Natural selection by avian predators on size and colour of a freshwater snail (Pomacea flagellata)
WENDY L. REED* AND FREDRIC J. JANZEN
Department of Zoology and Genetics, Iowa State University., Ames IA 50011, U.S.A.
We identify two avian predators of the Neotropical apple snail, Pomacea flagellata, and estimate the strength, direction and form of multivariate natural selection by these predators on size and colour of snail shells. Limpkins are tactile predators and act as agents of disruptive selection on snail size, selecting average-sized snails disproportionately more often than small or large snails (y'=0.39, SE=0.08). In addition, we were able to identify variation in handling behaviours and snail size selection among individual limpkins. Individual limpkins showed preferences for snails of different sizes and punctured the snail shells opposite the aperture mainly when handling large snails. Snail kites are visual predators and seem to be agents of directional selection against lighter coloured snails (B'=0.66, SE=0.33). The ecological interaction between the apple snail and its predators provides a powerful system to further explore the role of predation in determining evolutionary changes in snail behaviour, morphology and life history.
Biological Journal of the Linnean Society (1999), 67: 33 1 342.