Morphogenesis and motility of the Astyanax mexicanus gastrointestinal tract

Abstract

Through the course of evolution, the gastrointestinal (GI) tract has been modified to maximize nutrientabsorption, forming specialized segments that are morphologically and functionally distinct. Here we show thatthe GI tract of the Mexican tetra,Astyanax mexicanus,has distinct regions, exhibiting differences inmorphology, motility, and absorption. We found thatA. mexicanuspopulations adapted for life in subterraneancaves exhibit differences in the GI segments compared to those adapted to surface rivers. Cave-adaptedfishexhibit bi-directional churning motility in the stomach region that is largely absent in river-adaptedfish. Weinvestigated how this motility pattern influences intestinal transit of powdered food and live prey. We found thatpowdered food is more readily emptied from the cavefish GI tract. In contrast, the transit of live rotifers fromthe stomach region to the midgut occurs more slowly in cavefish compared to surfacefish, consistent with thepresence of churning motility. Differences in intestinal motility and transit likely reflect adaptation to uniquefood sources available to post-larvalA. mexicanusin the cave and river environments. We found that cavefishgrow more quickly than surfacefish when fedad libitum,suggesting that altered GI function may aid in nutrientconsumption or absorption. We did not observe differences in enteric neuron density or smooth muscleorganization between cavefish and surfacefish. Altered intestinal motility in cavefish could instead be due tochanges in the activity or patterning of the enteric nervous system. Exploring this avenue will lead to a betterunderstanding of how the GI tract evolves to maximize energy assimilation from novel food sources.