Natural selection favors heat tolerant brown anole lizards on this baking hot peninsula in The Bahamas.
Global climate change may be the most profound physical change our planet has experienced in human history. As temperatures rise and extreme weather events become more frequent, life as we know it will have to adapt or face extinction. Given the dramatic impact that human beings are having on the planet, a major challenge of 21st century biology is to understand the how, when, and why of biological responses to rapid environmental change. A central question underlying much of my research is this: Can biological populations adapt to climate change?
Species are not totally fragile entities that passively go extinct as soon as their environment changes. Most populations contain phenotypic and genetic variation which can serve as the basis for evolutionary adaptation to changing environments. Evolution is typically thought of as a slow process, so the possibility that organisms could "use" evolution to mitigate the negative effects of climate change has been controversial. Nevertheless, in recent years it has become clear that populations can evolve much faster than we used to think, and this phenomenon has been dubbed "contemporary" evolution because it happens on observable time scales. I use large-scale field experiments to answer a number of questions related to this research program:
Which of the traits that are important for survival and reproduction in a warmer world vary within populations, and of those, which have a genetic basis? What are the specific genes that contribute to phenotypic variation and how are they distributed throughout the genome? When organisms use behavior to buffer themselves against changes in their environment, will natural selection be strong enough to drive rapid evolutionary change? More generally, how does behavioral mode (e.g. whether the species is a thermoregulator or thermoconformer) modify the strength and form of selection?
Will species need to rely on de novo mutation to generate the genetic variability needed for adaptation, or will standing allelic variation be sufficient?
I have conducted a number of field-based transplant experiments aimed at directly measuring the selective effects of rapid climate change. These experiments involved collaborations with Ryan Calsbeek(Dartmouth College) andRobert Cox(University of Virginia) for work done in The Bahamas, andSusana Clusella-Trullas(Stellenbosch University) for work done in South Africa. The idea behind these experiments is simple: Instead of trying to change the climate around the organism, we simply move the organism to a new climate. That way we can directly observe what happens when species are exposed to a sudden change in their physical environment.
Currently, I am setting up two long-term in situ evolution experiments on islands in The Bahamas and Panama. These projects are in collaboration with Jonathan Losos (Washington University), Christian Cox (Georgia Southern University), and W. Owen McMillan (Smithsonian Tropical Research Station). In both of these systems, we are transplanting populations of Anolis lizards to small islands that vary in their local thermal environment. We are identifying some of the genes that are important for thermal adaptation using genome-wide association studies, and then tracking the evolution of each population in real time across our experimental islands. These systems allow us to measure the interplay between natural selection and genomic change in wild populations experiencing a rapid change in their physical environment, as well as to explore the role of behavior in modifying evolutionary trajectories (Anolis sagrei in The Bahamas is an active behavioral thermoregulator whereas A. apletophallus in Panama is a thermoconformer).
In South Africa, southern rock agama lizards are adapted to rock outcrops that differ dramatically in climate. In the northern portion of their range, they experience hot and dry conditions, whereas in the southern portion of their range they experience cool and wet conditions.