Subterranean Fishes of the World

5638

2022

AIM 2022

42

Alterations in craniofacial patterning were among the first morphological changes reported in the holotype cavefish specimen by Hubbs and Innes in 1936. We can now bring these observations into a modern context by using quantitative genetics to uncover the genes associated with the evolution of phenotypic changes driven by the extreme cave environment. Compared to surface fish, cavefish harbor several extreme traits within their skull, such as asymmetrical patterning, a protruding lower jaw (underbite), and an increase in tooth number. These features are highly variable across individual cavefish and even different cavefish populations. Capitalizing on the ability to produce large mapping pedigrees from interfertile surface and cavefish, we investigated genes underlying these segregating orofacial traits by performing Quantitative Trait Loci (QTL) analysis in F2 hybrids. We discovered significant QTL for both bite (underbite vs. overbite) and lower jaw size. Using the BLAST algorithm, we mapped our QTL, along with previously published QTL, to the Astyanax genome. The list of candidate genes was narrowed down by a search for both coding sequence and gene expression changes. Once such gene, REREa, falls within the QTL region associated with mandible length. This gene exhibits a missense mutation in the coding region and is significantly upregulated in the developing jaw at 30dpf. Interestingly, REREa interacts with members of the fibroblast growth factor (FGF) pathway, such as fgf8, which is involved in both bone and tooth development. REREa is also known to be associated with asymmetrical development during embryogenesis. Taking together, REREa may be implicated in the evolution of multiple cave-associated craniofacial phenotypes, such as cranial asymmetry, expansion of the lateral line system and the extension of the lower jaw.

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