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1 September 2009 Genetic Leakage After Adaptive and Nonadaptive Divergence in the Ensatina eschscholtzii Ring Species
Ricardo J. Pereira, David B. Wake
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The salamander Ensatina eschscholtzii is an example of a ring species in which extant intermediate stages of terminal forms have a nearly continuous range, offering replicated interactions at several stages of divergence. We employ a greatly expanded allozyme database and individual-based analyses to separate the effects of divergence time and gene flow to evaluate how gradual divergence of populations around the ring contributes to the development of reproductive isolation. Despite the high degree of genetic (D ≤ 0.39) and ecomorphological divergence observed in secondary contacts around the ring, reproductive isolation or rare hybridization is observed only at the terminus of the ring. Instead, in the secondary contacts sampled around the ring, hybrids are common and reproductively successful, enabling genetic leakage between parental genomes and the potential for genetic merger. Nevertheless, genetic admixture is geographically broad (<100 km) only in contacts between ecomorphologically similar populations (within subspecies). When divergence is accompanied by alternative patterns of adaptive divergence (between subspecies), zones of intergradation are narrower and affect populations only locally (>8 km). Diversification and consequent genetic interactions in Ensatina reveal a continuum between populations, ecological races, and species, where polytypic traits and high genetic differentiation are maintained without reproductive isolation.

© 2009 The Society for the Study of Evolution.
Ricardo J. Pereira and David B. Wake "Genetic Leakage After Adaptive and Nonadaptive Divergence in the Ensatina eschscholtzii Ring Species," Evolution 63(9), 2288-2301, (1 September 2009).
Received: 24 October 2008; Accepted: 1 April 2009; Published: 1 September 2009

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Adaptive divergence
gene flow
polytypic species
secondary contact
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