Interacting effects of developmental temperature and source population on the phenotype of Gambusia marshi

Authors: Moody, Eric K.*, Corman, Jessica R., Espinosa-Perez, Hector, Ramos, Jorge, Sabo, John L., Elser, James J.

Year: 2015 (xlvii)

Abstract

The robust gambusia, Gambusia marshi, is native to the Río Salado basin in Coahuila, Mexico. This species inhabits a wide variety of habitats including rivers, thermal springs, and evaporative wetlands. In his description of G. marshi, W.L. Minckley suggested that phenotypic variation in fish among these habits may represent a species complex rather than a single variable species. We aim to investigate the source of phenotypic variation in G. marshi, focusing specifically on fish inhabiting springs in the Cuatro Ciénegas basin. Among eight springs, we found that adult female body size is negatively correlated with temperature, and that fish from warmer springs differ in their elemental composition and excretion ratios. We conducted a geometric morphometric analysis on specimens from two cool and two warm springs, and found a significant interacting effect of temperature and sex on fish morphology. We then reared F1 fish from two populations, La Becerra (mean temp = 32 C) and Los Hundidos (mean temp = 25 C), at both temperatures in the laboratory. Within each population, 25 day-old fish were smaller when reared at 33 C than at 25 C. However, fish from La Becerra were smaller at birth than fish from Los Hundidos, and this difference persisted in 25 day-old F1 fish. Further, we found significant interacting effects of source population and developmental temperature on consumption, respiration, and excretion N:P of 25-day old fish. Our results suggest that while genetic differences between populations may affect the phenotype of G. marshi, thermal differences among springs also cause phenotypic plasticity.