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

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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. Despite the wealth of field studies and the availability of feral as well as inbred strains, knowledge of the mechanistic foundation of these phenomena is scarce to non-existent.

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. As a first step, genomic resources have been generated. cDNA libraries have been produced from several tissues and strains and EST sequences have been assembled in a database that currently comprises 18.000 entries, representing 6000 different ESTs. Further, about 0.5% of the genome has been analyzed by end sequencing of BAC clones from a genomic library of male Cumaná guppies. 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) found in expressed genes and in genomic DNA sequenced at random (Namita Tripathi, a former graduate student). The same markers have also been used to genotype a collection of different wild guppy strains from Trinidad and Venezuela (Eva Willing).

After mapping of QTL that control male ornaments and body shape, we will aim at mapping QTL underlying the more subtle variation that shapes adaptation to different habitats in the wild.

A major challenge remains the fine mapping 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 specification, migration and differentiation of pigment cells in male guppies are being examined. In collaboration with Felix Breden, we have investigated opsin photopigments and found polymorphisms in long wavelength opsins between different individuals and populations, indicative of positive selection on red and orange color perception.

Personnel

Dr. Christine Dreyer christine.dreyer@tuebingen.mpg.de

Group leader

Dr. Stefan Henz

Staff scientist in bioinformatics

Jakob-Andreas Hodyl

Diploma student

 

Dr. Margarete Hoffmann

Postdoctoral fellow

Verena Kottler

Diploma student

Dr. Detlef Weigel

Director

Eva-Maria Willing

Ph.D. student

Collaborators

Dr. Paul Bentzen

Dalhousie University, Halifax, Canada

Dr. Felix Breden

Simon Fraser University, British Columbia, Canada

Dr. Joanne Cable

Cardiff University, Cardiff, UK

Dr. David Reznick

UC Riverside, California, US

Key publications

• Martyn M, Weigel D, Dreyer C. (2006) In vitro culture of embryos of the guppy, Poecilia reticulata. Developmental Dynamics, 235, 605-614.

• Hoffmann M, Tripathi N, Henz SR, Lindholm AK, Weigel D, Breden F, Dreyer C. (2007) Proceedings of the Royal Society B: Biological Sciences, 274, 33-42.
• Dreyer C, Hoffmann M, Lanz C, Willing EM, Riester M, Warthmann N, Sprecher A, Tripathi N, Henz SR, Weigel D. (2007) ESTs and EST-linked polymorphisms for genetic mapping and phylogenetic reconstruction in the guppy, Poecilia reticulata. BMC Genomics 8, 269.
• Tripathi N, Hoffmann M, Dreyer C.(2008) Natural Variation of Male Ornamental Traits of the Guppy, Poecilia reticulata, ZEBRAFISH, 5(4):265-278.
• Tripathi N, Hoffmann M, Willing EM, Lanz, C Weigel, D, Dreyer C. (2009) Genetic linkage map of the guppy, Poecilia reticulata, and quantitative trait loci analysis of male size and colour variation. Proc. R. Soc. B published online before print March 18, 2009, doi:10.1098/rspb.2008.1930.

Positions open

We offer a Ph. D. project on

Male Nuptial Ornaments of the Guppy

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. Ornamental colours provide an instructive example of male advantageous traits that are inherited in a sex-linked manner. We have recently established a dense genetic map of the guppy as a major step towards localizing genes involved in quantitative traits, including ornaments important for male courtship. Several ornamental genes are  linked to the sex determining locus (SDL) on the Y chromosome. Male nuptial ornaments of guppies become overtly visible after puberty. The pathways of specification, migration, clonal expansion and positioning of pigment cell progenitors shaping these patterns offer a range of fascinating questions to be elucidated. The project comprises cloning of candidate genes known to be involved in regulation of pigment patterns of other vertebrates, identification of pigment cell progenitors in embryogenesis by means of in situ hybridization, genetic and molecular analysis of genes involved in pattern formation, and the role of hormonal signals on cell differentiation. With a recently constructed genetic map of the guppy,  Poecilia specific candidate loci are identified by QTL mapping  and next-generation DNA sequencing (Illumina) will be used for fine mapping of these loci.

We offer a Ph. D. project on

Mapping of Selected Traits of the Guppy

Guppies living in contrasting river habitats with different predator regimes evolve quantitative adaptive traits from standing variation. Such traits include the quality of male ornaments, courtship behavior, and life history traits.  

The genetic and molecular basis of such adaptive traits shall be studied by QTL analysis in offspring from mapping crosses and by identifying signatures of selection in the genome.  Fine mapping of QTL will require  advanced methods such as high-throughput genotyping and next-generation genome  sequencing (Illumina).

Applicants should be trained in developmental biology, molecular genetics or bioinformatics and be interested in ecology and  evolution. These projects are jointly supervised by Detlef Weigel and Christine Dreyer, who are leading highly interactive international team working at the cutting edge of natural variation and evolution in animals and plants.

Applications should be directed by e-mail to Christine Dreyer.