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). 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
- Group leader
- Dr. Stefan Henz
- Staff scientist in bioinformatics
- Dr. Margarete Hoffmann
- Postdoctoral fellow
- Namita Tripathi
- Ph.D. 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. Nicolas Langdale
- Laboratoire des Interactions Plantes Micro-organismes, Castanet Tolosan, France
- Dr. David Reznick
- UC Riverside, California, US
Key publications
- 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), in press.
Positions open
We offer a Ph. D. project on
Transcriptome analysis of the guppy and detecting genes controlling male sex and male ornaments
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. The sex determining locus (SDL) on the Y chromosome is linked to several ornamental genes.
Functional dissection of the guppy SDL and its relationship to the strictly Y-linked ornamental genes will provide further insight in the evolution of sex chromosomes and in the molecular evolution of sex determining genes. This project will involve the use of advanced methods such as high-throughput genotyping, comparative transcriptome analysis as well as whole-genome analyses by next-generation DNA sequencing (Illumina).
Applicants should be trained in molecular genetics and be interested in mechanisms of sex determination and evolution of sex chromosomes. This project is 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 christine.dreyer at tuebingen.mpg.de
The Max Planck Society is an equal opportunity employer and is committed to improving opportunities for women in science.
The following project on
Male Nuptial Ornaments of the guppy
would be suitable for a
- Diploma or Ph. D. Student with interest in Developmental Biology and molecular genetics.
The pathways of specification, migration, clonal expansion and positioning of the various pigment cell types shaping the male nuptial pattern of guppies after puberty 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 neural crest cells in embryogenesis by means of in situ hybridization, genetic and molecular analysis of genes involved in pigmentation, and the role of hormonal signals on cell differentiation. Since we have recently constructed a genetic map of the guppy, QTL mapping will reveal further Poecilia-specific candidate genes and lead to further fine mapping of these loci.
Applications by e-mail to Christine Dreyer
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