When to socialize: perception of time-sensitive social structures among social hermit crabs

Abstract

Animals have been specialized by natural selection to perceive features of their environment that strongly impact their reproductive success. For many social animals, the social world of conspecifics provides the most pertinent information, ultimately enabling individuals to adaptively anticipate future events, like time-sensitive opportunities to acquire rare resources. Here we investigated whether ‘social timing’—joining others at the right time for resource acquisition—ultimately drives the perception of different social structures among highly social terrestrial hermit crabs, Coenobita compressus. These crabs are specialized to live in architecturally remodelled homes, which can only be acquired through coordinated social interactions among conspecifics. We experimentally simulated these social interactions using static arrays of shells that mimicked the temporary social structures formed at each stage in the social shell-acquisition process. Free-wandering crabs in the wild were then allowed to choose among these different social structures. We found that crabs were most attracted to social structures representing early stages of the social shell-acquisition process, which predict forthcoming opportunities and hence allow individuals to join in time to take priority spots in ensuing social formations. In contrast, social structures representing late stages of the social shell-acquisition process were less attractive. When crabs joined such late-stage social structures they did not stay long, assessing they had arrived too late to insert themselves into the existing social arrangement. Broadly, these results suggest that strong selective pressures exist for sensory specializations that are in tune with the temporal and spatial patterning of opportunities in the social world.