MBE Advance Access published online on July 3, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm132
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© 2007 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Research Article |
Gene duplication is an evolutionary mechanism for expanding spectral diversity in the long wavelength photopigments of butterflies
1 Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697
2 Department of Electrical Engineering, University of Washington, Seattle, WA 98195
3 Department of Biology, Middle Tennessee State University, Murfreesboro, TN 37132
* Address for correspondence: abriscoe{at}uci.edu, University of California, Irvine, Department of Ecology and Evolutionary Biology, 321 Steinhaus Hall, Irvine, CA 92697 U.S.A., Tel. (949) 824-1118, Fax. (949) 824-2181
Received for publication April 29, 2007. Revision received June 15, 2007. Revision received June 20, 2007. Accepted for publication June 22, 2007.
Butterfly long wavelength (L) photopigments are interesting for comparative studies of adaptive evolution because of the tremendous phenotypic variation that exists in their wavelength of peak absorbance (
max value). Here we present a comprehensive survey of L photopigment variation by measuring max in 12 nymphalid and 1 riodinid species using epi-microspectrophotometry. Together with previous data, we find that L photopigment max varies from 510-565 nm in 22 nymphalids, with an even broader 505-600 nm range in riodinids. We then surveyed the L opsin genes for which max values are available as well as from related taxa and found two instances of L opsin gene duplication within nymphalids, in Hermeuptychia hermes and Amathusia phidippus, and one instance within riodinids, in the metalmark butterfly, Apodemia mormo. Using maximum parsimony and maximum likelihood ancestral state reconstructions to map the evolution of spectral shifts within the L photopigments of nymphalids, we estimate the ancestral pigment had a max=540 nm±S.E.10 nm and that blue-shifts in wavelength have occurred at least 4 times within the family. We used ancestral state reconstructions to investigate the importance of several amino acid substitutions (Ile17Met, Ala64Ser, Asn70Ser and Ser137Ala) previously shown to have evolved under positive selection that are correlated with blue spectral shifts. These reconstructions suggest that the Ala64Ser substitution has indeed occurred along the newly identified blue-shifted L photopigment lineages. Substitutions at the other three sites may also be involved in the functional diversification of L photopigments. Our data strongly suggest that there are limits to the evolution of L photopigment spectral shifts among species with only one L opsin gene and that opsin gene duplication broadens the potential range of max values.
Key Words: visual pigment • gene duplication • Nymphalidae • Riodinidae • opsin • color vision
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