EVOLUTIONARY AND HISTORICAL ANALYSIS OF PROTEIN VARIATION IN THE BLOTCHED FORMS OF SALAMANDERS OF THE ENSATINA COMPLEX (AMPHIBIA: PLETHODONTIDAE).

Abstract

Geographic variation in 23 to 29 protein-encoding genetic loci was examined in 48 populations of the Ensatina complex, a "ring species" distributed around the Central Valley of California. The samples span two critical links in the chain of morphologically distinct units: the transition from the unblotched to blotched color pattern types in the vicinity of Lassen Peak, northeastern California, and a geographic gap in the range of the complex in the San Gabriel Mountains, southern California. A general pattern of isolation by distance with a regular buildup of genetic distance correlated with increases in geographic distance characterizes the populations studied, with the exception of a little-differentiated group of populations in the northern Sierra Nevada; this region is postulated to be a zone of genetic reticulation characterized by relatively high gene flow. An adaptively significant color pattern is thought to have spread into the northern Sierra Nevada from the south, but protein variants have been introduced both from the north and the south. Genetic distances across the San Gabriel Mountain gap match expectations from the pattern of buildup of genetic distance as a function of geographic distance elsewhere in the complex. A phylogenetic analysis of the protein data supports the reticulation hypothesis; whereas the southernmost populations currently do constitute a monophyletic assemblage, an "extinction experiment" demonstrates that the distinction could be the result of the recent extinction of populations in a present gap in our sampling. The Ensatina complex appears to be a dynamic entity representing several stages in the evolution of species. It is a ring species, and whereas various taxonomic arrangements are possible, no taxonomic changes are proposed.