>>CK,
>>Have you seen the following paper?
>>
>>RF Hoyer
>>=================================================================
>>
>>Molecular Ecology (2008) 17, 1918–1929 doi: 10.1111/j.1365-294X.2008.03725.x
>>© 2008 The Author
>>Journal compilation © 2008 Blackwell Publishing Ltd
>>Blackwell Publishing Ltd Good species despite massive hybridization: genetic
>>research on the contact zone between the water snakes
>>Nerodia sipedon and N. fasciata in the Carolinas, USA
>>K. MEBERT
>>Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA
>>Abstract
>>Genomic markers generated with the amplified fragment length polymorphism method
>>revealed extensive, panmictic-like hybridization along the narrow contact zone between
>>the water snakes Nerodia sipedon and Nerodia fasciata in the Carolinas, USA. However,
>>asymmetric distributions of diagnostic markers between both species and low frequencies
>>of backcrossed hybrids with a high value of interspecific mixture infer selection against
>>certain genotypes. This is consistent with a pronounced genetic and morphological preponderance
>>of N. fasciata characters in the hybrid zone. Despite massive hybridization within
>>the contact zone, the existence of nearly fixed genetic markers and the potential inferiority of
>>certain hybrid genotypes support the species status of the two taxa and corroborate known,
>>but nondiagnostic differences in morphology and ecology. This study stretches the
>>applicability of species concepts to cases, where the genetic compatibility between two
>>closely related species is very high, yet, they still evolve and persist as independent entities.
>>Keywords: AFLP, hybridization, incomplete speciation, Nerodia fasciata, Nerodia sipedon, snake
>>Received 11 March 2007; revision received 8 January 2008; accepted 24 January 2008

Hi, Richard, I have not seen this paper. Apparently what it describes is not unknown. Interspecific hybrids do occur in nature, as DNA studies have revealed what morphological studies cannot. The wolf, for example, is known to interbreed with the coyote based on DNA studies. From the abstract, it seems that two closely related species have come into secondary contact and there is hybridization. And since the hybrids with features that are intermediate between the two parental species are maladaptive, there is strong selection against them. This is what is predicted by the Biological Species Concept. The BSC further suggests that since the hybrids are maladaptive, natural selection would favor the evolution of premating isolation mechanisms. Once these isolation mechanisms have evolved, then the incidence of interspecific hybridization will be much rarer. Apparently some researchers are not very familiar with the BSC, so many of the phenomena that are consistent with the BSC appear as new revelations to them.

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