Reptiles and amphibians are cold-blooded!
This phrase has gone out of style in recent years because it's not true. There's nothing cold about their blood at all.
Reptiles and amphibians are ectothermic!
What's the difference? Because honestly in my head that's just a fancy word for cold-blooded.
It turns out that few amphibians and reptiles are at the mercy of the Weather Channel app on your phone. In fact we can remove this picture of a snake that operates at an internal temperature of 27F if it's 27F outside, or 100F internally if it's 100F outside. Instead it's better to think of ectotherms as creatures that must adjust their activity, behavior, and physiology according to the demands of the thermal environment to keep their body temperature within a range of functionality. Limiting exposure to suboptimal temperatures through thermoregulation is known as the Bogert effect. Marine iguanas, the only lizards that hunt in the ocean, display the Bogert effect by basking following foraging dives [1]. They have ~30 minutes in chilling waters to feed on seaweed before they quit by basking in groups on rocky ledges to maintain this range of functionality. There's some evidence that plethodontid salamanders seek out favorable microhabitats in the mountain forests to regulate temperature and moisture levels [2]. Lastly, Anolis lizards thermoregulate to maintain optimum internal temperatures of about ~26-30C despite up to 15C changes in the environment on any given day [3]. These are just a few of many adaptations to temperature tolerance by ectotherms. And it begs the question that many have asked, "Can ectotherms adapt to climate change?" It's a loaded question that might include some caveats if answered appropriately. But I think we should try to answer it. Some are. But right now, there's a lot more studies that predict where warming will be most pronounced and how that will affect species fitness in terms of local extinctions and range shifts. We have fewer far flung studies* to answer this question [4]. These studies help us understand how evolution takes place. We can use those really widely distributed species for our benefit by examining species at different points in time without actually going back in time. That's what Muñoz et al. did with Anolis lizards by examining montane versus lowland species. I think it's worth a shot in the context of climate change studies. Maybe everything is doomed, or maybe we'll find some adaptation and resilience where we might not expect it.
Citations: [1] The Marine Iguana, BBC Earth. https://www.youtube.com/watch?v=UDAutlF_aRY. [2] Farallo et al., (2018). [3] Muñoz et al., (2014). [4] Vitt, L.J., and Caldwell J.P., (2013).
*Far flung study: study of repeat sampling across environmental gradients of closely related species to answer questions of evolutionary time periods. These studies compare communities that have already adapted to particular habitats. Distance or other barriers are often considered proxys for time (i.e. communities that are continents apart would typically be considered longer evolutionary time periods than communities in adjacent states).
Great post! I actually read a paper in a class recently about the effects of urbanization on anole lizards. The results of the paper were that there was local adaption in behavior across the different landscapes (forested/urban). With that in mind, I wonder if going forward (for ectotherms) the main avenue for adaption will be through manipulation of behavior or through evolution of mechanisms of thermoregulation. Will we see less basking behavior? More heat avoidance behavior like shading? Or will we see ectotherms be able to tolerate these temperatures because of some mechanistic adaption that allows them to have a higher thermal minimum? Just some things that ran through my mind. Great post!
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