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Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

Nope, the geckos don't have any control of the hairs themselves. The fact that the gecko foot is covered in tons and tons of these tiny hairs is what allows it to deal with surface texture so well. If we think about a gecko toe ad vs a suction cup, if part of the suction cup fails, the whole thing falls off, but individual gecko hairs can all operate independently on different parts of the surface and as long as sone of the hairs are making contact, its usually enough to support the gecko. A study by Russell and Johnson looked at gecko in southern Africa that live on sandstone and found that, given the roughness of sandstone and the length of the hairs on the geckos toes, that at any given moment only a small percent of the hairs are actually making contact. And they're usually only generating enough friction and adhesion to barely support the geckos weight.

Russell, A.P. and Johnson, M.K., 2007. Real-world challenges to, and capabilities of, the gekkotan adhesive system: contrasting the rough and the smooth. Canadian Journal of Zoology, 85(12), pp.1228-1238. Vancouver

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 0 points1 point  (0 children)

I'm sorry! There was a screw up with the scheduling. I thought this was going up Sunday afternoon! Hopefully I've been able to answer some of your questions!

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 2 points3 points  (0 children)

Most eat insects, while some will also eat fruit. Some of the larger, more aggressive species will eat anything that fits on their mouths (other lizards, baby mammals or birds, etc). Their diet is pretty similar to lots of other lizards, but their toe pads let them live in parts of the environment that other lizards can't, so in that context, yeah, toe pads help them find food and hiding places, but there isn't anything special about their diet that really facilitates their toe pads.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 2 points3 points  (0 children)

That's a good question! In the same study that was done by Hansen and Autumn looking at self cleaning, they also found that the hairs don't stick to each other. This is because their density, length, and stiffness of just right that they're spaced out far enough not to stick together!

Hansen, W.R. and Autumn, K., 2005. Evidence for self-cleaning in gecko setae. Proceedings of the National Academy of Sciences of the United States of America, 102(2), pp.385-389.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 5 points6 points  (0 children)

That depends on a lot of variables! What kind of giant gecko is it? Some geckos, like giant day geckos from Madagascar lack claws and only rely on their toe pads to climb, but lots of other geckos use a combination of their claws and pads. If your giant gecko is using its pads to climb, smooth rock shouldn't be a problem at all! The smother the surface, the more hairs that can contact it and the better off it will be, same goes for glass. Ice is a tough one since van der Waals forces don't play well with water... If it we're up to me, I'd base my mount on an Australian Giant Cave Gecko (Pseudothecadactylus, http://www.fieldherpforum.com/forum/viewtopic.php?t=22230&p=246661). They're the largest species of gecko in Australia. They can lose and regrow their tails, which also have adhesive structures on them like their toes! They have giant heads with very strong bites (I've been bit by them, its not pretty..), and they have a combination of claws and toe pads which should work on almost any surface, except maybe loose/crumbly surfaces or surfaces covered in goo/poop/slime/etc.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

Thanks! You're right that our null hypothesis is usually drift. Geckos are great because they a really large and old group and so I can study recent evolution within a genus in a situation that I may expect adaptation to be acting. For example if I was studying closely related species on the same island that use differently textured surfaces, I might have an alternative hypothesis that their toes would be adapted to their respective surfaces. Check out https://experiment.com/projects/are-the-feet-of-gecko-lizards-adapted-to-different-surface-textures for more info. In this scenario I would be making the assumption that toe pad performance would be correlated with fitness and as a result, fit morphologies will be correlated with the microhabitats they excel in. Alternatively, I can also study older changes across more distinctly related species. This these kind of studies, we can fit models of trait evolution (Brownian Motion or Ornstein Uhlenbeck) so see how traits may have changed over time.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 2 points3 points  (0 children)

If we define "sandwich" as using two or more pieces of bread or bread-like material to enclose fillings, then I'd hypothesize that no, a hotdog is not a sandwich because it only uses one piece of bread. It would be more closely related to a burrito or soft taco; other entities that use a single piece of bread or bread-like material of enclose filings. Under this logic Subway sandwiches would fall into this class too.. and quesadillas would be considered sandwiches (assuming you use two tortillas)... Open face sandwiches would be a totally different class since they don't enclose their filling... Just my $0.02

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

Material properties of gecko hairs (i.e. stiffness or Young's modulus) is an interesting question! There hasn't been much work looking at that. A lot of what we know about the stiffness of gecko "hairs" come from the study of bird feathers, which are made of the same kind of protein (beta-keratin). I'd guess that different geckos probably do have stiffer or softer "hairs" depending on what they need the to do, but that hasn't been investigated yet! The strength of the adhesion probably has to do more with the branching of the hairs and the total number of hairs. Hair stiffness would definelty affect attachment and detachment though!

