Comparative phylogeography of livebearing fishes in the genera Poeciliopsis and Poecilia (Poeciliidae: Cyprinodontiformes) in central Mexico

Phylogeography relies on examination of geographical distributions of genealogical lineages (Avise, 2000), whereas biogeography relies upon concordant geographical distributions of multiple species (Briggs, 1974; Nelson & Platnick, 1981). However, just as biogeography depends on evidence from multiple species, inference about phylogeographical patterns can be strengthened by examination of multiple codistributed species (i.e. comparative phylogeography). Concordance of gene-tree partitions across multiple codistributed species implies that the same historical biogeographical factors (e.g. vicariance) have shaped intraspecific phylogenies (Avise, 2000). Evidence from multiple taxa is more relevant when the physical barrier responsible for a particular vicariant event is not conspicuous or the date of its appearance cannot be accurately determined. One such case is illustrated by the vicariant events caused by geological activity of the uplifted Trans-Mexican Volcanic Belt (TMVB) in central Mexico (Fig. 1). Tectonic and volcanic activity in the TMVB began in the early Miocene (c. 25 Ma; Ferrari et al., 1999), and apparently Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA