Dietary induction of opisthobranch morphology: Placida dendritica (Alder and Hancock, 1843) on different green algal hosts

Abstract

The relationship of phenotypic morphological and behavioural variation was investigated for the ascoglossan (-sacoglossan) opisthobranch Placida dendritica. Morphological attributes were documented for individual slugs collected from three algal host species along the central Oregon coast, USA, the green algae Codium setchellii, C. fragile, and Bryopsis corticulans. Because individuals on B. corticulans generally were substantially larger than conspecifics on Codium spp., the species appeared polymorphic. Comparably sized slugs from different host genera also differed significantly in morphology: individuals from Codium spp. had more numerous, shorter cerata on wider bodies than did conspecifics from B. corticulans. Principal components analysis indicated that despite considerable overlap of morphological characters, ceratal shape features were diagnostic of algal host. When slugs collected from C. fragile were maintained on C. fragile and B. corticulans for 4 days in the laboratory, the size and shape of slugs fed different diets diverged, and changes were consistent with field data. Thus, phenotype was labile and changed as a result of modified diet. Although a variety of molluses exhibit dietary induction of morphology, a general awareness of the phenomenon has only recently begun to emerge, despite its important ecological and taxonomic implications.