INTRA-POPULATION VARIATION IN HYDROBIA SEDIMENT PREFERENCES

Contrary to earlier supposition, the small intertidal gastropod Hydrobia ulvae has recently been shown to exhibit marked behavioural preferences for muddy sediments when provided with a choice of substrata (Barnes & Greenwood, 1978). As generally seen in preference experiments, however, not all individual snails necessarily select mud in any given trial: some (c. 10-15% in these experiments) occur on the generally-avoided sand alternative. Although usually dismissed as chance strays or individuals in transit, some of these recalcitrant individuals selected sand as a result of a definite, though atypical, preference for sandy substrata. Hydrobia populations-and presumably those of other species as well-are not therefore uniform in respect of these behavioural responses. © 1979.