ci.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=370&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gymnodactylus amarali.</span>
<span class="attribution"><span class="source">Carlos Eduardo Ribeiro Cândido, Universidade de Brasília</span></span>
</figcaption>
</figure>
<p>One of the most interesting things about this research is that the geckos on all five of the islands studied have evolved larger heads, even though they were isolated from each other. This suggests that increasing head size without increasing body size is the most efficient way to take advantage of the opportunity to eat a more varied diet than is normal for this species. </p>
<p>This kind of rapid evolution has been seen before, including among the finches of the Galapagos Islands that <a href="https://theconversation.com/darwins-finches-highlight-the-unity-of-all-life-38039">helped Charles Darwin</a> formulate his theory of natural selection in the first place. One of these finches species reduced the average size of its bill in a period of <a href="http://science.sciencemag.org/content/313/5784/224?variant=full-text&sso=1&sso_redirect_count=1&oauth-code=7d865c1f-58de-4b42-a83e-5f7034cb8d0c">just 22 years</a> when a competitor with a larger bill colonised the island.</p>
<p>The larger species ate all the larger seeds with tough shells, a large bill that still couldn’t compete became a disadvantage for the finches and so those birds with a smaller beak began to thrive. This is one of the fundamental principles of biology: if you don’t need a particular structure you <a href="https://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/bjps/44/3/10.1093_bjps_44.3.409/1/409.pdf?Expires=1501349306&Signature=QOun8ATlF8gJ9dQ5JlVnmmCAVXnIxuzb60t1u1moIR3rPIsXvthemcNQrc5LirJt1NdKoBbJwQFwtoZ-64ZF7gqUq%7Ekv0A9V1ACLMsksqtmPIdt75J3p2FoVDAbCirHOYc3rtRlPUSfEPQ14cmv2cV%7E3vO1Bc0YPIcyOQUVSqrOhscPxtshU4WlstpMyhmA31k749vEK5me0b1E8ZMdKhu5%7EiwyHR6fxmfjo%7EG%7Eg0aDfe6V234T4BjnpSel-znkujfG3MJhTiWFAPeHuhVUlP9WUkGzQvtm4k64EU4lJcUns-ia482EQIC1hzGayvhKD22f57m2MjQClAMg%7EO6cvfw__&Key-Pair-Id=APKAIUCZBIA4LVPAVW3Q">don’t bother to grow it</a> and save the energy instead.</p>
<p>A similar instance <a href="http://science.sciencemag.org/content/sci/346/6208/463.full.pdf?ijkey=VheIecEk3oS0E&keytype=ref&siteid=sci">occurred in Florida</a> when a lizard called the Cuban brown anole, which is much larger than the native green anole, colonised areas of Florida. The green anole promptly retreated up into the treetops and within 20 generations had evolved bigger, stickier foot pads, a helpful characteristic for the high life.</p>
<h2>Human impact</h2>
<p>Another example of rapid evolutionary change was <a href="http://science.sciencemag.org/content/early/2009/07/02/science.1173668">found in Soay sheep</a> on the island of Hirta in St Kilda off the coast of Scotland. After the residents of the island were evacuated in 1930, the sheep were allowed to run wild and, within 25 years, began to get smaller. The explanation put forward for this is that milder winters caused by climate change are allowing smaller lambs to survive, bringing down the average size of the whole population.</p>
<p>This suggests that we should expect to see many more examples of rapid evolution as the climate continues to change in response to greenhouse gas emissions. But the new study on geckos shows that localised human action can also interfere with the processes of evolution. Although the change in head and mouth size in the gecko seems benign, we should remember it came about because of the extinction of four other species of lizard in the area linked to the flooding. It’s a timely reminder that climate change is not the only issue facing biodiversity and evolutionary processes.</p><img src="https://counter.theconversation.com/content/81770/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jan Hoole 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 group of lizards in Brazil have evolved bigger heads in just 15 years thanks to their new environment.
