Subterranean Fishes of the World

5611

2022

AIM 2022

18

Extreme environments can have profound impacts on the evolution of sensory traits. Cave systems frequently involve the complete or near absence of light, which is associated with the regression or expansion of different senses. Expanded senses likely assist in aiding survival, particularly to compensate for the loss of vision. Taste, for instance, is crucial for detecting and differentiating beneficial food items from those that pose a risk to organismal health. The Mexican tetra, Astyanax mexicanus, is ideal for investigating the genetics and development of sensory expansions owing to its two drastically different morphotypes that have evolved unusual adaptations to their respective environments. For decades we have known that the cave morphotype has a radically increased number of external taste buds (TBs) compared to their surface counterpart, however the timing of this external expansion and the genetic architecture has not been comprehensively interrogated. We used immunofluorescent histochemistry to examine the timing (and differences) in dorsal and ventral spatial expansion of external taste buds between the surface morphotype and two distinct cave populations of A. mexicanus. Calretinin-positive staining revealed that the distance of the expansion reaches significance around six- and nine-months post-fertilization. Quantitative trait loci analyses performed on a surface x Pachón F2 pedigree linked numerous external gustatory-related phenotypes to two main genetic regions. Interestingly, these regions seem to be associated with different spatial regions of expansion, with chromosome 7 being linked to dorsal and lateral expansions and chromosome 15 associated with the ventral expansion of taste buds, consistent with work performed in other systems. Together, this work sheds light on both the developmental timing and genetic architecture of extraoral taste, an important example of constructive evolution.

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