The role of calceoli in mate assessment and precopula guarding in Gammarus

Gammarid crustacea exhibit precopula mate guarding in which a male will carry a potential mate beneath his ventral surface, guarding her for several days until she moults and lays her eggs. I investigated the role of the calceoli (bulb-like structures on the second antennae) in mate assessment and precopula pairing in two Gammarus species by comparing the behaviour of males with and without calceoli. Removal of the calceoli had no effect on the pattern of size-assortative mating, nor did it reduce the number of contacts made per unit time between potential mates. However, males without calceoli reduced their assessment of potential mates, were less likely to guard a suitable female and guarded for a shorter period. These data support the hypothesis that calceoli are used during contact assessment to determine a female's intermoult period and hence suitability for guarding. (C) 1998 The Association for the Study of Animal Behaviour.