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Sleep is an evolutionarily ancient behavior, yet multiple cave-dwelling populations of the Mexican tetra, Astyanax mexicanus, have converged on sleep loss compared to surface fish. However, most of the 34 cave populations remain unstudied, and sleep in natural habitats is largely unknown. To address this, we measured sleep and activity in 15 representative populations of surface, cave, and hybrid populations. All cavefish and hybrid populations tested exhibited drastically reduced sleep, including hybrid populations with diverse eye and pigmentation phenotypes. Mapping behavior onto the A. mexicanus phylogeny revealed that reduced sleep and elevated locomotor activity evolved independently multiple times. Field experiments confirmed that wild fish also exhibit sleep loss, paralleling laboratory findings. These results demonstrate deep evolutionary convergence on sleep loss across cavefish lineages and suggest that sleep reduction is a primary trait contributing to adaptation in subterranean environments. 

Population divergence is often quantified using phenotypic variation. However, because sensory abilities are more difficult to discern, we have little information on the plasticity and rate of sensory change between different environments. The Mexican tetra (Astyanax mexicanus) is a fish distributed throughout Southern Texas and Northern Mexico and has evolved troglomorphic phenotypes, such as vestigial eyes and reduced pigmentation, when surface ancestors invaded caves in the past several hundred thousand years. In the early 1900s, surfaceA. mexicanuswere introduced to the karstic Edwards-Trinity Aquifer in Texas. Subsequent cave colonization of subterranean environments resulted in fish with phenotypic and behavioral divergence from their surface counterparts, allowing examination of how new environments lead to sensory changes. We hypothesized that recently introduced cave populations would be more sensitive to light and sound when compared to their surface counterparts. We quantified divergence using auditory evoked potentials (AEPs) and particle acceleration levels (PALs) to measure differences in sound sensitivity, and electroretinography (ERGs) to measure light sensitivity. We also compared these results to measurements taken from native populations and lab-born individuals of the introduced populations. Honey Creek Cave fish were significantly more sensitive than proximate Honey Creek surface fish to sound pressure levels between 0.6 and 0.8 kHz and particle acceleration levels between 0.4 and 0.8 kHz. Pairwise differences were found between San Antonio Zoo surface and the facultative subterranean San Pedro Springs and Blue Hole populations, which exhibited more sensitivity to particle acceleration levels between 0.5 and 0.7 kHz. Electroretinography results indicate no significant differences between populations, although Honey Creek Cave fish may be trending toward reduced visual sensitivity. Auditory thresholds between wild-caught and lab-raised populations of recently invaded fish show significant differences in sensitivity, suggesting that these traits are plastic. Collectively, while these results may point to the rapid divergence ofA. mexicanusin cave habitats, it also highlights the responsive plasticity ofA. mexicanusauditory system to disparate environments.