Developmental dimorphism and expression of chemosensory-mediated behavior:Habitat selection by a specialist marine herbivore

Developmental dimorphisms provide an opportunity to compare sensory systems and behavior patterns between different forms of a single species. Alterna tive morphs differing in dispersal ability often show behavioral difference s that mediate life-history trade-offs. We measured the behavioral response s of both long-lived, feeding larvae and short-lived, non-feeding larvae of the specialist marine herbivore Alderia modesta during habitat selection. Larvae immediately responded to waterborne cues from the adult host algae b y increasing their turning rate, by changing their swimming speed in the wa ter and by moving in rapid hops or spiraling along the bottom. These behavi or patterns retained larvae in areas where the dissolved cue was initially perceived, and prolonged exposure to the cue increased the percentage of la rvae that initiated metamorphosis. Despite their differences in life span a nd trophic mode, both larval morphs displayed similar behavior patterns whe n stimulated by the waterborne cue. Long-lived larvae had a stronger respon se, however, suggesting that settlement behavior may offset the costs of a prolonged larval life. This is the first study to examine the effects of di morphic development on chemosensory-mediated behavior.