Jan Hoole, Lecturer in Biology, Keele University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/69505
2016-11-29T11:15:59Z
2016-11-29T11:15:59Z
Glues inspired by nature will give us faster ships, surgical adhesives and sticky car tyres
<figure><img src="https://images.theconversation.com/files/147903/original/image-20161129-10969-tnaadr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Barncales stick with glue like no other.</span> <span class="attribution"><a class="source" href="http://www.geograph.org.uk/photo/4073228">Neil Theasby</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>We use adhesives all the time, from the temporary stickiness of the humble Post-It note to super-strength glues used in construction, but it is easy to overlook the many living creatures that rely on adhesion for survival in the natural world. </p>
<p>Adhesion can be used to permanently attach to a surface, as climbing plants and <a href="https://museumvictoria.com.au/discoverycentre/infosheets/how-do-barnacles-cement-themselves-to-rocks/">barnacles</a> do. It can help creatures get around, for example on the feet of <a href="http://www.livescience.com/47307-how-geckos-stick-and-unstick-feet.html">geckos</a> and various insects. Some creatures such as salamanders or <a href="http://video.nationalgeographic.com/video/weirdest-sea-cucumber">sea cucumbers</a> use glue as a defence against predators, while others such as <a href="https://asknature.org/strategy/web-glue-is-strong-adhesive/">spiders</a> and <a href="http://www.livescience.com/39047-new-velvet-worm-species.html">velvet worms</a> use it as a means of attack. Some even use adhesion during reproduction. But despite their frequent appearance in nature, most natural glues are poorly understood.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/147917/original/image-20161129-10957-19tmgm5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/147917/original/image-20161129-10957-19tmgm5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=373&fit=crop&dpr=1 600w, https://images.theconversation.com/files/147917/original/image-20161129-10957-19tmgm5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=373&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/147917/original/image-20161129-10957-19tmgm5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=373&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/147917/original/image-20161129-10957-19tmgm5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=469&fit=crop&dpr=1 754w, https://images.theconversation.com/files/147917/original/image-20161129-10957-19tmgm5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=469&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/147917/original/image-20161129-10957-19tmgm5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=469&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gecko: sticky feet.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/24931020@N02/13468259683/in/photolist-mw9mnR-nUdA8C-41oqA-6rDYoU-5pt3qK-e9kGmF-5aevMj-4w11VL-4w11YL-nS1m9L-4w122N-6rzSiK-7uCuqr-qrCoDw-bziXqo-537DjS-9xa6xC-cj4QDs-9beSdq-9xa2fG-dJLuFP-4AKE7-4AKGd-bvLg9s-dZcCzd-9x9ZUu-98KM-dofg4F-bJF3Lz-bvLfZq-oU8Wky-4AKBN-HQMKaM-HQML4a-GUXok3-4AKJg-HMKnY1-4zqJr3-8P94yK-bvLfRN-V89rn-oBF6rY-fgBcdJ-7Q9tx-aeubi5-8iozcv-9Xja2-HQMLtD-b8jV4e-nwB3EU">Ozzy Delaney/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Nature, it seems, rarely does anything in the most straightforward of ways and adhesives are no different. Scientists must therefore be creative when trying to understand these amazing natural materials. For example, it’s not the fact that the Golden Gate Bridge is made out of steel and concrete that allows it to stand over San Francisco Bay – it is the engineering techniques that work with the properties of steel and concrete to carefully balance physical forces. In a similar way, simply knowing the chemical composition of natural adhesives is not enough. </p>
<p>The <a href="http://www.americanscientist.org/issues/feature/2006/2/how-gecko-toes-stick">toe pads of geckos</a> and <a href="https://asknature.org/strategy/byssus-threads-resist-forces/">byssus threads</a> of marine mussels (their “beards”), for example, are formidably complex feats of engineering, of which the chemical composition is only one element. </p>
<p>When it comes to mussels, each byssus thread is injection moulded in place along the full length of the mussel’s foot, which temporarily connects the body of the mussel to the surface. Two types of collagen produce an elastic gradient between the hard rock and soft mussel tissue, which distributes the physical stresses of wave action or attack from predators. More than half a dozen specialised proteins and enzymes generate the thread’s sticky properties and form the permanent attachment to the surface. On top of that, the mussel can also choose where and when to attach. </p>
<p>To understand the adhesion process properly we need to understand the physics, the chemistry and the biology. It is what we call a multidisciplinary problem – in other words, it’s complicated. The challenge for bio-inspired technologies in general, and adhesives specifically, is to identify the important elements of the system and simplify them so that they can be translated, artificially recreated, and turned into products that we can all benefit from.</p>
<h2>More uses for nature’s products</h2>
<p>Why are biological glues so interesting to us? Because there are numerous technical applications where progress has been hampered by a lack of appropriate adhesives, and where natural adhesives have already solved the problems. Bioadhesives can do things that most synthetic glues cannot – joining surfaces underwater, for example. Human surgery is a clear application for such a glue. </p>
