Data from: Repeated divergence in opsin gene expression mirrors photic habitat changes in rapidly evolving crater lake cichlid fishes

Abstract

Selection pressures differ along environmental gradients and organisms’ phenotypes. Traits tightly linked to fitness (e.g., the visual system) are expected to closely track environmental variation along gradients. Within such gradients, adaptation to local conditions might be due to heritable and non-heritable, environmentally induced variation. Disentangling these sources of phenotypic variation requires studying, in nature and the laboratory, closely related populations experiencing different environments. The Nicaraguan great and crater lakes show an environmental gradient in photic conditions extending from clear crater lakes to very turbid great lakes. From two old, turbid great lakes, Midas cichlid fish (Amphilophus cf. citrinellus) independently colonized seven isolated crater lakes of varying light conditions, resulting in a small adaptive radiation. We estimated the variation in visual sensitivities along this photic gradient by measuring differential cone opsin gene expression among populations from different lakes. The visual sensitivities observed in all seven derived crater lake populations have not changed randomly but shifted predictably in direction and magnitude, repeatedly mirroring changes in photic conditions. Intrapopulation phenotypic variation decreases as environments become spectrally narrower suggesting different selective landscapes within the gradient. Comparing wild-caught and lab-reared fish revealed that 48% of this phenotypic variation is genetically determined and evolved rapidly. Our results demonstrate deterministic, rapid phenotypic evolution that fine-tunes visual sensitivity to fine-scale environmental variation.