Subterranean Fishes of the World

3073

2015

AIM 2015

Populations of blind and depigmented cavefish belonging to the Mexican tetra species Astyanax mexicanus are outstanding models to study the tempo and mode of adaptation to cave environment because the phenotypic convergence of these independent populations allows us to examine whether the evolution of similar phenotypes involved the fixation of standing genetic variation and/or de novo mutations. However, we do not have yet accurate estimations of the time frames of evolution of these populations that are so important for such studies. We developed a cheap, convenient and robust method to detect a recently isolated small population and estimate its age. Our approach is based on the fact that there is a transient acceleration of the neutral substitution rate in such a population. We applied this method to estimate the age of Pachón cave population which is considered the “oldest” and most isolated cavefish population. Despite recurrent claims that the isolation of this population is ancient, within the range of the late Miocene to the middle Pleistocene, we obtained evidence that it has been isolated during less than 30,000 years, that is during the Late Pleistocene. This new time frame together with other recent evidence indicate that the many phenotypic changes observed in these cavefish mainly involved the fixation of cryptic genetic variants present in surface fish populations and within a short period of time.

1