Reason for being single: some males do not guard receptive females in the hermit crab Pagurus filholi

Abstract

In animals that reproduce sexually, males are often under strong selection to maximize the number of mating opportunities. However, in some iteroparous species, males do not always maximize the allocation of time and energy to the present mating opportunity. Male hermit crabs of the genus Pagurus show precopulatory guarding as a mate acquisition strategy. Although almost all males within this genus guard and compete for receptive females, males of Pagurus filholi differ in how likely they are to do so. To examine the factors explaining the absence of guarding behaviour in P. filholi, a laboratory experiment was conducted that focused on whether either of two receptive females was guarded by solitary males that had been found not paired in the field, had lost a previous male–male contest or had copulated with other females. Solitary males showed a significantly lower frequency of guarding than males with experience of losing or of copulation. In the solitary group, males that moulted within 5 days after the experimental trial did not guard females, and the moulting frequency of nonguarding males was significantly higher than that of guarding males. In further analysis, smaller solitary males were shown to be less likely to guard females. The results of the experiment suggest that males of P. filholi may not always invest as much as possible in the present mating opportunity but may temporarily invest in growth during the 8-month mating season.