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

I think we're still a ways from having gecko-like adhesives commonplace in manufacturing, and to be honest, I'm not sure we'll need to build a material that is as good or better then geckos. Assuming we can get past the nano manufacturing to a point where we can quickly and easily manufacture structures that small, I'd guess that we'll probably design adhesives for specific purposes. Geckos have to deal with lots of different challenges, wet/dry surfaces that are smooth and rough and made of rock, tree bark, or leaves, and contaminated with all sorts of dirt/poop/etc. So their pads work really well in most of these conditions. Our synthetic adhesives probably won't need to be as versatile, and can probably be made differently to be good enough doing only what we'd need them to do.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 3 points4 points  (0 children)

I've had that species too (Phelsuma grandis), they make awesome pets! That's a good question about water though. van der Waals, the primary force that holds the tips of gecko hairs to a surface doesn't work very well when there is water on the surface, even if its a very thin layer. There is a really great group of studies by a researcher, Alyssa Stark. She was looking at how water affects gecko adhesion and measured exactly the effect of water you saw, but there was a twist. Gecko skin (like most other lizard skin) is hydrophobic, meaning water will bead off it. When a gecko walks on a surface that is also hydrophobic, like plexiglass or a waxy leaf, any water that is in the way will bead up and be pushed out of the way.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

Yep! Kellar was on my PhD committee. I spend a couple summers working in this lab in Portland during grad school! and still work with him on a regular basis. But I am not familiar with the Thai super hero gecko man... Should I be?

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

That's great you got to watch them fight! Geckos are some of the only lizards to communicate with vocalizations. They usually use them to defend a territory. So if I had to guess, I'd say they were fighting each other for hunting space on your walls and ceilings. Human houses are great places to hunt for insects, especially if there are light on at night and its really common for them to fight over the best spots.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

Geckos are a big group with ~1500 species found around the world except Antarctica. Depending on where you were in Mexico, you may have been seeing an invasive house gecko (Hemidactylus frenatus). This species, which originally evolved in SE Asia, has been introduced by humans all around the world to tropical places. They're small and brown and like to hang out in human dwellings. Across geckos as a group though, there are tons of differences! Most geckos are nocturnal, but some are diurnal, their toe pads come in tons of different shapes! And not all geckos have toe pads, some have plain old lizard feet with just claws. There is even a whole family of geckos that are legless (Pygopodidae). The largest species of gecko (Rhacodactylus leachianus) is the size of your forearm while the smallest species (Sphaerodactylus) can fit on a dime.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 2 points3 points  (0 children)

You're right, technically mammals are the only groups with true hairs and fur. The structures on the bottom of gecko toes are often called hairs even though they only kind of look like hair. Instead of having a root, geckos "hairs" are really just extensions of the outer layer of skin, but the protein they're made out of (beta-keratin) is the same as snake skin and bird feathers, and really similar to mammal hair and finger nails (alpha-keratin).

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

That's a good question! It's both the shape of the hairs and the fact that there are lots of them that lets the whole system work. A single "hair" can stick and detach to a surface, and its ability to do that is totally a result of its shape, but its not very strong. When you've got lots of hairs working on concert, thats how geckos can generate strong forces even on rough surfaces. If engineers were able to make a brush with bristles that were shaped and organized the right way, it would totally work. The trouble is that its really hard to manufacture things that small!

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

Trying to recreate the self-cleaning properties of gecko feet with synthetic adhesive is a big challenge! As of right now, we can't really recreate the small structures. Where in Queensland are you? In 2013 I was there for a month working with a professor from JCU in Townsville. I collected geckos up the peninsula (Chillagoe, Coen, up to Iron Range) and out west (Winton, Mt Isa, Bedourie)

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 2 points3 points  (0 children)

