Evolution of gastrointestinal tract morphology and plasticity in cave-adapted Mexican tetra, Astyanax mexicanus

Abstract

The gastrointestinal tract has evolved in numerous ways to allow animals to optimally assimilate energy from different food sources. The morphology and physiology of the gut is plastic and can be greatly altered by diet in some animals. In this study, we investigate the evolution and plasticity of gastrointestinal tract morphology by comparing laboratory raised cave-adapted and river-adapted forms of the Mexican tetra, Astyanax mexicanus reared under different dietary conditions. In the wild, river-dwelling populations (surface fish) consume plants and insects throughout the year, while cavedwelling populations (cavefish) live in a perpetually-dark environment dependent on nutrient-poor food brought in by bats or seasonal floods. We find that multiple cave populations converged on a reduced number of digestive appendages called pyloric caeca and that some cave populations have a lengthened gut while others have a shortened gut.Moreover, we identified differences in how gut morphology and proliferation of the epithelium respond to diet between surface fish and cavefish. Using a combination of quantitative genetic mapping, population genetics, and RNA sequencing we implicate molecular and genetic changes influencing cell proliferation, cell signaling, and immune system function in the evolution of gut morphology.

Comparative transcriptomics reveal tissue level specialization towards diet in prickleback fishes

“…This indicates changes on the molecular level to achieve a larger gut (Castoe et al 2011 ). The changes in gut size and concomitant changes in gene expression support models of cellular hypertrophy (Starck 2005 ; Leigh et al 2018 ) or cellular proliferation (Riddle et al 2020 ) in fishes, that can affect gut surface area (e.g., Leigh et al 2018 ).…”

“…We confirmed that gut length varies with diet quality, even intra-specifically, but there are limits to this since the herbivorous X. mucosus H always had a longer gut than the other species, even when they consumed the same diet in the laboratory. Thus, gut length definitely has a genetic underpinning and is not just plastic (German and Horn 2006 ; Sullam et al 2015 ; Riddle et al 2020 ). We observed positive selection on, and increased expression of, genes that would contribute to increased epithelial surface area in X. mucosus H , but not the other taxa.…”

Patterns of Differentially Expressed circRNAs in Human Thymocytes

“…At the same time, it assembles and quantifies expression levels for transcriptome features in a readable Ballgown-like format (via the -B option). Expression pattern analysis makes it possible to identify and extract cohorts of genes that behave in a coordinated manner with respect to the complete set of genes and associate it with a particular biological context [31][32][33][34]. This type of analysis provides evidence of possible gene and/or functional interactions between genes co-expressed under different conditions or over time.…”