Morphological correlates of mating frequency and clutch size in wild caught female Eudiaptomus graciloides (Copepoda: Calanoida)

Abstract

A high proportion of female diaptomid copepods mate several times and more often than needed for each clutch production. Our understanding of the adaptive significance of this behaviour and the underlying process is limited. Theory suggests that polyandry may arise when whatever benefits females accrue from multiple mating outweigh the costs or, alternatively, that males manipulate females against the latter's best interests. We examined the relationship between female body size, clutch size and mating frequency, as indicated by the number of spermatophores in a wild caught copepod Eudiaptomus graciloides. Large females carried more eggs than small females. However, the frequency of mating (i.e. the number of spermatophores) was negatively related to the size of the female. Moreover, mating frequency was negatively related to the length of the antennules and positively related to the length of the furca. Diaptomid females are known to actively resist pursuing males by an escape reaction and their mobility and escape abilities are positively related to body size and antennule length. Consequently, large females might reject males more easily and hence mate less frequently than do small females. Our results suggest that multiple mating in E. graciloides is maintained by sexual conflict over mating rate, and that females are manipulated by males into additional meetings against their interests.