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Phylogenetic analysis based on nuclear and mitochondrial DNA sequences was used to test the validity of morphospecies of catfishes of the family Astroblepidae inhabiting the southern-most limit of their Andean distribution in the upper Ucayali and upper Madre de Dios river basins. Population samples of morphospecies designated a priori on the basis of morphological features were further diagnosed by the presence of unique and unreversed molecular synapomorphies, thereby confirming species validity for seven of nine cases. Although each are distinguished by unique combinations of morphological features, two morphospecies (designated F and H) cannot be diagnosed on the basis of apomorphic changes in molecular sequence that did not also occur in other astroblepid morphospecies or outgroup taxa. Further, one morphospecies (species G) was recovered as nested within the assemblage of populations sampled from morphospecies F, whose morphological diagnosis does not involve unique or apomorphic characters. In contrast, the absence of corroborating molecular apomorphies for species H, otherwise recognized by distinctive and uniquely derived morphological characters, suggests a history of rapid divergence and insufficient time for fixation of genetic differences. Species sharing syntopic distributions were not recovered as sister groups, and in some cases species distributed in adjacent river drainage basins were not more closely related to one another than to species distributed in more distant drainages. Three independent instances were observed of sister-group relationships involving species distributed in both the Apurimac and Urubamba rivers (Ucayali drainage). These observations combine to suggest that the current distribution of astroblepid species in the southern region may have arisen via a complex history involving both divergence between and dispersal amongst drainage basins that is probably repeated numerous times throughout the Andean distribution of the group. © 2011 The Linnean Society of London.

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Zoological Journal of the Linnean Society

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