Sensing in the dark: constructive evolution of the lateral line system in blind populations of Astyanax mexicanus

Cave adapted animals evolve a suite of regressive and constructive traits that allow survival in the dark. Most studies aiming at understanding cave animal evolution have focused on the genetics and environmental underpinnings of regressive traits, with special emphasis on vision loss. However, cave-associated constructive traits, like compensations from non-visual sensory systems, have been relatively overlooked. In blind cavefish of the Mexican tetra, Astyanax mexicanus, a major non-visual sensory system that compensated through morphological expansions is the mechanosensory lateral line. Although this system has been studied and described in A. mexicanus for over decades, there are still many unknowns about the developmental origin, synaptic plasticity, and overall adaptive value of expanded lateral lines. This review provides a snapshot of the current state of knowledge of lateral line adaption in A. mexicanus, with an emphasis on anatomy, synaptic plasticity, and behavior. Multiple open avenues for future research in this system, and how these can be leveraged as tools for both evolutionary biology and evolutionary medicine, are discussed.