Research

Using experimental islands to understand rapid adaptation

We have transplanted thousands of Anolis lizards to dozens of islands in the Panama Canal (photo, left) and The Bahamas (four pics, below). Islands in both places differ in their biotic and abiotic environments such that populations are exposed to different selection pressures. We track these populations in real time with mark-recapture, and ask questions about adaptation to novel environments. Major questions include: How fast can morphological, physiological, and behavioral traits evolve when fitness landscapes change? What is the genomic basis of traits that are important to lizard fitness? What is the basis of phenotypic plasticity in gene expression, and does plasticity evolve in novel environments? How does natural selection impact population dynamics, and vice versa?

We transplanted populations of brown anoles (Anolis sagrei) to 17 islands in The Bahamas. As you can see from the pics to the left, they differ dramatically in habitat structure and substrate, and these translate into huge differences in thermal environments. We are studying how thermoregulatory behavior evolves on these islands, and whether changes in behavior result in subsequent physiological, morphological, and life-history evolution. We are also investigating the genomic basis of adaptation to these different island environments. This research is done in collaboration with Christian Cox, W. Owen McMillan, and Jonathan Losos.

Evolution in the face of gene flow

Most species display spatial structure. In other words, they are composed of populations that are isolated from one another to varying degrees. It is not well understood how partial connectivity between populations influences adaptation to environmental change. How do populations compensate for changing environments when they experience dispersal and gene flow from geographically distant places that may have different environments? We are studying the Dominican anole (Anolis oculatus; pic, top right) to understand how populations can persist and even thrive in divergent environments while experiencing ongoing gene flow. This species (pic, right) is the only endemic anole on the island of Dominica, and can be found in all of the available environments on the island. We find them in cool, wet cloud forests (first pic on the right) and hot, dry coastal forest (second pic on the right) where they regularly experience body temperatures that differ by more than 10°C! We are using reciprocal transplant experiments to understand how populations are able to adapt to these different environments in the face of gene flow.

Host-microbiome co-evolution
in a changing world

Most of the cells in the bodies of vertebrates are not their own. Instead, animals like lizards are covered and filled with billions of microbes (mostly bacteria). Many of these bacteria species have co-evolved with lizard cells to perform vital functions. Increasingly, researchers are studying how these "meta-organisms" evolve and interact with their environments. For example, it is likely that the gut microbiomes of ectotherms like lizards play a key role in the responses of populations to climate change, but the ways in which microbes mediate rapid adaptation in their animal hosts are almost completely unknown.

We have conducted several experiments aimed at understanding how a warmer, drier world might change the gut microbiome communities of slender anoles in Panama. We used greenhouse experiments (top pic, right) to determine the short term effects of warming on lizard gut communities, and have paired these with studies of the changing gut communities on the hotter experimental islands. We also found that gut microbe community composition changed dramatically in mainland populations after a record-setting drought that occurred during the dry season of 2019 (bottom pic, right).

In the near future, we plan to manipulate lizard gut microbiomes using antibiotics and fecal transplants to test how microbiome variation mediates lizard fitness on warmer versus cooler islands. This research is done in collaboration with Christian Cox and W. Owen McMillan and is currently being led by graduate student Claire Williams.

Sexual signal and behavioral evolution

Anoles have a colorful throat fan, called a "dewlap", which is usually much larger in males and that they use to attract females and to deter rival males and potential predators. Interestingly, slender anoles in Panama have a dewlap polymorphism (top pic on left), whereby some individuals have a solid yellow dewlap ("solid" morph; lizard on left) and others have white around the edge ("bicolor" morph; lizard on the right). This trait follows simple Mendelian inheritance with the solid allele being dominant to the bicolor allele, and there are naturally occurring populations with varying frequencies of each of these morphs.

We are transplanting both morphs to islands that vary in canopy cover to test the hypothesis that higher light levels reaching the understory select for darker dewlaps (see the picture of a canopy gap on one of our islands, left). We are tracking survival and reproductive success of each individual to determine how sexual and natural selection jointly determine the frequencies of dewlap morphs.

We are pairing dewlap studies with measurements of female choice, male boldness, and other components of behavior in an attempt to understand how whole suites of behavioral traits evolve when structural, climatic, and biotic environments change. This research is done in collaboration with Christian Cox, W. Owen McMillan, and John David Curlis.