Subterranean Fishes of the World

5639

2022

AIM 2022

43

Evolutionary pressures have resulted in a wide variety of anatomical changes to the brain, with development of the brain becoming tuned to the environment an animal lives in. While comparative studies show that the brain and brain regions vary anatomically across taxa, the generalized principles explaining how the brain changes are not well understood. The blind Mexican cavefish has emerged as a leading model in the study of trait evolution and offers a unique genetic model of neurological innovation to determine how the brain is shaped over evolutionary time. To determine how the brain anatomically changes while adapting to an extreme environment, we devised a brain atlas of every known neuroanatomical region that allows us to compare the variation in volume and shape of brain regions across both wildtype and hybrid populations. Functional assessment of evolutionary changes in hybrid fish reveal that neuroanatomical regions co-evolve in modules; clusters of adjacent regions in the dorsal region co-evolve together, with a concomitant change of ventral regions. This spatial relationship suggests that allelic variants of early developmental patterning genes are the primary driving forces, leading to brain-wide remodeling. Conversely, we also find that the pallium is evolving independently from those other brain regions, similar to the independent expansion of the cortex seen in primates. Therefore, we find that two models of brain evolution are occurring in the same organism, with global changes being driven by developmental constraints or tradeoffs and isolated anatomical innovations for living in a cave environment. This study is a unique example of revealing multiple models of brain anatomy evolution occurring in a single species, while also providing a genetic model for determining the cellular to brain-wide functional mechanisms driving brain evolution.

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