Subterranean Fishes of the World

3214

2013

AIM 2013

The surface-dwelling ancestors of cavefish adapted to dark cave environments by shifting multiple morphological and behavioral traits. Vibration attraction behavior (VAB), which is the ability of fish to swim toward the source of a water disturbance in darkness, is common in cavefish but rarely observed in surface fish. VAB is heritable, has an advantage for feeding in the dark, and is mediated by superficial neuromasts (SN), which are increased in size and number in cavefish. Mating experiments between surface fish and Pachón cavefish indicated that the enhancement of VAB and SN is paternally inherited and that SN specifically located within the cavefish eye orbit (EO) are genetically correlated with eye reduction. Ablation of EO SN in cavefish demonstrated a major role for these sensory receptors in VAB expression. The quantitative trait loci (QTL) for VAB, EO SN, and reduced eye size form two congruent or overlapping clusters on Astyanax linkage groups (LG) 2 and 17. However, despite the known involvement of the Shh signaling pathway in eye degeneration, no QTL responsible for any of these traits were found at the shh locus on LG 13. Furthermore, experimental induction of eye regression in surface fish via shh overexpression indicated that the absence of eyes is insufficient to promote the appearance of VAB or EO SN. We conclude that natural selection for VAB and EO SN enhancement may indirectly promote eye regression in Pachón cavefish through genetic linkage or antagonistic pleiotropy among the genetic factors underlying these traits. We also report the narrowed genomic intervals for VAB and EO SN genes through sequenced restriction site associated DNA tags (RAD-tags), a next generation sequencing (Illumina)-based genotyping method. We are currently identifying the genes responsible for the evolution of VAB and EO SN with the help of this method. We further show by mathematical simulation that paternal inheritance of VAB and SN can lead to the evolutionary disparity between the nuclear and mitochondrial genomes previously observed in Pachón cavefish. The results show how studies of an adaptive behavior and its sensory receptors can provide insights into cavefish evolution as well as how interdisciplinary approaches can lead to new insights into the mechanisms of the constructive evolution.

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