Subterranean Fishes of the World

4273

2019

AIM 2019

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Vertebrates display remarkable diversity of sex determining (SD) mechanisms, ranging from environmental to genetic sex determination (ESD and GSD). In teleosts, sex determination (SD) mechanisms include both environmental and genetic regulation and are extremely diverse, changeable, and labile. In addition, many sex-determining (SD) genes have been already found in this group of vertebrates, showing that SD genes can be extremely variable even between closely related species. Hence, teleost fish have emerged as interesting models to study the macroevolution of SD mechanisms within vertebrates. The cavefish Astyanax mexicanus belongs to the Characiform group. Different populations of Astyanax have been described, including pigmented river-dwelling and several depigmented blind cave populations. These populations are still inter-fertile and are amenable to genetic manipulations. Altogether, this makes surface and cave populations a particularly interesting evolutionary genetic model system for comparative and microevolution studies. We thus initiated studies on the microevolution of SD and SD genes in the cavefish Astyanax mexicanus, and used restriction site-associated DNA (RAD) sequencing and pool-sequencing approaches to identify sex-biased molecular markers in both cavefish originating from the Pachón cave and surface fish populations. Our first results led to the identification of a candidate master SD gene that potentially triggers SD in both morphs. Despite this conservation of a strict GSD and the same master SD gene in both populations, our results also reveal a fast evolutionary transition between a polygenic SD system in surface population and a simple monofactorial system in the Pachón cave population.

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