Population structure of guppies in north-eastern Venezuela, the area of putative incipient speciation
1 Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, Krakow 30-387, Poland
2 Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada
3 Department of Biology, University of Victoria, Victoria, British Columbia V8W 2Y2, Canada
4 Centro de Ecología, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020-A, Venezuela
5 Laboratoire d’Ecologie Alpine, UMR 5553 CNRS-Université Joseph Fourier, BP 53 2233 Rue de la Piscine, Grenoble 38041, France
6 Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
7 Institute of Environmental Biology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, Poznan 61-614, Poland
BMC Evolutionary Biology 2014, 14:28 doi:10.1186/1471-2148-14-28Published: 17 February 2014
Geographic barriers to gene flow and divergence among populations in sexual traits are two important causes of genetic isolation which may lead to speciation. Genetic isolation may be facilitated if these two mechanisms act synergistically. The guppy from the Cumaná region (within the Cariaco drainage) of eastern Venezuela has been previously described as a case of incipient speciation driven by sexual selection, significantly differentiated in sexual colouration and body shape from the common guppy, Poecilia reticulata. The latter occurs widely in northern Venezuela, including the south-eastern side of Cordillera de la Costa, where it inhabits streams belonging to the San Juan drainage. Here, we present molecular and morphological analyses of differentiation among guppy populations in the Cariaco and San Juan drainages. Our analyses are based on a 953 bp long mtDNA fragment, a set of 15 microsatellites (519 fish from 20 populations), and four phenotypic traits.
Both microsatellite and mtDNA data showed that guppies inhabiting the two drainages are characterised by a significant genetic differentiation, but a higher proportion of the genetic variance was distributed among populations within regions. Most guppies in the Cariaco drainage had mtDNA from a distinct lineage, but we also found evidence for widespread introgression of mtDNA from the San Juan drainage into the Cariaco drainage. Phenotypically, populations in the two regions differed significantly only in the number of black crescents. Phenotypic clustering did not support existence of two distinct groupings, but indicated a degree of distinctiveness of Central Cumaná (CC) population. However, CC population showed little differentiation at the neutral markers from the proximate populations within the Cariaco drainage.
Our findings are consistent with only partial genetic isolation between the two geographic regions and indicate that the geographic barrier of Cordillera de la Costa has not played an important role in strengthening the incomplete pre-zygotic reproductive barrier between Cumaná and common guppy. Significant phenotypic differentiation between genetically similar (in terms of neutral variation) populations suggests that mate choice can maintain divergence at sexually selected traits despite gene flow. However, neither genetic nor phenotypic clustering supported delineation of two species within the region.