Visual sensitivities tuned by heterochronic shifts in opsin gene expression

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Title: Visual sensitivities tuned by heterochronic shifts in opsin gene expression
Author: Carleton, Karen L. ; Spady, Tyrone C. ; Streelman, J. Todd ; Kidd, Michael R. ; McFarland, William N. ; Loew, Ellis R.
Abstract: Background: Cichlid fishes have radiated into hundreds of species in the Great Lakes of Africa. Brightly colored males display on leks and vie to be chosen by females as mates. Strong discrimination by females causes differential male mating success, rapid evolution of male color patterns and, possibly, speciation. In addition to differences in color pattern, Lake Malawi cichlids also show some of the largest known shifts in visual sensitivity among closely related species. These shifts result from modulated expression of seven cone opsin genes. However, the mechanisms for this modulated expression are unknown. Results: In this work, we ask whether these differences might result from changes in developmental patterning of cone opsin genes. To test this, we compared the developmental pattern of cone opsin gene expression of the Nile tilapia, Oreochromis niloticus, with that of several cichlid species from Lake Malawi. In tilapia, quantitative polymerase chain reaction showed that opsin gene expression changes dynamically from a larval gene set through a juvenile set to a final adult set. In contrast, Lake Malawi species showed one of two developmental patterns. In some species, the expressed gene set changes slowly, either retaining the larval pattern or progressing only from larval to juvenile gene sets (neoteny). In the other species, the same genes are expressed in both larvae and adults but correspond to the tilapia adult genes (direct development). Conclusion: Differences in visual sensitivities among species of Lake Malawi cichlids arise through heterochronic shifts relative to the ontogenetic pattern of the tilapia outgroup. Heterochrony has previously been shown to be a powerful mechanism for change in morphological evolution. We found that altering developmental expression patterns is also an important mechanism for altering sensory systems. These resulting sensory shifts will have major impacts on visual communication and could help drive cichlid speciation.
Description: © 2008 Carleton et al; licensee BioMed Central Ltd. The electronic version of this article is the complete one and can be found online at: DOI:10.1186/1741-7007-6-22
Type: Article
ISSN: 1741-7007
Citation: Carleton, K.L., T.C. Spady, J.T. Streelman, M.C. Kidd, W.N. McFarland and E.R. Loew, "Visual sensitivities tuned by heterochronic shifts in opsin gene expression," BMC Biology 6: 22.
Date: 2008-05-23
Contributor: Georgia Institute of Technology. School of Biology
University of Maryland (College Park, Md.). Dept. of Biology
National Human Genome Research Institute (U.S.)
University of Texas at Austin. Section of Integrative Biology
Friday Harbor Laboratories (Wash.)
Cornell University. Dept. of Biomedical Sciences
Publisher: Georgia Institute of Technology
BioMed Central
Subject: Cichlids
Opsin gene expression
Visual sensitivity

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