Current Research Projects

Our research explores the processes that generate and impact biological diversity with a focus on the mechanisms of rapid organismal change. We are particularly interested in both sides of the evolutionary speciation/extinction "coin" and specifically how changing environments impact these processes. Conceptually, our research addresses integrative questions with evolutionary, ecological, and conservation relevance. Methodologically, we favor an integrative genes-to-ecosystems approach and use techniques from functional genomics to field ecology. Two of our current projects detailed below address mechanistic questions about speciation and extinction in reptile and amphibian assemblages of the western US.


Lizard adaptation and ecological speciation

Understanding how quickly organisms can adapt to changing environments is a central goal of our research. In the Chihuahuan Desert of New Mexico, three lizard species exhibit striking variation in coloration associated with the geologically recent formations of White Sands. 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, and brown color morphs of all three species live on surrounding dark desert soils. Substrate matching for crypsis at White Sands has evolved in only a few thousand years and provides a replicated natural experiment to address important questions about rapid organismal adaptation and ecological speciation. We are particularly interested in factors that can accelerate rapid adaptation and speciation. In this system our research focuses on:

 

The genetic architecture of adaptation: The simple genetic basis of color variation at White Sands provides new insights into the genetics of rapid adaptation. Our research in this area focuses on comparing the genetic and functional basis of convergent adaptation across species. The convergent blanched phenotypes of lizards at White Sands have a similar genetic basis (i.e., mutations in the same gene) but a dissimilar functional basis (i.e., mutations halt melanin production in different ways). The similarities and differences across the White Sands lizards allow us to study the genetics of adaptation in a nature using a comparative framework. They also allow us to study the interplay between the genetic architecture of adaptation and demographic parameters like gene flow.

 

Behavioral consequences of adaptation: The rapid timescale for adaptive evolution at White Sands provides a rare opportunity to ask how morphological adaptation to novel environments can lead to changes in behavioral interactions. Our research in this area focuses on how natural and sexual selection interact during the early stages of ecological speciation. Specifically, color differences between lizard populations in New Mexico have led to changes in both intersexual interactions (i.e., mate choice) and intrasexual interactions (i.e., male-male territoriality). We therefore study the behavioral interactions between ecologically similar and dissimilar lizards to understand how local adaptation can alter intraspecific interactions and accelerate speciation.

 

Strength and dimensionality of selection: The White Sands system also provides an opportunity to studying natural selection in the wild. Ecological speciation is accelerated when natural selection acts on many traits simultaneously, and we are currently studying the multidimensional nature of selection at White Sands. We are conducting direct tests of natural selection in the wild and conducting functional studies of morphological traits other than color that have evolved quickly at White Sands (e.g., the effect of limb length on running speed). We hope that the comparative study of three evolutionary replicates will provide new insights into the predictability of adaptation in novel and changing environments.

 


Amphibian declines and emerging infectious disease

Infectious pathogens rarely drive their hosts extinct, but periodically highly virulent pathogens pose dramatic threats to human health, agriculturally important crops, or wildlife. Recent outbreaks of novel fungal pathogens have focused new attention on host-pathogen interactions and their response to environmental change. One such interaction is between the deadly chytrid fungus Batrachochytrium dendrobatidis (Bd) and its amphibian hosts. Amphibians around the world have been experiencing massive population losses and extinctions due to Bd, with hundreds of species infected. However little is known about the specific mechanisms of Bd virulence and frog susceptibility. This system provides opportunities to understand how new pathogens emerge and how hosts respond to novel disease agents. Further it provides an opportunity to assess how aspects of global change (e.g., climate change, invasive species, pollution, habitat alteration) influence disease dynamics. In this system our research focuses on:

 

Determinants of host susceptibility: The variation in host response to Bd provides an opportunity to study why some hosts are susceptible to emerging pathogens while others are resistant. Our research in this area focuses on using ecological, experimental, and genomic tools to understand host susceptibility to Bd. For example, we study Bd-resistant and Bd-susceptible frogs in nature, in the lab, and using functional genomics to determine the mechanisms by which Bd kills frogs and to understand why some species are more resistant to its deadly effects.

 

Mechanisms of fungal pathogenicity: The recent emergence of Bd provides a case study for understanding the rapid evolution of novel pathogens. Our research in this area focuses on using genomic tools to identify determinants of pathogenicity. Specifically, we conduct whole genome sequencing and gene expression studies to characterize the genomes of different Bd strains and close (non-Bd) chytrid relatives. This work allows us to identify putative pathogenicity factors.

 

Patterns of pathogen origin and spread: The mystery surrounding Bd's origin provides an opportunity to understand the interaction between pathogen evolution and other aspects of environmental change. We are using population genomics to answer persistent questions about Bd's origin and spread. We are also interested in understanding the role of climate change, invasive species, and the global amphibian trade in the Bd epidemic.



Other Projects

In addition to the core efforts in the lab, we are involved in a diversity of other projects around the world including studies of amphibians in Panama, snails in the Galapagos, and spiders in Australia. These projects are all linked by a shared interest in the core processes that influence biological diversity.