Meeting Abstract
Animals flourish in nearly every environment on Earth as they have evolved numerous mechanisms to efficiently assimilate and use energy. How the GI tract evolves in response to change is not well understood although dramatic variation in structure and function is apparent across species. We are investigating GI evolution in a single species in the process of diversifying: the teleost fish Astyanax mexicanus. This fish exists as a river-dwelling form with abundant food, and multiple independently derived cave-dwelling forms that are entirely reliant on external food sources brought in by flooding. Although separated for millions of years, the river and all cave forms are interfertile allowing us to investigate the genetic basis of evolution in a low-nutrient environment. Cavefish have increased appetite and fat storage, and can survive long periods of starvation. We examined the GI tract of fish from the river and the Tinaja cave and found that cavefish have a longer and wider GI tract that, unlike the GI tract of the river fish, does not shrink dramatically during starvation. These differences may represent altered intestinal stem cell dynamics. The cavefish GI tract is also morphologically distinct; Tinaja have 6 finger-like projections posterior to the stomach (pyloric caeca), while river have 7 to 10 caeca. These mysterious structures vary from 1 to 1,000 in fish species. Caeca number is a multigenic trait; only 3 individuals in a population of 98 F2 River/Tinaja hybrids have 6 caeca. We have quantified fat content, activity, blood glucose, weight loss, and relative gut length in F2 hybrids and are currently using RADseq to identify quantitative trait loci. Our aim is to understand the genetic changes that underlie evolution of metabolism and GI morphology in a low nutrient environment.