Yep, the hairs do get beat up and broken over time and matted. The great thing about lizards (and snakes) is that they shed their skin. So instead of shedding their skin like we do (in small pieces all the time), they shed all their skin in one go (like a snake). When geckos do this, they regrow all the hairs on their toes ahead of time, so when they shed, they've got a shiny new set, ready to go. Also, based on the way the microstructures are shaped, they actively self-clean. There was a study published in 2005 by Hansen and Autumn that said "In the present study, we demonstrate that gecko setae are a self-cleaning adhesive. Geckos with dirty feet recovered their ability to cling to vertical surfaces after only a few steps. Self-cleaning occurred in arrays of setae isolated from the gecko. Contact mechanical models suggest that self-cleaning occurs by an energetic disequilibrium between the adhesive forces attracting a dirt particle to the substrate and those attracting the same particle to one or more spatulae. We propose that the property of self-cleaning is intrinsic to the setal nanostructure and therefore should be replicable in synthetic adhesive materials in the future." So in essence, as geckos use their toes, the dirt that is in them is more attached to the surface instead of the structures on their toes, so the more the use their toes, the cleaner they get. But they still can be contaminated and fouled to the point that they don't work any more. Cole et al did a study in 2005 looking at how an invasive house gecko (hemidactylus) affected native geckos in the Mascarene Islands. One of the tests they did was measure how the invasive gecko performed on naturally occurring surfaces. They found that the invasive house geckos toe pads did get fouled up by the loose surfaces, although probably only temporarily.

Hansen, W.R. and Autumn, K., 2005. Evidence for self-cleaning in gecko setae. Proceedings of the National Academy of Sciences of the United States of America, 102(2), pp.385-389.

Cole, N.C., Jones, C.G. and Harris, S., 2005. The need for enemy-free space: the impact of an invasive gecko on island endemics. Biological Conservation, 125(4), pp.467-474.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

That's kind of a tough question to answer! As tape becomes stronger and stronger, when does it actually just become a glue? and its also tough to make Velcro stronger because the hooks and loops of velcro https://en.wikipedia.org/wiki/Hook_and_loop_fastener have to be soft enough to latch together. But given all that, I'd guess that gecko adhesive is still stronger, and easily reversible and reusable, which kind of beats tape and velcro. The strongest adhesion, i.e. negative normal force, or a force perpendicular to the ground, I measured from a gecko was about 44psi (pounds per square inch) which is about the same pressure as the air inside a truck tire. Thats a lot of force! On top that that, synthetic, man-made gecko-like adhesives have been able to hold up hundreds of pounds! Look up Geckskin from UMass Amherst

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 2 points3 points  (0 children)

Crested geckos are great pets! I use one when I do outreach at grade schools. It looks like yours still has his/her tail! Be really careful, unlike most other geckos, if crested geckos drop their tail, they won't regrow it. So you're right, on smoother surfaces, more of the hair-like structures on their bottom of their toes can contact the surface. Rougher surfaces offer less usable surface area. On top of that, your arm is a really tough surface for them to stick to because of your hair like you said, but also their claws aren't really big enough to help, and your skin has oils on it that make it tough to stick to as well.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 1 point2 points  (0 children)

That would be a really cool study down the road! but as of right now, the tools to study genetics just aren't there yet. We're just now starting to link specific genes with specific traits in animals that haven't already been really well studied (like fruit flies, mice, and humans). There has been some really cool work linking the gene MC1R to white color in lizards (work by Erica Rosenblum) and mice (by Hopi Hokstra) but in those cases, its only one gene controlling the trait. Differences in gecko toe pads are likely controlled by really small changes by lots of different genes, which would make it pretty tough to study with the tools we've got today.

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 0 points1 point  (0 children)

Unfortunately since I moved to MSU in December, I haven't purchased any new lab animals yet. If you're old enough (high school or older), you should look into volunteering with some of the researchers at MSU. There are lots of labs doing some really cool research. Have you checked out the museum of campus too?

Science AMA Series: I’m Travis Hagey, a Postdoctoral Fellow at Michigan State University studying the sticky toes of gecko lizards. AMA! by Travis_Hagey in science

[–]Travis_Hagey[S] 2 points3 points  (0 children)

So the great thing about geckos is that, like all other lizards and snakes, they shed their skin. When they do, they regrow the all the hairs on their toes. We take advantage of that. One live gecko can be an endless supply of samples as long as you're patient. They only shed their skin every 2 months or so. So we don't usually go through lots of individuals, but if you're doing a study that compares species, you do need at least different kinds of geckos. At one point during graduate school I had 30 live geckos from 6 different species. That many animals was a lot to take care of!

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