Analysis of multi-trait evolution across independently evolved cavefish populations reveals shared and independent evolution of suites of cave-associated traits.

Environmental perturbations often lead to the evolution of multiple traits. Determining whether shared genetic factors underlie multi-trait evolution is a central question in evolutionary biology. In the Mexican tetra, Astyanax mexicanus, cave-dwelling populations have repeatedly evolved multiple traits. The repeated evolution of these traits, paired the robust environmental differences between the surface and cave habitats, provide an opportunity to investigate the genetic basis of multi-trait evolution. Here, we investigate the extent to which shared genetic mechanisms underlie the repeated evolution of multiple traits in cavefish. Across cave populations, we find evidence for shared and distinct genetic mechanisms contributing to the evolution of individual traits. Further, multiple traits covary in cave-surface F2 hybrids and many of the same trait correlations are found across independently evolved cave populations. Finally, we assessed traits that differ between pigmented and albino F2 fish in surface fish with mutations in the albinism gene oculocutaneous albinism 2 (oca2). This revealed that mutations in oca2 reduce bottom-dwelling behavior in A. mexicanus. Together, these findings suggest that multi-trait evolution occurs repeatedly through shared genetic factors across A. mexicanus cave populations. These results are consistent with pleiotropy or linkage playing a large role in multi-trait evolution in this species.