Biogeography of the livebearing fish Poecilia gillii in Costa Rica: are phylogeographic breaks congruent with fish community boundaries?

One of the original goals of phylogeography was to use genetic data to identify historical events that might contribute to breaks among communities. In this study, we examine the phylogeography of a common livebearing fish (Poecilia gillii) from Costa Rica. Our goal was to determine if phylogeographic breaks in this species were congruent with previously-defined boundaries among four fish community provinces. We hypothesized that if abiotic factors influence both community boundaries and genetic structuring in P. gillii then we might find four clades within our focal species that were geographically separated along community boundary lines. Similarly, we expected to find most of the genetic variation in P. gillii partitioned among these four geographic regions. We generated DNA sequence data (mitochondrial cyt b and nuclear S7 small ribosomal subunit) for 260 individuals from 42 populations distributed across Costa Rica. We analyzed these data using phylogenetic (parsimony and likel...