Predation shapes morphology of spring Gambusia in Northeastern Mexico

Authors: Eric Moody, Maria de Lourdes Lozano-Vilano

Year: 2016 (xlviii)

Abstract

Perennial limnocrene springs represent unique environments in arid landscapes due to their more lentic nature, environme ntal stability, and often, a lack of piscivorous fish. In the Chihuahuan desert, numerous limnocrenes have been colonized by fishes such as Gambusia. Over time, these populations diverged genetically and phenotypically from riverine ancestors, but it is no t clear what drives this phenotypic divergence. We investigated this question in the Gambusia panuco species group, which includes 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 and without predators. We employed a geometric morphometric analysis to examine how body shape of both male and female fish differs among species, habitats, and predation pressures We found that riverine and spring species diverged morphologically, with G. marshi exhibiting a variable, intermediate body shape. Within G. marshi, morphological variation was explained by piscivore presence in both sexes but by habitat type only in males, suggesting that predators exert a stronger selective force on Gambusia morphology among both sexes but that males also respond to differences in the physical environment. Further supporting this notion, fish from sites with piscivores present had larger caudal relative peduncle areas. We also found that sexual dimorphism in size was higher in spring environments among species regardless of predator presence, indicating that some sexual constraints on morphology may exist. These results are of particular importance because many desert spring fishes are threatened by declining groundwater levels and introduced species, both of which could alter the morphology of these fish if they persist under alter ed environmental conditions.