In the Light of Evolution Volume I: Adaptation and Complex Design (2007) / Chapter Skim
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Pages 187-204
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From page 187... ...
BrisCoe* Butterflies and primates are interesting for comparative color vision studies, because both have evolved middle- (M)
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From page 188... ...
Because photopigment sensitivities represent clear adaptations to an animal's light environment (yokoyama, 1997) , the amino acid sites of opsins involved in spectral tuning may be under positive selection, which has been most extensively studied in fish, mammals, and primates (surridge et al., 2003; spady et al., 2005; yokoyama and Takenaka, 2005)
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From page 189... ...
natural selection has recruited both the vertebrate ciliary opsins and the insect rhabdomeric opsins for use in achromatic and color vision. Moreover, mammals use all their cone photopigments for color vision, and although not yet fully investigated, butterflies likely use all their major spectral receptor types for color vision (Kelber and henique, 1999; Kelber, 2001; Kelber et al., 2003)
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From page 190... ...
our combined approaches suggest that similar amino acid sites are indeed involved in the evolution of color vision in both primates and butterflies.
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From page 191... ...
ABSORBANCE SPECTRA AND OPSIN SEQUENCES OF LImEnItIs L PHOTOPIGMENTS To test for evidence of positive selection of spectral tuning sites in nymphalid l photopigments, we first searched for l photopigments whose λmax values varied among closely related species. The λmax values of l photopigments from a number of nymphalid species were evaluated by using epimicrospectrophotometry, a method (Bernard, 1983)
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From page 192... ...
and Limenitis archippus floridensis, to 530 nm in Limenitis lorquini and Limenitis weidemeyerii, to 545 nm in Limenitis arthemis astyanax (Fig.
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To evaluate candidate spectral tuning sites, we next determined the opsin gene sequences that correspond to the encoded l photopigment spectral phenotypes. We thus cloned the full-length l opsin cDnA from L
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From page 194... ...
test, character mapping, parallel/convergent change analysis, and branch-site test of selection, to define specific spectral tuning sites that may be under positive selection. MK Test for Selection Differences in the amino acid sequences of proteins among species may be due to the accumulation of neutral mutations by drift, the fixation of adaptive mutations by positive selection, or a combination of the two.
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From page 195... ...
arthemis astyanax l opsin genes have evolved under positive selection for divergent functions. This allowed us to focus on specific sites within the encoded protein that are under positive selection and involved in spectral tuning.
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From page 196... ...
TABle 10.1 Allelic variation in 597 bp of Coding region of l opsin Gene in 24 L arthemis astyanax individuals (48 Chromosomes)
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Thick black lines indicate nymphalid branches along which blue spectral shifts occurred that were investigated in the parallel/convergent change and branch-site tests of selection. extant blue-shifted sequences are underlined.
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From page 198... ...
coenia opsin, two further parallel amino acid changes were observed associated with parallel blue spectral shifts: an alanine-to-serine substitution at amino acid residue 64 and an asparagine-to-serine substitution at amino acid residue 70. Branch-Site Models of Selection Although parallel/convergent change analysis depends on reconstruction of amino acid sequences, a much stronger positive selection inference can be made by using reconstruction of nucleotide sequences.
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From page 199... ...
. This result is provocative, because previous attempts to identify amino acid sites under positive selection in both butterfly and vertebrate photopigments by using similar methods have largely failed despite robust physiological data (i.e., absorbance spectra)
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The amino acid residues are numbered relative to their alignment position. Arrows, amino acid sites under positive selection.
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arthemis astyanax (which can hybridize in nature) , show a commonly observed primate polymorphism.
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arthemis astyanax and one L archippus archippus individuals genotyped, leaving 597 bp of coding region that was aligned.
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From page 203... ...
For the parallel change analysis, amino acid substitutions along each lineage in the opsin gene tree were reconstructed by using maximum parsimony in MacClade (Maddison and Maddison, 2005) and maximum likelihood in PAMl (yang, 1997)
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From page 204... ...
(Guex and Peitsch, 1997) , and candidate spectral tuning sites were mapped onto the 3D homology model.
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