The molecular basis of color vision in colorful fish: four long wave-sensitive (LWS) opsins in guppies (Poecilia reticulata) are defined by amino acid substitutions at key functional sites.
BACKGROUND
Comparisons of functionally important changes at the molecular level in model systems have identified key adaptations driving isolation and speciation. In cichlids, for example, long wavelength-sensitive (LWS) opsins appear to play a role in mate choice and male color variation within and among species. To test the hypothesis that the evolution of elaborate coloration in male guppies (Poecilia reticulata) is also associated with opsin gene diversity, we sequenced long wavelength-sensitive (LWS) opsin genes in six species of the family Poeciliidae.


RESULTS
Sequences of four LWS opsin genes were amplified from the guppy genome and from mRNA isolated from adult guppy eyes. Variation in expression was quantified using qPCR. Three of the four genes encode opsins predicted to be most sensitive to different wavelengths of light because they vary at key amino acid positions. This family of LWS opsin genes was produced by a diversity of duplication events. One, an intronless gene, was produced prior to the divergence of families Fundulidae and Poeciliidae. Between-gene PCR and DNA sequencing show that two of the guppy LWS opsins are linked in an inverted orientation. This inverted tandem duplication event occurred near the base of the poeciliid tree in the common ancestor of Poecilia and Xiphophorus. The fourth sequence has been uncovered only in the genus Poecilia. In the guppies surveyed here, this sequence is a hybrid, with the 5' end most similar to one of the tandem duplicates and the 3' end identical to the other.


CONCLUSIONS
Enhanced wavelength discrimination, a possible consequence of opsin gene duplication and divergence, might have been an evolutionary prerequisite for color-based sexual selection and have led to the extraordinary coloration now observed in male guppies and in many other poeciliids.
Ward
Matthew N
MN
University of Victoria, Department of Biology, Victoria, British Columbia, Canada. rugbyman7@hotmail.com
Churcher
Allison M
AM
Dick
Kevin J
KJ
Laver
Chris R J
CR
Owens
Greg L
GL
Polack
Megan D
MD
Ward
Pam R
PR
Breden
Felix
F
Taylor
John S
JS
D019943:Amino Acid Substitution; D000818:Animals; D003118:Color Perception / Q000502:physiology*; D003532:Cyprinodontiformes / Q000235:genetics; D020440:Gene Duplication; D009030:Mosaicism; D009693:Nucleic Acid Hybridization; D010802:Phylogeny; D011036:Poecilia / Q000145:classification / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017299:Rod Opsins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology
D017299:Rod Opsins