Research
We apply a phylogenetic perspective to a variety of topics in evolution and ecology, using reptiles and amphibians as model systems. These topics include species richness, speciation, sexual selection, development and life history, community ecology, and morphological evolution. We also study the theory and methods of systematics.
Below is a sampling of some of the projects that we are working on presently.
Phylogeny, speciation, and species richness in Appalachian salamanders. Many of the worlds biodiversity hotspots are montane regions, but the reasons why montane regions are so rich in diversity and endemism has remained unclear. We are addressing this problem by focusing on a single group of organisms (plethodontid salamanders) in a single montane region (Appalachian mountains). The Appalachians appear to have the highest densities of salamander species of any region in the world. In collaboration with Paul Chippindale (Univ. Texas, Arlington), we are reconstructing the phylogenetic relationships of all ~100 species of plethodontids in eastern North America, using nuclear and mitochondrial markers. We will then combine our phylogeny with geographic and environmental data to understand the interaction of ecological and evolutionary processes that create high montane species richness and endemism. We are also studying the processes involved in specific speciation events, especially those that limit the distribution of montane endemics and might drive vicariance.
The Deep Scaly Project: resolving squamate phylogeny using genomic and morphological approaches. We are part of an NSF-funded multi-institutional consortium that is attempting to conclusively resolve the phylogeny of lizard and snake families. We are sequencing 50 single-copy nuclear protein-coding genes for 142 squamate species, and obtaining morphological data for the same species (as well as ~60 fossil taxa). We are seeking out new nuclear markers for vertebrate molecular phylogenetics through comparison of known nuclear genomes. We are also conducting simulation studies to address how phylogenetic information from fossils and large molecular data sets can be combined. Collaborators on this project include Tod Reeder, Jack Sites, and Maureen Kearney.
Dissecting the latitudinal gradient in species richness in treefrogs. One of the oldest known patterns in ecology and biogeography is the tendency for species richness to increase from temperate to tropical regions. Yet, a generally satisfying explanation for this pattern has remained elusive. The typical approach looks at the correlation between environmental variables and species richness, and considers evolutionary processes (e.g., speciation) only indirectly or not at all. We are focusing on one gradient in diversity in one group of organisms in one region (the change in hylid frog diversity from South America to North America), using an integrated phylogenetic approach that considers both ecological and evolutionary processes. We are reconstructing the relationships of the hylid species that make up this gradient using molecular and morphological data and then using this phylogeny to infer how ecological factors have influenced the diversity and distribution of species and clades to create the large-scale gradient in species richness. Collaborators include Tod Reeder, Bill Duellman, and Catherine Graham.
Evolution of color morph frequencies in Long Island redback salamanders. The classic model of speciation is as follows. A single homogeneous population becomes geographically divided, the populations diverge, and then the differentiated populations become sympatric again. We are studying a case where this scenario may have run in reverse. In most of northeastern North America, Red-backed salamanders (Plethodon cinereus) have two morphswithin a population, those with a red dorsal stripe (redback) and those without (leadback). On Long Island, however, most populations are monomorphic for one morph or the other, with redbacks dominating in the west and leadbacks in the east. We are currently using molecular markers and GIS-based analyses to try and uncover the evolutionary and ecological processess responsible for this remarkable situation.
