Resource assessment in hermit crabs: the worth of their own shell

Abstract

Animals gather information about the quality of a resource through its assessment and behave accordingly as a result of adaptive motivational changes. In the hermit crab Pagurus longicarpus, we investigated whether an individual was affected in its motivation to acquire a new shell by the quality of the domicile shell (own resource value [ORV]), of the offered shell (external resource value [ERV]), or of both and asked whether its motivation was altered by the information gathered during shell investigation. We analyzed the behavior of hermit crabs inhabiting shells of differing qualities and compared their willingness to acquire an offered shell—optimal, smaller than optimal, or larger than optimal—by measuring the latency to approach it, the number of shell investigation, and its total duration. Crabs in smaller shells (SSs) approached more quick and often the offered shell, whereas crabs in larger shells investigated the offered shell more thoroughly. The readiness of crabs to approach the offered shell and the extent of its investigation were independent of the ERV but were exclusively affected by the ORV, whereas the number and duration of shell investigation did not change with time as investigation proceeded, except for crabs in SSs. These results suggest that P. longicarpus' motivation to acquire a new shell is exclusively influenced by the value of the shell it inhabits rather than by the quality of the shell it is offered and that this species does not gather—or does not use—information about ERV during investigation.