Allelic variation in the squirrel monkey x-linked color vision gene: biogeographical and behavioral correlates |
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Authors: | Cropp Susan Boinski Sue Li Wen-Hsiung |
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Institution: | (1) Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637, USA, US;(2) Department of Anatomy & Neurobiology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA, US;(3) Department of Anthropology, 1112 Turlington Hall, P.O. Box 117305, University of Florida, Gainesville, FL 32611-7305, USA, US |
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Abstract: | Most Neotropical primate species possess a polymorphic X-linked and a monomorphic autosomal color vision gene. Consequently,
populations are composed of both dichromatics and trichromatics. Most theories on the maintenance of this genetic system revolve
around possible advantages for foraging ecology. To examine the issue from a different angle, we compared the numbers and
relative frequencies of alleles at the X-linked locus among three species of Saimiri representing a wide range of geographical and behavioral variation in the genus. Exons 3, 4, and 5 of the X-linked opsin
gene were sequenced for a large number of X chromosomes for all three species. Several synonymous mutations were detected
in exons 4 and 5 for the originally reported alleles but only a single nonsynonymous change was detected. Two alleles were
found that appeared to be the result of recombination events. The low occurrence of recombinant alleles and absence of mutations
in the amino acids critical for spectral tuning indicates that stabilizing selection acts to maintain the combinations of
critical sites specific to each allele. Allele frequencies were approximately the same for all Saimiri species, with a slight but significant difference between S. boliviensis and S. oerstedii. No apparent correlation exists between allele frequencies and behavioral or biogeographical differences between species,
casting doubt on the speculation that the spectral sensitivities of the alleles have been maintained because they are specifically
well-tuned to Saimiri visual ecology. Rather, the spectral tuning peaks might have been maintained because they are as widely spaced as possible
within the limited range of middlewave to longwave spectra useful to all primates. This arrangement creates a balance between
maximizing the distance between spectral tuning peaks (allowing the color opponency of the visual system to distinguish between
peaks) and maximizing the number of alleles within a limited range (yielding the greatest possible frequency of heterozygotes). |
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Keywords: | : Saimiri — Opsin polymorphism — Dichromacy — Trichromacy |
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