Phylogeographic relationships and morphological evolution between cave
and surface Astyanax mexicanus populations (De Fillipi 1853)
(Actinopterygii, Characidae)
Abstract
The Astyanax mexicanus complex include two different morphs, a surface
and a cave adapted ecotype, found at three mountain ranges in
Northeastern Mexico: Sierra de El Abra, Sierra de Guatemala, and Sierra
de la Colmena (Micos). Since their discovery, multiple studies have
attempted to characterize the timing and the number of events that gave
rise to the evolution of these cave-adapted ecotypes. Here, using
RAD-seq and genome-wide sequencing, we assessed the phylogenetic
relationships, genetic structure, and gene flow events between the cave
and surface Astyanax mexicanus populations, to estimate the time and
mode of evolution of the cave-adapted ecotypes. We also evaluated the
body shape evolution across different cave lineages using geometric
morphometrics to examine the role of phylogenetic signal vs.
environmental pressures. We found strong evidence of parallel evolution
of cave-adapted ecotypes derived from two separate lineages of surface
fish and hypothesize that there may be up to four independent invasions
of caves from surface fish. Moreover, a strong congruence between the
genetic structure and geographic distribution was observed across the
cave populations, with the Sierra de Guatemala the region exhibiting
most genetic drift among the cave populations analyzed. Interestingly,
we found no evidence of phylogenetic signal in body shape evolution, but
we found support for parallel evolution in body shape across independent
cave lineages, with cavefish from the Sierra de El Abra reflected the
most divergent morphology relative to surface and other cavefish
populations.