Genetic identification and reiterated captures suggests that theAstyanax mexicanusEl Pachón cavefish population is closed and declining

Abstract

The size of Astyanax mexicanus blind cavefish populations of North-East Mexico is a demographic parameter of great importance for investigating a variety of ecological, evolutionary and conservation issues. However, very few estimates have been obtained. For these mobile animals living in an environment difficult to explore as a whole, methods based on capture-mark-recapture are appropriate, but the feasibility of such approach and the interpretation of the results depend on several assumptions that must be carefully examined. Here, we provide evidence that minimally invasive genetic identification from captures at different time intervals can give insights on cavefish population size dynamics as well as other important demographic parameters of interest. We also provide tools to calibrate sampling and genotyping efforts necessary to reach a given level of precision. Our results suggest that the El Pachon cave population is currently very small, of an order of magnitude of a few hundreds of individuals, and is distributed in a relatively isolated area. The probable decline in population size in the El Pachon cave since the last census in 1971 raises serious conservation issues.

The prevalence of copy number increase at multiallelic copy number variants associated with cave colonization

“…The singleton proportion as well as the CNV presence–absence pattern suggests low genetic diversity within the Pachón population (Figure 1). This population is characterized by small size and stronger isolation, and our results align with the low polymorphism observed from microsatellite data (Legendre et al., 2023).…”

“…Additionally, other factors may contribute to the observed patterns, such as the population size and the degree of migration between populations. Recent findings suggest that the Pachón population consists of only a few hundred individuals inhabiting a relatively isolated area, the direct consequences of which are low genetic polymorphism and limited gene flow from surface or other cave populations (Legendre et al., 2023). Accordingly, among the studied populations in our analyses, Pachón shows low diversity at the level of CNVs.…”

Acoustic signatures in Mexican cavefish populations inhabiting different caves

“…Sound architecture does not seem to evolve in a predictable manner according to geography or local biotic and abiotic conditions, and may rather reflect a degree of isolation of cavefish populations. Importantly, these populations are small, in the order of a few hundreds to a few thousands of individuals [35]. Therefore, we propose that the evolution of such acoustic signatures would be neutral and occur by drift, progressively leading to the differentiation of local accents that may ultimately prevent interbreeding and contribute to speciation.…”

“…Remarkably, in northeastern Mexico there are more than 30 caves where cavefish populations live [ 16 , 17 ]. They are all blind and depigmented but show signs of ongoing genetic differentiation in different caves [ 18 – 21 ]. The ecological conditions in different caves can be very variable [ 16 , 17 , 22 ].…”

A practical guide for the husbandry of cave and surface invertebrates as the first step in establishing new model organisms

“…Second, having a laboratory stock reduces the need for repeated removal of specimens from natural populations. This has positive implications on the protection and conservation of species with low population sizes or threatened or endangered status, often the original impetus to study these species [ 9 – 11 ]. Yet, protocols for the husbandry and successful breeding of non-model organisms are rare, because of the difficulties in establishing optimal conditions in the laboratory, and because triggers for reproduction are usually unknown.…”