Evolution of variation in reproductive morphology and behavior


The ritualized courtship behavior of plethodontid salamanders has served as a productive system for investigations of the evolution of complex behaviors and prezygotic reproductive barriers, but most research focuses on a small number of species. 


Through opportunistic fieldwork, my colleagues and I published observations on several poorly-studied species (e.g., Pierson et al. 2017; Pierson et al. 2018), and with behavioral, genomic, cytogenetic, and field observational data, we have characterized dramatic variation in male secondary sexual characters and correlated reproductive behavior in the two-lined salamander (Eurycea bislineata) species complex. Our first publications describing alternative reproductive tactics in Eurycea were recently published in The American Naturalist (Pierson et al. 2019) and Herpetological Review (Pierson 2019).

Reticulate evolution, secondary contact, and hybridization

Speciation is often neither instantaneous nor permanent, and the advent of genome-scale data has enabled scientists to infer reticulate evolutionary histories. I use phylogenomic and population genomic methods to better understand how ancient and modern hybridization structure genetic diversity.


My work focuses on the two-lined salamander (Eurycea bislineata) species complex, which are among the most widespread and abundant amphibians in the eastern United States. Previous studies have shown the importance of river drainages for its phylogeography, and our new data reveal the complex interplay between large-scale geological change (e.g., drainage reorganization) and fine-scale ecological differences in structuring genetic diversity. I also collaborate to apply similar methods to uncover the evolutionary history of other amphibians, such as woodland salamanders (Plethodon; Felix et al. 2019) and Brazilian frogs (Physalaemus; Nascimento et al. 2019). 


Developing and using molecular tools to study natural history


Natural history observations fuel biological inquiry. As our scientific toolbox grows in size, the kinds of questions we can ask--even about basic natural history--change. With undergraduate and citizen scientist collaborators, I am using genetic and genomic techniques to better understand the natural history of amphibians.


For example, my colleagues and I have developed environmental DNA (eDNA) methods to study amphibian communities in the Southern Appalachians. Species-specific qPCR assays have proven effective for locating rare species (Pierson et al. 2016), and NGS metabarcoding gives us the ability to characterize entire communities (Glenn et al. 2019). Citizen scientist volunteers at the Great Smoky Mountains Institute at Tremont are leading the charge on implementing this technique; click here to learn more. Recently, we have also been developing and using molecular techniques to study the diets of amphibians.

© 2019 by Todd W. Pierson