Behavior determines how organisms interact with their environment, and has long been posited as a pacemaker for evolutionary diversification. The classical view is that behavior drives evolution by exposing organisms to new selective pressures. Behavior can also restrain evolutionary change. The ?behavioral inhibition? hypothesis suggests that some behaviors, such as thermoregulation, helps organisms maintain a constant selective environment, obviating the need to adapt even in the face of changing environments. This research tests the idea that a single behavior (perch use) can simultaneously impede physiological evolution while impelling morphological evolution in Anolis cybotes. This species is found in different thermal environments, so the researchers expect that it will use behavior to maintain a constant body temperature. The researchers are using a replicated experiment to test this hypothesis, comparing habitat use, physiological, and morphological characteristics of A. cybotes in the Dominican Republic.
This research is the first empirical test of the idea that behavior can simultaneously impede and impel evolution in different traits. This study will provide an excellent example of evolution in action. The research will help show that, while natural selection drives evolution, it is behavior that mediates the selective environment. The authors will disseminate the results of this study to popular scientific articles, public lectures, scientific blogs, and museum exhibits. The results of this study will help inform policy makers and conservationists how species can mediate the thermal environment, and use these data in the light of climate change to protect species and their environments.
The goal of this research project was to determine the multifarious effects of organismal behavior on evolution. Specifically, I sought to test the hypothesis that behavior can serve to both impede and impel evolution in different traits. For this study I focused on the tropical lizard, Anolis cybotes, which is found on the Caribbean island of Hispaniola. On this island, A. cybotes ranges from mesic, tropical habitats near sea level to montane pine forests, where mean annual temperature is 15C colder, providing the opportunity for adaptation to different thermal extremes. I found that, despite inhabiting markedly different thermal environments, lizards at high elevation were able to maintain body temperatures comparable to lizards near sea level. Specifically, lizards at high elevation bask more frequently and are nearly always observed on rocks, rather than vegetation. Near sea level, in contrast, lizards are more often found using vegetation and perching in the shade. Through physical modeling, I was able to determine that trees are the thermally most suitable perch at low elevation, as rocks are nearly always lethally hot. In contrast, trees are nearly always too cold at high elevation, and rocks are the only perch that get suitably warm for lizards to effectively thermoregulate. Thus, the use of trees at low elevation and rocks at high elevation confers a distinct thermoregulatory advantage for lizards. In addition to similar body temperatures, lizards at high elevation possess similar thermal physiologies to their low elevation counterparts. Lizards from high and low elevation populations possess similar preferred temperatures (Tp) and critical thermal maxima (CTmax). These measure correlate with an organism's performance ability. Thus, I found that thermoregulation shields lizards from selection on physiology, and precludes physiological evolution. I then tested whether the switch to rocks at high elevation is leading to morphological evolution. I found that lizards at high elevation have flatter heads and shorter hindlimbs than lizards at low elevation. Through a common garden experiment I demonstrated that these morphological differences are genetically based, rather than due to plasticity. Thus, the same behavior - a perch switch to rocks at high elevation - simultaneously impedes physiological evolution while impelling morphological evolution. The possibility that behavior can influence evolution in different directions has been previously hypothesized, but until now remained untested.
