…Current Projects
Currently we have two major research foci in the lab that address mechanistic questions about speciation and extinction in reptile and amphibian assemblages in the western US:
Disease-related declines in amphibians
Amphibians around the world have been experiencing massive population losses and extinctions. Although these declines have been precipitated by a number of factors, the fungal pathogen Batrachochytrium dendrobatidis (Bd) is a devastating threat, infecting hundreds of amphibian species worldwide. Among the species affected by Bd is the mountain yellow-legged frog, Rana muscosa, in the Sierra Nevada Mountains. A window into disease impacts on wild species such as R. muscosa is afforded by the recent completion of whole-genome sequencing for the model frog species, Xenopus tropicalis.
Genetics of host/pathogen interactions: The primary thrust of our frog/chytrid work focus on understanding, from a whole-genome perspective, the genetic changes associated with fungal infection of frog hosts. From the host perspective, we use whole genome expression assays to identify genes that are involved in frog response to B. dendrobatidis under different conditions. We leverage whole-genome data for the model frog species Xenopus tropicalis to make much of our lab-based immunogenetics work possible. From the pathogen perspective, we use both comparative and functional genomics to study genes that may be involved in Bd pathogenicity under different conditions.
The biology of bizarre critters: We were involved in the initial whole-genome sequencing project for B. dendrobatidis at the Joint Genome Institute and are now sequencing whole-genomes of a number of additional Bd strains. The resulting sequence data will provide a wealth of information about the biology of this basal group of fungi and provide insight into the evolutionary origin and spread of this emerging pathogen.
Applying genomics to ecologically important questions: One of our major research aims is to integrate functional genomics and organismal biology by applying genomic data to questions in nature. We have an ongoing interest in developing large-scale genetic resources for non-model species and diverse collaborations to better tackle evolutionary questions in complex natural systems. In the frog-chytrid system this is exemplified by collaboration with ecologists and disease modelers to understand why different populations of R. muscosa experience different outcomes (ie, persistence vs decline) to Bd exposure.
Ecological divergence in reptiles:
Understanding the processes that contribute to diversification and speciation is a central goal of evolutionary biology. Recently renewed attention has been given to ecological modes of speciation, whereby natural selection leads to rapid divergence. We have been working on a system involving color variation that lends itself to testing predictions from ecological speciation models. Three lizard species exhibit striking variation in coloration associated with geologically recent formations in the Chihuahuan Desert. Blanched color morphs of the Little Striped Whiptail (Aspidoscelis inornata), the Lesser Earless Lizard (Holbrookia maculata) and the Eastern Fence Lizard (Sceloporus undulatus) inhabit the white gypsum dunes of White Sands, a melanic color morph of S. undulatus is found on the black basalt rocks of the Carrizozo Lava Flow, and brown color morphs of all three species are associated with the surrounding desert soils. Substrate matching for these small diurnal lizards is critical for avoiding visual predators. The phenotypic variation along this gradient of black to white provides complementary natural “experiments” which have occurred in the last 2,000-6,000 years.
The demography of local adaptation: Using multi-species and multi-habitat comparisons, we endeavor to understand how population demography can influence organismal response to natural selection and how, in turn, demographic histories can be shaped by natural selection. For example, we compare multiple species exposed to the same environmental gradient at White Sands and ask how species-specific attributes (e.g., dispersal capability, life history strategy) may affect phenotypic response to selection.
The genetic basis of coloration: To develop a more mechanistic understanding of how organisms adapt to changing environments, we study the genetic basis of reptile color variation. Much of this work has focused to date on the melanocortin-1 receptor gene (Mc1r) because of its key role in the pathway that produces melanin in vertebrates.
The interaction between natural and sexual selection: The potential for natural selection across environmental gradients to lead to reproductive isolation is often mediated by coincident evolution of ecological divergence and mating preference. We evaluate the potential for interaction of natural and sexual selection in this system by conducting field based mate-choice experiments and by studying color patches which lizards may use for intraspecific communication in addition to those used for crypsis.
Views from around the Lab - slide show
Here are a few images from the lab and field test slide show