Subterranean Fishes of the World

3255

2017

AIM 2017

Animals that thrive in low-nutrient environments evolved to efficiently consume and utilize energy in ways that are not fully understood. Cave forms of Astyanax mexicanus survive long periods of starvation, weigh more than surface counterparts on the same diet, and have a higher fat content. We aim to identify quantitative trait loci (QTL) for these characteristics by genotyping and phenotyping 225 individually-housed F2 Surface/Tinaja hybrids fed precisely the same diet. Surface and Tinaja cavefish have quantitative differences in the GI tract; Tinaja cavefish have a significantly longer GI tract and fewer, but larger, digestive appendages called pyloric caeca. These features likely alter metabolism by increasing digestive surface area and thus capacity for nutrient absorption. Interestingly, intestine length in the F2 population correlates with fat content. Also in line with evidence for greater nutrient absorption, Tinaja appear to accumulate foodderived carotenoids in their visceral fat. Carotenoids are yellow vitamin A precursors important for vision and pigmentation. Yellow fat is however independent of eyes or melanin production; Molino cavefish and some eyeless F2 Surface/Tinaja hybrids have white fat, and vice versa some F2 hybrids with eyes have yellow fat, leading us to hypothesize that yellow fat is due to increased capacity for carotenoid absorption. In addition to GI morphology, the relative proportion of intestinal cell types and their proliferation dictates the function and energetic cost of the GI tract. We are using a combination of histology and flow cytometry to quantify cellular-level differences in the GI tract of our F2 population with the goal of uncovering the genetic control of intestinal cell-type maintenance and its role in metabolism. Taken together our results will lead to a better understanding of physiological adaptation in a low nutrient environment.

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