Parallel evolution and vicariance in the guppy (Poecilia reticulata) over multiple spatial and temporal scales
studied model systems present ideal opportunities to understand the relative roles of contemporary selection versus historical processes in determining population differentiation and speciation. Although guppy populations in Trinidad have been a model for studies of evolutionary ecology and sexual selection for more than 50 years, this work has been conducted with little understanding of the phylogenetic history of this species. We used variation in nuclear (X-src) and mitochondrial DNA sequences to examine the phylogeographic history of guppy populations across the entire natural range, and to test whether patterns of morphological divergence are a consequence of parallel evolution. We used phylogenetic, nested clade, population genetic and demographic analyses to investigate patterns of genetic structure at several temporal scales, in relation to vicariant events, such as tectonic activity and glacial cycles, shaping northeast South American river drainages. Our mtDNA phylogeny defines four major lineages, each associated with one or more river drainages, and analysis of molecular variance (AMOVA) also shows geographic structuring among these river drainages in an evolutionarily conserved nuclear (X-src) locus. Nested clade analysis (NCA) and other demographic analyses suggest that the east Venezuela/west Trinidad region is likely the center of origin of P. reticulata. Parallel upstream/downstream patterns of morphological adaptation in response to selection pressures reported in Trinidad rivers appears to persist across the natural range. Our results together with previous studies suggest that although morphological variation in P. reticulata is primarily attributed to selection, phylogeographic history may also play a role.
