Molecules, morphology, and area cladograms : a cladistic and biogeographic analysis of Gambusia (Teleostei: Poeciliidae)

Abstract

Researchers investigating historical biogeography rely on taxon cladograms to infer the relationships of different areas of endemism. Unfortunately, systematists are often faced with many equally parsimonious taxon cladograms from a single data set or conflicting phylogenetic hypotheses from independent data sets. We present an analysis of congruence between two conflicting phylogenetic hypotheses of the poeciliid fish genus Gambusia, one based on mitochondrial DNA sequences and the other based on morphological characters. We explore how different phylogenetic hypotheses alter interpretations of area relationships and propose a set of area relationships for the genus. Furthermore, we compared the area relationships depicted for Gambusia with that of two Middle American fish genera (Xiphophorus and Heterandria) with similar distributional limits. Our analysis revealed areas of congruence among taxa from nuclear Central America but areas of incongruence among taxa from the Panuco basin and North American components. We discuss the implications of our findings in light of conventional hypotheses regarding Caribbean biogeography. This study illustrates the importance of considering alternative phylogenetic hypotheses fully before attempting to interpret the biogeographic history of a taxon or region.