Activity and shelter use of an intertidal snail: effects of sex, reproductive condition and tidal cycle

Although activity patterns are an important component of the ecology of animals as they search for food, mates and appropriate habitats, substantial variation can be observed even within a single population. The source of this variation is the combination of intrinsic and extrinsic factors acting at an individual level. We documented the activity patterns of the ovoviviparous intertidal gastropod Littorina saxatilis (Olivi) over a series of tidal cycles to assess how differences in movements of individuals with different reproductive attributes (non-gravid females, gravid females and males) might explain intra-population variability in activity. Four behaviors were measured for four consecutive tidal cycles for each of 3 months: the magnitude, frequency, and orientation of movements, and the use of shelters (i.e., crevices). In addition, we correlated movements with variations in several environmental factors (temperature, wind, humidity) during low tide to investigate the possible risk sensitivity of the different reproductive groups. All groups were more active and moved greater distances during high tide. Females, especially gravid females, appeared to be more risk-sensitive as they moved shorter distances and used shelters more often. Gravid females were also the only group with a negative relationship between air temperature and movement during low tide. We interpret these behaviors as a means to increase the probability of survival of the brooded offspring carried by the female. Males were the only group to consistently have directionality in their movements and showed evidence of an “up-down” behavior for remaining in a restricted zone. Reproductive attributes appear to be able to explain part of the intra-population variability in foraging activity in natural populations and should be taken into account in the design and interpretation of behavioral and ecological studies.