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Reproductive isolation is a precondition for two closely related taxa to reproduce successfully as separate entities and is the pillar of the Biological Species Concept. Hybridization and introgression are two biological processes implying incomplete speciation and are perceived as marginal in vertrebrates with fertiliziation via penile insertion (mammals, squamate reptiles). This study presents a multi-faceted approach, using molecular and morphological characters of two mostly parapatric watersnake species to analyze the dynamics of a massive organismal and genetic exchange within their contact zone, correlating it to different types of ecotonal transitions, exhibiting distinct habitat preferences and physiological tolerances between both taxa. Nontheless fixed nuclear genetic markers and the distinct environmental correlates reveal that the two taxa are independent entities and qualify as species under most species concepts, whereas hybrid superiority is limited to the interspecific ecotones. This book contributes relevant information to some persisting problems of species concepts and applies an integrated approach on a fascinating aspect of evolution.

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Konrad Mebert, 1964, Switzerland, global freelance biologist in conservation, population biology, natural history, biodiversity and evolution, M.S. at University of Zürich (biology), Ph.D. at Old Dominion University (hybridization) in Virginia, extracurricular work as a biomedical molecular biologist and environmentalist in the US

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