Dissertation Research: An Experimental and Genetic Analysis of Two Salamander Contact Zones: Adaptive, Biogeographic, and Systematic Implications

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

0072869 Wake and Kuchta Contact zones, where biological lineages once geographically separated come back together, are windows to the evolutionary process that enable the study of diverse evolutionary phenomena. Graduate student Shawn Kuchta, under the direction of Dr. David Wake, will use molecular techniques and field experiments to study two cryptic contact zones in two unrelated salamander taxa. In the Ensatina eschscholtzii (Caudata: Plethodontidae) complex, two distinct subspecies (oregonensis and xanthoptica) contact in northern California. An earlier detailed analysis of color pattern characterized the interaction as broad intergradation, but new molecular data suggest a tight genetic border. The hypothesis under test is that the "intergradation" of color pattern is introgression across a hybrid zone because the xanthoptica color pattern is a potential mimic of the extremely toxic newts of the genus Taricha. The contact zone between oregonensis and xanthoptica will be characterized genetically using mitochondrial (mt) DNA molecular sequence data, allozymes, and Restriction Fragment Length Polymorphisms (RFLPs) of nuclear DNA. Tests of bird predation will employ clay models in field experiments designed to test the possibility of a mimicry system between xanthoptica and Taricha. The second contact zone is located in the southern Sierra Nevada, where two clades of the California Newt, Taricha torosa, contact. This border is truly cryptic: it appears that T. torosa from the coast ranges colonized the southern Sierra Nevada, then acquired the phenotypic characteristics of Sierra Nevada populations. The causes of this phenotypic shift are unclear. Nuclear and mtDNA markers will be used to characterize the contact zone, and to investigate the cause of the phenotypic evolution of the southern Sierra Nevada populations. Both of these studies are grounded in population-level phylogenetics and an empirical approach to the study of species formation and differentiation.