Gergely Horváth, Sára Sarolta Sztruhala, Gergely Balázs, Gábor Herczeg

Aggregation (gathering together) and sheltering (hiding in cover) are basic behaviours that might reduce the risk of predation. However, both behaviours have costs, like increased competition over resources and high prevalence of contact-spread parasites (aggregation) or lost opportunities for foraging and mating (sheltering). Therefore, adaptive variation in these behaviours is expected between populations with varying levels of predation risk. We compared aggregation and sheltering in surface- (various predators) and cave-adapted (no predator) populations of the Isopod Asellus aquaticus in a common garden experiment. Since the cave environment is constantly dark, we also tested for population variation in light-induced behavioural plasticity by applying light treatments. Variation in sheltering was explained by habitat type: cave individuals sheltered less than surface individuals. We found high between-population variation in aggregation with or without shelters and their light-induced plasticity, which were unexplained by habitat type. Cave individuals habituated (decreased sheltering), while surface individuals showed sensitization (increased sheltering). We suggest that population variation in sheltering is driven by predation, while variation in aggregation must be driven by other, unaccounted environmental factors, similarly to light-induced behavioural plasticity. Based on habituation/sensitization patterns, we suggest that predation-adapted populations are more sensitive to disturbance related to standard laboratory procedures.