Martineau, B. | Search bioRxiv

bioRxiv2022

Genetic mapping of craniofacial traits in the Mexican tetra reveals loci associated with bite differences between cave and surface fish

The Mexican tetra, Astyanax mexicanus, includes interfertile surface-dwelling and cave-dwelling morphs, enabling powerful studies aimed at uncovering genes involved in the evolution of cave-associated traits. Compared to surface fish, cavefish harbor several extreme traits within their skull, such as a protruding lower jaw, a wider gape, and an increase in tooth number. These features are highly variable between individual cavefish and even across different cavefish populations. To investigate these traits, we created a novel feeding behavior assay wherein bite impressions could be obtained. We determined that fish with an underbite leave larger bite impressions with an increase in the number of tooth marks. Capitalizing on the ability to produce hybrids from surface and cavefish crosses, we investigated genes underlying these segregating orofacial traits by performing Quantitative Trait Loci (QTL) analysis with F2 hybrids. We discovered significant QTL for bite (underbite vs. overbite) that mapped to a single region of the Astyanax genome. This work highlights cavefish as a valuable genetic model for orofacial patterning and will provide insight into the genetic regulators of jaw and tooth development.

evolutionary biology↗

bioRxiv2017

Insulin resistance in cavefish as an adaptation to a nutrient-limited environment

Periodic food shortage is one of the biggest challenges organisms face in natural habitats. How animals cope with nutrient limited conditions is an active area of study, of particular relevance in the context of the current increasing destabilization of global climate. Caves represent an extreme setting where animals have adapted to nutrient-limited conditions, as most cave environments lack a primary energy source. Here we show that cave-adapted populations of the Mexican Tetra, Astyanax mexicanus, have dysregulated blood glucose homeostasis and are insulin resistant compared to the river-adapted population. We found that multiple cave populations carry a mutation in the insulin receptor that leads to decreased insulin binding in vitro. Surface/cave hybrid fish carrying the allele weigh more than non-carriers, and zebrafish genetically engineered to carry the mutation similarly have increased body weight and insulin resistance. Higher bodyweight may be advantageous in the cave as a strategy to cope with infrequent food. In humans, the identical mutation in the insulin receptor leads to a severe form of insulin resistance and dramatically reduced life-span. However, cavefish have a similar lifespan to surface fish (of greater than fourteen years) and do not accumulate advanced glycated end products (AGEs) in the blood that are typically associated with progression of diabetes-associated pathologies. Our findings raise the intriguing hypothesis that cavefish have acquired compensatory mechanisms that allow them to circumvent the typical negative effects associated with failure to regulate blood glucose.

evolutionary biology↗