THE OLFACTORY-GUSTATORY BASIS OF FOOD PREFERENCE IN THE HERBIVOROUS PROSOBRANCH, <i>LITTORINA LITTOREA</i> (LINNAEUS)

Abstract

Studies of food preference often measure the rate of consumption of prey items by a predator; this confounds the factors determining attractiveness and edibility, ignoring the fact that preferences are probably resolved at the pre-ingestive stage of a consumer's feeding behaviour. In this paper, a novel technique has been developed to measure the importance of chemical stimuli to feed, perceived by olfactory and gustatory means, as determinants of the subsequent feeding behaviour of the generalist intertidal herbivore,Littorina littorea (L.). Cell-free extracts of a range of algae were presented simultaneously, impregnated in artificial cellulose-based substrates. Subsequent ranking of feeding preferences reveals hierarchies which correspond with those established by other workers, using intact algae to feed L. littorea. Extracts of ephemeral early successional species (e.g. Ulva lactuca, Porphyra umbilicalis) generally provoke a more positive feeding response than perennial late successional species (e.g. Fucus vesiculosus, Asco-phyllum nodosum). Animals fed a preferred alga (Ulva lactuca) prior to preference trials displayed a reduction in the strength of preference relative to starved animals. There was no evidence of ‘switching’ of preference rankings due to satiation, however. These findings confirm the importance of olfactory-and gustatory-mediated feeding behaviour as the primary determinant of food preference in L. littorea. They are consistent with the hypothesis that the factors which determine the attractiveness of a food type, such as chemical cues, are the criteria by which consumers predict the value of that food.