Variation and adaptation in the guppy, Poecilia reticulata (Dreyer, Weigel)

by admin — last modified Mar 19, 2012 02:43 PM

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A central question in ecology and evolution is how standing variation in natural populations is maintained, and how divergent natural selection shapes this variation into adaptive differences between populations and species. The Trinidadian guppy, Poecilia reticulata, represents one of the best vertebrate models for the study of how phenotypic variation within a population is linked to adaptation to specific environmental conditions. Guppies are well known for the highly polymorphic color patterns of the males that have been a subject of genetic analysis for almost a century (Winge, J. Genet. 18, 1, 1927). David Reznick and colleagues have studied these populations in the wild for many years, focusing on their ecogeographic adaptations to different river habitats. Upper and lower river populations in several drainages in Northern Trinidad are separated by barrier waterfalls and have developed different adaptive traits that are known to depend on the presence or absence of predators, among other environmental factors. Distinguishing traits include courtship and mating behavior, conspicuous color patterns of males, age and size at maturity, brood intervals and brood size.

The vast literature on its ecology and evolution and the extensive phenotypic variation in wild populations make the guppy a particularly attractive choice for understanding the molecular basis for adaptation to varying natural conditions. The long-term goal of this project, which has been jointly initiated by the Dreyer and Weigel groups with considerable help from collaborators Reznick and Breden, is to uncover the genes underlying the phenotypic variation that is the raw material for selection.

Crosses between wild-collected guppies from geographically distant locations in Trinidad and Venezuela showed that the majority of hybrids could produce viable and fertile F2 offspring, despite some indications for incipient reproductive isolation. A genetic linkage map comprising more than 700 markers on 23 linkage groups (corresponding to the known haploid chromosome number) has been constructed, based on single nucleotide polymorphisms (SNPs). The same markers have also been used to genotype a collection of different wild guppy strains from Trinidad and Venezuela for population genetic studies. Using next generation Illumina DNA sequencing, we develop additional genomic resources, namely RAD markers and a reference transcriptome and have started on a whole genome sequencing project .

A major challenge remains the fine mapping mapping of QTL that control male ornaments and body shape, and functional analysis of the color trait loci found in the gonosomal region of the Y chromosome, and their relationship to the the sex-determining locus itself. In addition, candidate genes for color pattern formation in male guppies are being examined. In collaboration with Felix Breden, we have investigated opsin photopigments and found polymorphisms in long wavelength opsins, indicative of positive selection on red and orange color perception.