Bob Cox is currently raising multiple generations of brown anoles as part of a controlled breeding experiment in his lab at the University of Virginia. In collaboration with Bob and several other researchers, I am measuring the thermal sensitivity of sprint speed in hundreds of these animals. Because we know how each animal is related to each other, we can quantify both the heritabilities and genetic correlations underlying different components of thermal performance.
Even if climate change serves as an agent of selection on natural populations, those populations will not evolve unless the traits under selection can be passed from parents to offspring. That is, for a population to evolve in response to environmental change, the traits which confer an adaptive advantage in the new environment must be heritable. For a trait to be heritable, it must have a genetic basis.
Although we have documented strong natural selection on the thermal performance traits in wild lizard populations, we currently do not know whether these traits are heritable. And even if they are heritable, that is not the end of the story. They may also be genetically correlated in ways that resist evolutionary change. For example, individuals that perform best at warmer temperatures might also have higher-than-normal absolute performance capacity (this phenomenon is referred to as the 'thermodynamic effect' or the 'hotter-is-better' hypothesis). Additionally, a specialist-generalist trade-off may occur whereby an individual can either perform very well over a small range of temperatures or non-so-well over a broad range of temperatures (a negative correlation between maximal performance capacity and performance breadth). A species' evolutionary response to climate change could depend critically on whether these correlations are found at the genetic level.
Despite its extreme importance for evaluating the vulnerability of organisms to climate change, the genetic architecture underlying a full thermal performance curve has never been elucidated for a vertebrate. We are currently attempting to remedy that knowledge gap by raising hundreds of brown anoles (Anolis sagrei) in a common garden experiment at the University of Virginia. Robert Cox (University of Virginia), Don Miles(Ohio University),Joel McGlothlin (Virginia Tech), and I are measuring the heritabilities and genetic correlations underlying preferred temperature and the thermal dependence of sprint speed in these animals. We are combining this quantitative genetic information with our estimates of selection measured in the field to predict the evolutionary trajectories of brown anoles as climate change progresses. Our primary goals for this project are to establish whether the thermal performance curve is heritable and to determine whether genetic correlations are more likely to hasten or constrain adaptation to changing thermal environments.
In collaboration withSusana Clusella-Trullas andIngrid Minnaar in South Africa, I am measuring the genetic architecture of the thermal sensitivity of walking speed in the invasive harlequin ladybug (Harmonia axyridis) and the native lunate ladybug (Cheilomenes lunata). The goal of this project is to evaluate the relative evolutionary potential of invasive versus native species under climate change, and to use those potentials to model the dynamics of competition in a warming world.