Meeting Abstract
The physical appearance (i.e. body shape) of a species is both a target of selection and ecologically important. Investigating body shape variation along environmental gradients lends itself to understanding the factors that exert selection and drive evolutionary changes in morphology. Rivulus hartii, a species of killifish, is found across a gradient in predation and competition in streams on the island of Trinidad. Previous work using field specimens revealed phenotypic differences, with high predation populations having an unsteady body shape and more fusiform body shape in Rivulus only populations. We tested for a genetic basis underlying phenotypic differences in body shape. Second-generation lab reared Rivulus from divergent predation and competition regimes were reared till maturation on two levels of food that mimic naturally occurring variation in the wild. Body shape was analyzed using landmark geometric morphometrics with 19 landmarks. We found that body shape differed as a function of river of origin and food availability; individuals reared on low food levels exhibited a broader head and slightly narrower body, indicating a potential investment in a larger mouth to increase resource acquisition. Importantly, difference in body shape among populations from contrasting predator communities paralleled previous phenotypic trends but were weaker in magnitude. Our results reveal important roles for genetic and environmental effects on the expression of morphological characteristics.
