Abstracts Category : Other

Biogeography and Climatic Niche Evolution in the EasternRed-backed Salamander (Plethodon cinereus)

by Thomas P Radomski

Phylogenetic niche conservatism (PNC) is the retentionof ancestral ecological characteristics among related species, moreso than would be expected by a simple Brownian motion process. PNCmay be important in explaining biodiversity gradients, speciesranges, and species formation, but an ecological cause for PNC hasbeen challenging to identify. One hypothesis is that PNC occurswhen ecological opportunity (exposure to new, accessible nichespace) is lacking. Ecological opportunity may be unavailable whenhabitats are ecologically saturated, but conversely, theavailability of depauperate environments may provide opportunity.Because eastern Plethodon salamanders are characterized by strongPNC, studying a species within Plethodon characterized by nichelability may elucidate why PNC occurs. I investigated thebiogeography of the Eastern Red-backed Salamander (Plethodoncinereus) and tested the hypothesis that the climatic niche of P.cinereus diverged when glacial retreat made competitor-freehabitats available. I addressed this hypothesis by sampling 202individuals from 107 populations throughout the range of P.cinereus, and I analyzed molecular sequences for threemitochondrial and three nuclear loci, totaling 4,686 base pairs. Atime-calibrated phylogeny was inferred with the Bayesianphylogenetic program BEAST. Among intraspecific clades, I testedfor climatic niche divergence and compared rates of evolution usingclimatic data. I found that three different clades invaded areasnorth of the last glacial maximum (LGM), with one clade occupyingmost of the range beyond the LGM. Niche models and rates ofclimatic niche evolution were compared between clades. Consistentwith the ecological opportunity hypothesis, I found that the rateof climatic niche evolution was significantly greater forpopulations that colonized areas north of the LGM. This studyprovides an ecological explanation for PNC and its converse, nichelability, by examining the climatic niche in a phylogeographiccontext.Advisors/Committee Members: Kuchta, Shawn (Advisor).