Sperm removal, ejaculation and their behavioural interaction in male cuttlefish in response to female mating history

The removal of previously stored rival sperm and increased ejaculate expenditure are effective male sperm competition tactics to ensure paternity. We examined both behaviours and their interaction for male cuttlefish, Sepia lycidas , as a strategic investment. Males increased the duration of sperm removal and the number of ejaculations per mating when they were not the last male who had mated with the current partner. These responses would decrease the number of rival sperm and increase the male's own sperm in the fertilization area. Recognition of the female's mating history appeared to result from close mate guarding during successive matings. Moreover, when the last mate of the current partner was different from the current mate, there was a significant negative relationship between sperm removal duration and the number of subsequent ejaculations. This interaction suggests both strategic investment allocation and constraints on each mating investment as possible results of mating interruption by other males and spermatophore depletion, respectively. In addition, larger males with high competitive ability prolonged sperm removal when the last mate of the current partner was different from the current mate, whereas smaller males with relatively larger testes ejaculated more times during a mating. Male S. lycidas might adjust the duration of sperm removal at the risk of failing to achieve ejaculation and allocate their finite ejaculate expenditures based on the results (i.e. the increasing proportion of their own sperm).