Divergent selection on opsins drives incipient speciation in Lake Victoria cichlids.

Shinji Mizoiri,Kazuhiko Takahashi,Tetsu Sato,Masakatsu Watanabe,Tohru Sugawara,Yohey Terai,Nellie Konijnendijk,Takeshi Sasaki,Hillary D J Mrosso,Hiroo Imai,Norihiro Okada,Hidenori Tachida,Yoshinori Shichida,Ole Seehausen

doi:10.1371/journal.pbio.0040433

Abstract

Divergent natural selection acting on ecological traits, which also affect mate choice, is a key element of ecological speciation theory, but has not previously been demonstrated at the molecular gene level to our knowledge. Here we demonstrate parallel evolution in two cichlid genera under strong divergent selection in a gene that affects both. Strong divergent natural selection fixed opsin proteins with different predicted light absorbance properties at opposite ends of an environmental gradient. By expressing them and measuring absorbance, we show that the reciprocal fixation adapts populations to divergent light environments. The divergent evolution of the visual system coincides with divergence in male breeding coloration, consistent with incipient ecological by-product speciation.

Highlights

Adaptive radiation, the generation of ecological diversity in a rapidly multiplying lineage, is receiving much attention by evolutionary biologists and ecologists because it is thought to be a force able to quickly generate large numbers of new species and ecological diversity through multiple episodes of ecological speciation [1]
We report the results on N. greenwoodi/omnicaeruleus first and compare results on the three other species against them
Persistence of L/H allele polymorphisms seems rare in contemporaneous populations, and we found no evidence for L/M3 polymorphisms at all (Figures 1 and S6)

Summary

Incipient Speciation in Lake Victoria Cichlids

Divergent natural selection acting on ecological traits, which affect mate choice, is a key element of ecological speciation theory, but has not previously been demonstrated at the molecular gene level to our knowledge. We demonstrate parallel evolution in two cichlid genera under strong divergent selection in a gene that affects both. Strong divergent natural selection fixed opsin proteins with different predicted light absorbance properties at opposite ends of an environmental gradient. By expressing them and measuring absorbance, we show that the reciprocal fixation adapts populations to divergent light environments. The divergent evolution of the visual system coincides with divergence in male breeding coloration, consistent with incipient ecological by-product speciation

Introduction

Materials and Methods

Supporting Information