Diet Specialization Limits Herbivorous Sea Slug's Capacity to Switch Among Food Species

Abstract

Sympatric, conspecific animals may use resources in different ways: a population of foragers with a generalist diet may be composed of polyphagous individuals or of different types of oligophagous individuals. The sea slug Placida dendritica (Opisthobranchia: Ascoglossa) exhibited the latter pattern. Individuals slugs from different green algal host species exhibited different rank preferences of and performances on host species. Feeding preferences did not change through time and were independent of Placida size. In addition, the slug's highly rigid feeding specificity was not modified through hunger level, algal condition, or social interactions with experienced conspecifics. Thus, Placida frequently died when maintained on "unfamiliar" host species that sympatric conspecifics consumed. The extreme trophic specialization of Placida suggests that the costs of switching host species may be extremely high in short—lived foragers.