Intra- and interpopulation variation in morphology and behaviors in the sailfin molly, Poecilia latipinna (Poeciliidae: Poecilia: Mollienesia)

Understanding factors that contribute to population differences can provide insight into the process of speciation, yet population level studies seldom take into account variation among individuals within a population. Such intrapopulation variation may influence the degree to which interpopulation variation in suites of traits can arise. My research focused on characterizing intra- and interpopulation variation in male morphological and behavioral traits in the sailfin molly, Poecilia latipinna. First, I characterized the overall body shape of several populations of P. latipinna collected from north Florida in two different years. I used linear morphological measurements to examine shape and found there to be population differentiation within each sampling year, but some of the traits that explained this variation differed between sampling years. Males were more often correctly classified back into their original populations in 2005 (72% correctly assigned) than in 2007 (67% correctly assigned), suggesting variability between years in the degree of morphological differentiation. Second, I generated unique behavioral profiles for males from three of these populations in three distinct behavioral contexts: mating, activity, and inspection. I tested males in two situations per context: mating (with a receptive vs. a non-receptive female) activity, (after viewing a social group vs. a predator) and boldness, (inspecting a conspecific social group vs. a predator). I found that male sailfin mollies showed (1) strong positive associations between situations within a context, (2) strong positive associations between courtship display rates and level of boldness in predator inspection, and (3) no significant differences in behaviors between populations. Male size at maturity (known to have a Y-linked genetic basis) was strongly positively associated with courtship display rates and boldness but not activity. These findings suggest that mollies may possess a behavioral syndrome where larger males are bolder toward predators, court females more vigorously and have proportionately larger dorsal fins. Thus, variation among individuals within populations in these associated traits may be slowing the degree of differentiation in behavior among populations despite interpopulation variation in body shape.