Data from: Predation drives morphological convergence in the Gambusia panuco species group among lotic and lentic habitats

Fish morphology is often constrained by a trade-off between optimizing
steady vs. unsteady swimming performance due to opposing effects of caudal
peduncle size. Lotic environments tend to select for steady swimming
performance, leading to smaller caudal peduncles, while predators tend to
select for unsteady swimming performance, leading to larger caudal
peduncles. However, it is unclear which aspect of performance should be
optimized across heterogeneous flow and predation environments and how
this heterogeneity may affect parallel phenotypic evolution. We
investigated this question among four Gambusia species in northeastern
Mexico, specifically the riverine G. panuco, the spring endemics G.
alvarezi and G. hurtadoi, and a fourth species, G. marshi, found in a
variety of habitats with varying predation pressure in the Cuatro Ciénegas
basin and Río Salado de Nadadores. We employed a geometric morphometric
analysis to examine how body shapes of both male and female fish differ
among species and habitats and with piscivore presence. We found that
high-predation and low-predation species diverged morphologically, with G.
marshi exhibiting a variable, intermediate body shape. Within G. marshi,
body morphology converged in high-predation environments regardless of
flow velocity, and fish from high-predation sites had larger relative
caudal peduncle areas. However, we found that G. marshi from low-predation
environments diverged in morphology between sub-basins of Cuatro Ciénegas,
indicating other differences among these basins that merit further study.
Our results suggest that a morphological trade-off promotes parallel
evolution of body shape in fishes colonizing high-predation environments
and that changing predation pressure can strongly impact morphological
evolution in these species.