<p>One of the most common procedures during pregnancy is <a href="http://www.nhs.uk/conditions/amniocentesis/Pages/Introduction.aspx">amniocentesis</a>, used to test a foetus for Down syndrome. This carries a risk because it perforates the foetal membrane which cannot subsequently heal. Bio-inspired adhesives and sealants that can heal these perforations could help to significantly reduce instances of <a href="https://www.acs.org/content/acs/en/pressroom/newsreleases/2014/august/solving-a-sticky-problem-with-fetal-surgery-using-a-glue-inspired-by-the-sandcastle-worm.html">pre-term delivery</a>. Based on natural molecules like proteins and carbohydrates, bio-inspired glues could also reduce the need for unpleasant chemicals such as formaldehyde to manufacture adhesives, reducing the environmental impact of the industry.</p>
<p>In other instances, knowledge of adhesion could help us to design non-stick surfaces – anti-fouling coatings for the hulls of ships that prevent creatures like barnacles from attaching, causing drag, slowing ships, using more fuel and increasing the emission of greenhouse gases. Or other materials that prevent bacterial biofilms, or slimes, from accumulating in food processing plants, on medical implants, environmental sensors or in your washing machine.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/bFiOkxoXLic?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Wouldn’t it be nice to have streets free from chewing gum, clothes that resist the onslaught of messy children and windows that shed dust and dirt? All of these have potential solutions in nature. You don’t need to take my word for it: take a cabbage leaf (Savoy is best) and look how droplets of water roll off, collecting dirt as they go. This is the so-called <a href="https://asknature.org/strategy/surface-allows-self-cleaning/">lotus effect</a> which works through a combination of the surface chemistry and texture of the leaves. A natural, self-cleaning material.</p>
<p>Adhesion is everywhere and the benefits of understanding it are clear. But it can be a challenge to link up the necessary expertise to tackle the biology, chemistry and physics of such complex systems in a coordinated way. This has led to the establishment of a four year-long, EU-funded <a href="http://www.cost.eu/COST_Actions/ca/CA15216">European Network of Bioadhesion Expertise</a>, which will help bring together researchers from across Europe to address the biological aspects of adhesion in nature, from frogs to fungi, as well as the fundamental physical and chemical processes that underpin it.</p>
<p>What will come of research into natural glues? It might be car tyres based on the toe pads of tree frogs that grip the road better in wet conditions, climbing robots based on geckos, or specialist adhesives for hi-tech applications. It was recently suggested by researchers that <a href="http://www.redorbit.com/news/science/1113412094/sorry-marvel-fans-spider-man-is-physically-impossible-and-heres-why-011915/">Spiderman’s powers of attachment are impossible</a>. I, for one, remain hopeful.</p><img src="https://counter.theconversation.com/content/69505/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nick Aldred's research is supported by Office of Naval Research awards N00014-13-1-0633/4, COST Action 15216 and a Newcastle University SAgE Faculty Fellowship.</span></em></p>
Nature has created some of the strongest glues with properties we could use – if we understood how they worked.
Nick Aldred, SAgE Research Fellow, Newcastle University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/56510
2016-03-24T00:56:43Z
2016-03-24T00:56:43Z
Hidden housemates: a gecko invasion?
<figure><img src="https://images.theconversation.com/files/116700/original/image-20160330-13683-uxh6sb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A native Australian gecko, Gehyra dubia.</span> <span class="attribution"><span class="source">Eric Vanderduys</span></span></figcaption></figure><p>In northern Australia some houses are filled nightly with chatter. You might hear a distinctive “chuck-chuck-chuck”, or find calling cards (droppings) on skirting boards, picture frames and window sills. If so, you probably have gecko housemates. </p>
<p>If you live anywhere from Brisbane to Broome, it is likely your house is home to two very similar species, the introduced Asian House Gecko (<em>Hemidactylus frenatus</em>) and one of several species of native Australian counterparts, the dtellas (<em>Gehyra sp.</em>).</p>
<p>Other native species you might see around your house include the velvet geckos (<em>Oedura sp</em>), while other introduced species include the Mourning Gecko (<em>Lepidodactylus lugubris</em>).</p>
<p>As nocturnal reptiles, geckos generally hide during the day and emerge at night. The species we see around our homes are taking advantage of the insect-attracting lights that fill our cities and towns. These provide an endless smorgasbord of food for the geckos.</p>
<p>Asian House Geckos established themselves in Darwin in the 1960s. It is most likely they travelled here as stowaways in cargo ships. Since then their distribution has expanded along transport routes. They are now found along the northern and eastern coasts, most commonly around buildings or other manmade structures. </p>
<h2>Who are your gecko housemates?</h2>
<p>Check a reptile field guide to see which geckos are in your area. Most of them can be identified fairly easily, but if you live with Asian House Geckos (<em>Hemidactylus frenatus</em>) and dtellas (species of <em>Gehyra</em>) you will need to pay extra attention. </p>
<p>The following tips will help you tell your <em>Hemidactylus</em> from your <em>Gehyra</em>:</p>
<ul>
<li>Looks: Both species are similar in size, about 11 cm total body length, and are pinkish-brown to dark grey with velvety skin and large eyes. If you look closely, the Asian House Geckos have spines on either side of their tail. Each of their toes has claws. Dtellas, on the other hand, are spineless. They have claws on their outer toes but the toe closest to their body is clawless.</li>
