May
9
Lizards in Hurricanes
“Extreme climate events are intensifying due to climate change and may represent overlooked drivers of biogeographic and large-scale biodiversity patterns.” — Colin Donihue et al.
When I first moved from New Jersey to Florida several years ago, one of the things I found hardest to get used to — moreso even than palm trees and lack of snow in the winter — was the virtually ubiquitous anole. These little lizards could be seen skittering across sidewalks and driveways, crawling up-n-down windows and treetrunks, etc. Sometimes, one needs to watch where one is walking lest s/he step on an anole with a particularly bad sense of timing.
But, they’re harmless to humans and eventually I got used to them. (Plus, they eat pest insects.) In fact, when one finds its way into our sunroom, I typically name it something like “Mr. Green” or “Ms. Brown” — not my most creative, but I do like to add a personal touch as I chase the lil critter and try to coax it into the “relocation net”.
When I mentioned things to get used to in Florida, you might have thought of hurricanes, since we get our fair share of them down here. Have you ever wondered where the wildlife go to take shelter from a hurricane? I have. (Well, not often, but I have.) I suppose some have hidey-holes or can burrow into the ground, but what about, say… anoles? I actually read a brief article about this last year.
An international, crossdisciplinary research team set out to figure out what anoles do in such situations. According to biologist Colin Donihue, lead author of the resulting paper published in the PNAS:
“We got a leaf blower set up, and we filmed these lizards as they reacted to those hurricane-force winds. The lizards consistently reposition themselves around the perch so that they’re in the lee. A lot of the time, their back legs would get thrown off and they’d hold on with just their front legs.”
The team took their research “on the road” to Turks and Caicos initially, following the aftermath of a couple hurricanes. They later sought out nearly 200 anole species in locations ranging from Florida to Brazil. What they determined was that the anoles that survived hurricanes had consistently larger toepads (i.e., more surface area) on both forelimbs and hindlimbs than those that didn’t survive. The “directional shifts in morphology” were noticeable quite soon after the “extreme climatic event” and persisted 18 months later. That is, the populations maintained their now-larger average toepad sizes. (Neither the article nor abstract explained, but I suppose the alternative would have been that the increased toepad size was a stress-induced but temporary feature that subsided after things got back to normal.)
This continued into the next generation, so the team was excited to see “longer-term impacts” from such events. Then they tested within a single widespread species found on many Caribbean islands and across the range of the Anolis genus, in order to see “whether variation in hurricane history across space correlated with variation in toepad characteristics at two geographical scales.” Using 70 years of hurricane data, they determined that “[i]sland populations of A. sagrei that experienced more hurricanes have relatively larger toepads than those that experienced fewer hurricanes.” Then they looked across 188 Anolis species and saw that those which “experienced more hurricanes had relatively larger toepads on both forelimbs and hindlimbs.” (They also tested potential explanatory variables and found no significant correlations with toepad area.)
So, when it comes to anole survival rates in hurricanes, it would seem that toe size — and, thus, grip strength — matters considerably.
The research team mentions a few areas for further investigation (mostly regarding habitats and physiological traits other than toepads) but are quite pleased with the results of their study, which they believe “demonstrates that extreme climate events can have enduring evolutionary impacts that transcend phylogenetic and geographic scales.”
This all seems to be a clear example of natural selection. But, one particular question comes up that I wanted to mention — i.e., how big can these anole toepads get? If we assume a Darwinian paradigm (as the research team does), those toepads could potentially keep getting larger and larger, resulting in… what? New species? New genera? Something even more drastic? But, Donihue raises a valid concern:
“There must be a tradeoff between having big toepads during a hurricane and not having absolutely massive toepads that are so big you can’t really be a good lizard. When I talk about being a good lizard, I mean having traits that give you an advantage in all the things you need to survive. Those traits aren’t necessarily the same as those traits that help you survive in a hurricane.”
He’s right. At some point, much bigger feet will end up being a disadvantage during day-to-day survival. These are the same sort of concerns that engineers have when designing things. In this world, at least, not every feature or trait can be “ideal” at the same time. Optimal designs require tradeoffs. But, of course, evolutionary processes don’t “design” anything. Also, the paper doesn’t mention any extant species that already exhibits huge feet. So, if there is indeed a natural limit on toepad growth, what instituted that limit in the anole’s genetic makeup? Or, what conditions occurred in anole history that resulted in limiting toepad size to a presumably optimal range?
Obviously, I’m not questioning natural selection, and we’ve seen the same type of smale-scale adaptations in things like the Galápagos finches and cichlid fish in Africa. Also, as Michael Behe has pointed out, these adaptations involve breaking or losing existing genes, which makes evolution self-limiting. (Note the “pathetic blunted wings of flightless cormorants on the Galápagos”, for example.) Rather, I’m questioning the limits of evolutionary change.
Yes, I realize this is a tiny part of a much bigger discussion. No, I’m not an expert. However, I do submit that Intelligent Design is as good or better an explanation for these things than blind, mechanistic evolution.
Also,… anoles are kinda cute!
