Influence of environmental stress on age- and size-at-maturity: genetic and plastic responses of coastal marsh fishes to changing salinities

Abstract

As sea levels rise, salt water will intrude into freshwater coastal habitats with greater frequency and stress resident organisms inducing physiological trade-offs that influence life history tactics. Western mosquitofish ( Gambusia affinis ) and least killifish ( Heterandria formosa ), collected along a salinity gradient and maintained in a common freshwater environment for two years (≥4 generations), were used to examine historical (genetic effects) and contemporary environmental effects of salinity on age- and size-at-maturity. There was phenotypic plasticity for sexual maturation and genetic variance among source populations for size-at-maturity, but no genetic variance for plasticity itself as indicated by the lack of genetic-by-environment interactions. Gambusia affinis males and H. formosa females exhibited stress by maturing at smaller sizes and older ages in response to being reared in 0 and 12 ppt, respectively. Our results suggest that habitats in which these fishes are most abundant do not correspond to the salinities at which they can rapidly mature at larger sizes, indicating that other environmental factors are also influential to their distribution and abundance along salinity gradients.