Research

Using experimental islands to understand rapid adaptation

We have transplanted hundreds of slender anole lizards (Anolis apletophallus) to more than 20 islands in the Panama Canal (photo, left). These islands 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. We are integrating research techniques across multiple disciplines to link natural selection on a wide range of phenotypes with changes in genotypes and to understand the dynamics of rapid adaptation from molecules to biological communities. This research is done in collaboration with fellow co-PIs Christian Cox and W. Owen McMillan. Current lab members Claire Williams and Catherine Grey are conducting research in this system.

Climate change and life history tradeoffs

Climate change, by altering the thermal landscapes in which ectotherms live, will change the ways in which both males and females optimize their approach to reproduction. This is because the costs and benefits of thermoregulatory behavior will change as local climate shifts. Thus, energy may have to be shunted towards behavior that maximizes thermoregulatory performance and adult survival and away from behaviors that maximize egg or hatchling survival. We are working to understand this process by comparing populations of western fence lizards (Sceloporus occidentalis) across an elevational gradient, as well as within populations at the territory-scale, in the Great Basin Desert. A part of this research also includes an investigation into the selective forces that may have driven the evolution of viviparity (live birth) in squamate reptiles. This work is led by current lab members Guillermo Garcia-Costoya, Akhila Gopal, and Noa Ratia.

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 as a signal (possibly to attract females or to deter rival males). 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). Wild populations of slender anoles can have both morphs present or be fixed for one morph. We have shown (collaborative work with Christian Cox, Carlos Arias, Jessica Stapley and Renata Pirani) that this dewlap polymorphism is a simple Mendelian trait with the solid allele dominant to the bicolor allele, and that the underlying locus is probably the transcription factor SIM1.

We have documented that the frequency of each morph varies with understory light level on the mainland in ways consistent with sensory drive, and we are further exploring the factors that affect dewlap evolution by transplanting both morphs to islands that vary in their light environments and tracking changes in morph frequency over time. We are also quantifying female choice and male display behavior in an effort to understand the mechanisms that link signal transmission in a given habitat to the reproductive success of individuals. This research is a collaboration with Christian Cox, W. Owen McMillan, John David Curlis, Beth Reinke, and Renata Pirani.

Microbiomes as mediators of rapid adaptation

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 hosts 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 are conducting experiments aimed at understanding how a warmer, drier world might change the gut microbiome communities of slender anoles in Panama, and how these changes might affect lizard health and fitness. We are using greenhouse experiments (top pic, right) in combination with longitudinal sampling on mainland Panama and field-transplant experiments to warm islands to understand both the short and long-term effects of environmental change on lizard gut communities, and how these changes might affect lizard fitness.

In the near future, we plan to manipulate lizard gut microbiomes using antibiotics and probiotics to determine which microbes strongly affect lizard thermal tolerance (among other traits) and to test how microbiome variation mediates lizard fitness on warmer versus cooler islands. This research is done in collaboration with Christian Cox, W. Owen McMillan, and Candace Williams, and is currently being led by lab member Claire Williams.

The evolution of "complex phenotypes"

Life history and behavioral traits often covary with metabolic rates along distinct axes. Individuals (and populations) tend to fall along slow-fast, shy-bold, and cold-hot trait axes, and their position on these axes is thought to be driven by variation in metabolic rates. Individuals with higher intrinsic metabolic rates often grow faster and have more offspring, are bolder, and have higher optimal temperatures for performance. Despite these documented patterns of trait covariation, little is known about the agents of selection that give rise to pace of life. We are measuring correlational selection on suites of life history, behavioral, and physiology traits in western fence lizards distributed across an elevational gradient in the Great Basin Desert of Nevada to begin to understand what causes the evolution of trait complexes. This work is being led by current lab members Akhila Gopal, Guillermo Garcia-Costoya, and Noa Ratia.

Improving methods for measuring climatescapes

Abiotic environments are changing rapidly across our increasingly human-modified planet. One of the core goals of modern biology is to accurately predict future effects of changing environments on wild animal populations. However, a major limitation in this endeavor has been our limited ability to properly quantify "climatescapes" (e.g. thermal, water, and wind landscapes) at spatial and temporal scales that are relevant to most organisms. Most animal diversity is represented by ectotherms that are smaller than 50 grams, and most of these species experience environments at sub-meter scales. How can we quantify and map these environments accurately, such that we can properly model the ways they will change and impact animals in the future?

Our lab is working on this problem across multiple fronts. We are developing and validating methods to build operative temperature models using 3D printing. These models are highly morphologically accurate, can be produced relatively cheaply after initial investment, and are reproducible across labs as 3D printing files can be shared. We are also using thermal drone photogrammetry to build highly precise, three-dimensional maps of thermal landscapes. Finally, we are developing data loggers and computational techniques that can map wind movement across a landscape in detail. Our goal is to develop methods that can be used by other research groups and conservation managers to understand local environments with unprecedented precision. This research is being led by current lab members Noa Ratia, Guillermo Garcia-Costoya, and Akhila Gopal.

Videos and images to the right:

1. 3D thermal map of one our field sites produced through "photogrammetry"---infrared images, taken by a drone flown along transects, that are then digitally stitched together to reconstruct the landscape (video made by Karla Alujevic and Guillermo Garcia-Costoya).

2. Karla launching our thermal imaging drone at one of our field sites in the Great Basin Desert.

3. X-ray view of our field-deployable wind speed/direction data loggers that were designed by lab member Noa Ratia.