Department of Biological Sciences, California State University, Chico, California 95929-0515; E-mail: email@example.com.
RAPID DIVERSIFICATION, INCOMPLETE ISOLATION, AND THE “SPECIATION CLOCK” IN NORTH AMERICAN SALAMANDERS (GENUS PLETHODON): TESTING THE HYBRID SWARM HYPOTHESIS OF RAPID RADIATION
Article first published online: 8 MAY 2007
Volume 60, Issue 12, pages 2585–2603, December 2006
How to Cite
Wiens, J. J., Engstrom, T. N. and Chippindale, P. T. (2006), RAPID DIVERSIFICATION, INCOMPLETE ISOLATION, AND THE “SPECIATION CLOCK” IN NORTH AMERICAN SALAMANDERS (GENUS PLETHODON): TESTING THE HYBRID SWARM HYPOTHESIS OF RAPID RADIATION. Evolution, 60: 2585–2603. doi: 10.1111/j.0014-3820.2006.tb01892.x
- Issue published online: 8 MAY 2007
- Article first published online: 8 MAY 2007
- Received March 7, 2006. Accepted September 12, 2006.
- reproductive isolation;
Abstract The history of life has been marked by several spectacular radiations, in which many lineages arise over a short period of time. A possible consequence of such rapid splitting in the recent past is that the intrinsic barriers that prevent gene flow between many species may have too little time to develop fully, leading to extensive hybridization among recently evolved lineages. The salamander genus Plethodon in eastern North America has been proposed as a possible example of this scenario, but without explicit statistical tests. In this paper, we present a nearly comprehensive phylogeny for the 45 extant species of eastern Plethodon, based on DNA sequences of mitochondrial (two genes, 1335 base pairs) and nuclear genes (two genes, up to 3481 base pairs). We then use this phylogeny to examine rates and patterns of diversification and hybridization. We find significantly rapid diversification within the glutinosus species group. Examining patterns of natural hybridization in light of the phylogeny shows considerable hybridization within this clade, including introgression between species that are morphologically distinct and distantly related. Reproductive isolation increases over time and may be very weak among the most recently diverged species. These results suggest that the origin of species and the evolution of intrinsic reproductive isolating mechanisms, rather than being synonymous, may be decoupled in some cases (i.e., rapid origin of lineages outstrips the “;speciation clock”). In contrast to the conclusions of a recent review of adaptive radiation and hybridization, we suggest that extensive hybridization sometimes may be a consequence, rather than a cause, of rapid diversification.