</ul>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/116122/original/image-20160323-32312-3b8r9e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/116122/original/image-20160323-32312-3b8r9e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/116122/original/image-20160323-32312-3b8r9e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/116122/original/image-20160323-32312-3b8r9e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/116122/original/image-20160323-32312-3b8r9e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/116122/original/image-20160323-32312-3b8r9e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/116122/original/image-20160323-32312-3b8r9e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/116122/original/image-20160323-32312-3b8r9e.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"></a>
<figcaption>
<span class="caption">The Asian House Gecko arrived in Australia in the ‘60s. If you look closely, you can see spines running down its tail.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/magdalena_b/5567730558/in/photolist-fNjuGE-g5L496-9u15js-g5K5Gv-5x5zbR-6GnQCQ-9u14oh">magdalena_b/Flickr</a></span>
</figcaption>
</figure>
<ul>
<li><p>Call: Asian House Geckos are much louder and more talkative than natives; their “chuk-chuk-chuk” is sometimes described as “scolding”, whereas native geckos tend to chatter very softly.</p></li>
<li><p>Eggs: Both Asian House Geckos and native geckos lay one or two eggs that are round, hard-shelled and resistant to moisture loss. </p></li>
</ul>
<h2>Who rules the house?</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/116124/original/image-20160323-32323-1xhojm3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/116124/original/image-20160323-32323-1xhojm3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/116124/original/image-20160323-32323-1xhojm3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=906&fit=crop&dpr=1 600w, https://images.theconversation.com/files/116124/original/image-20160323-32323-1xhojm3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=906&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/116124/original/image-20160323-32323-1xhojm3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=906&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/116124/original/image-20160323-32323-1xhojm3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1139&fit=crop&dpr=1 754w, https://images.theconversation.com/files/116124/original/image-20160323-32323-1xhojm3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1139&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/116124/original/image-20160323-32323-1xhojm3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1139&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An intrepid gecko’s eggs laid in a keyhole.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/yeled/86799048/in/photolist-8EScz-8ESkj-fp5qyQ-8ES6E-CayXqJ-bYv29w-6hc4SM">Charlie Allom/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Are introduced geckos pushing out our native species? While they have been <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1442-9993.2010.02143.x/full">implicated in the exclusion of native house geckos</a>, the extent of this is unknown. </p>
<p>One theory is that the hunting style of the Asian House Gecko gives them an advantage under bright city lights. These geckos are active hunters and can feed efficiently where insects congregate around artificial light. Native geckos, on the other hand, seem to forage where prey is more dispersed. </p>
<p>Indeed, <a href="http://onlinelibrary.wiley.com/doi/10.1111/aec.12287/full">Asian House Geckos are willing to use more brightly lit areas</a>, whereas natives choose darker areas. </p>
<p>While Asian House Geckos may have access to more insects in light areas, it’s possible that some native species and the house gecko are exploiting different parts of the “house gecko niche” and happily living together.</p>
<h2>Geckos in the bush</h2>
<p>Asian House Geckos have been recorded in natural habitats away from our homes. Could they invade native bushland?</p>
<p>On various islands of the Pacific and Indian oceans, introduced Asian House Geckos displace resident geckos from the house-gecko niche and have managed to spread beyond areas of human habitation. Most notably, in the Mascarene Islands, <a href="http://www.sciencedirect.com/science/article/pii/S0006320705001850">Asian House Geckos have invaded all natural habitats</a>. This has led to the decline of the native <em>Nactus</em> gecko populations and the extinction of three species.</p>
<p>But <a href="http://www.publish.csiro.au/?paper=ZO12077">perhaps this is not the case in Australia</a>. Surveys conducted across northern Australia failed to find evidence that Asian House Geckos were successfully invading natural habitats. Based on this study, it seems this species will continue to thrive with people but is unlikely to spread further. More research is underway to investigate if Asian House Geckos are invading the bush in different parts of their range.</p>
<p>Scientists agree, however, that novel parasites and pathogens carried by Asian House Geckos could pose a threat to Australian wildlife. We don’t know, but it’s definitely something to watch.</p>
<p>Next time you come across your gecko housemates, take a closer look. Are you harbouring native species, or a potential invader?</p>
<p><em>Correction: the lead image on this article was corrected on March 30 2016. The original image was incorrectly described as a native gecko.</em></p><img src="https://counter.theconversation.com/content/56510/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lin Schwarzkopf receives funding from the Australian Research Council, and Meat and Livestock Australia. </span></em></p><p class="fine-print"><em><span>Heather Neilly 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>
If you’re hearing a strange chatter in your home, you may have gecko housemates.
Heather Neilly, PhD Candidate, Centre for Tropical Biodiversity and Climate Change Navigation, James Cook University
Lin Schwarzkopf, Professor in Zoology, James Cook University
Licensed as Creative Commons – attribution, no derivatives.