Meeting Abstract
The colonization of extreme environments is typically accompanied by extreme morphological changes. Life in complete darkness has driven the evolution of a suite of troglobitic features in the blind Mexican cavefish (Astyanax mexicanus), such as eye and pigment loss. While regressive evolution is a hallmark of obligate cave-dwelling organisms, putatively adaptive, constructive traits commonly arise as well. Here, we combine quantitative analysis with behavioral studies to begin to characterize mechanosensory neuromast patterning and function in the cavefish cranium. Previously, we discovered that cavefish harbor numerous cranial bone asymmetries: fluctuating asymmetry of individual dermal bones and directional asymmetry in a dorso-cranial bend of the skull biased toward the left. This asymmetry is mirrored by the asymmetrical patterning of cranial neuromasts. We explored the relationship between facial bones and neuromasts using in vivo fluorescent co-labeling, micro-computed tomography, and quantitative trait loci (QTL) association studies. We found an increase in neuromast density within dermal bone boundaries across three distinct populations of cavefish compared to surface-dwelling fish. We reasoned that a bend in the dorsal region of the skull may expose more neuromasts to water flow on the opposite side of the face, thus enhancing sensory input and spatial mapping in the dark. We tested this using a behavioral assay to assess swimming direction in fish with a leftward bend in the skull compared to fish with no bend. Our results suggest that facial asymmetry may have evolved as a mechanism to enhance sensory input in the absence of light.
