Multiple traits and multifarious environments: integrated divergence of morphology and life history

Understanding complex responses of multiple character suites (e.g., behaviour, life history, morphology) to multifarious environments is a challenging task. Here we use a multivariate approach (partial least squares structural equation modelling) to disentangle drivers (i.e., predation, resource availability, and population demographics) of phenotypic divergence among populations of Bahamas mosquitofish (Gambusia hubbsi) inhabiting blue holes. We further employ a two-block partial least squares analysis in a novel approach to uncovering integrated and independent aspects of divergence in correlated character suites. Results suggest that phenotypic divergence mainly resulted from differences in predation regimes, with population demography and resource availability also influencing particular aspects of divergence. We uncovered statistically significant covariation of life histories and morphologies, and revealed that phenotypic divergence between predation regimes involved both integrated and independent responses. For instance, female life histories diverged mostly independently of morphology, although some morphological shifts (abdominal distension) resulted from changes in fecundity. In contrast, males showed strong morphological divergence independent of life history, but much of their life-history shifts reflected joint morphological changes (lean weight and body shape). Our study illustrates the utility of gathering disparate data types from multiple populations/species to understand the causes and nature of phenotypic divergence in the wild.