LESS CHOOSY OR DIFFERENT PREFERENCE - IMPACT OF HYPOXIA ON HERMIT-CRAB SHELL ASSESSMENT AND SELECTION

Hermit crabs that rely on gastropod shells for protection have to asse ss a number of shell features, each of which can bring different, and sometimes conflicting, advantages to their bearer. We examined how env ironmentally induced stress, in the form of hypoxia, can alter the rel ative benefits of different shell features and result in the selection of different shells by the hermit crab Pagurus bernhardus. Hermit cra bs under hypoxic conditions spent significantly less time investigatin g shells before entering them. Despite this apparently superficial ass essment, they chose shells that were well suited to hypoxic conditions ; After 24 h, they were found in shells that were significantly lighte r than those chosen by hermit crabs under normal oxygen. This shift in preference was achieved at the expense of the internal spaciousness o f the shell, which may have deleterious implications for predation and reproduction. This cost was more evident for larger hermit crabs sinc e there was no relationship between hermit crab size and shell charact eristics for hermit crabs in hypoxia. Under oxygen stress, hermit crab s therefore alter their shell preference in favour of lighter, and thu s smaller, shells, probably reflecting a greater concern for energy mi nimization than protection from predation or reproduction. (C) 1998 Th e Association for the Study of Animal Behaviour