Astyanax cavefish body shape coordinates from: Phylogeographic relationships and morphological evolution between cave and surface Astyanax mexicanus populations (De Fillipi 1853) (Actinopterygii, Characidae)

The Astyanax mexicanus complex includes 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 reflecting the most divergent morphology
relative to surface and other cavefish populations.