Predation upon pelvic phenotypes of brook stickleback, Culaea inconstans, by selected invertebrates

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Abstract
Laboratory experiments investigated selective predation by aquatic insects upon phenotypes of brook stickleback (Culaea inconstans), with and without pelvises, from Wakomao Lake, Alberta, Canada. Predation by Lethocerus americanus (water bug) and nymphs of Aeschna spp. (dragonflies) was random upon each phenotype. Predation by the larvae of Dytiscus spp. (water beetle) resulted in significant selection for with individuals possessing five dorsal spines. The observed selection was at least partially due to closer approaches to the predator made by the withs. No selection occurred for either phenotype with six dorsal spines. This evidence supports an hypothesis that the pelvic variation is maintained by differential predation.