Sociosexual environment influences patterns of ejaculate transfer and female kicking in Callosobruchus maculatus

There is growing evidence that many organisms adjust their physiology and behaviour during sexual encounters according to changes in their sociosexual situation. Selection tends to favour plasticity in males that can strategically ejaculate and females that can alter their resistance or remating behaviour adaptively. We investigated plasticity both in the ejaculate transfer patterns of males and in the pericopulatory kicking behaviour of female seed beetles, Callosobruchus maculatus. We altered the sociosexual environment of the beetles by (1) manipulating male mating history, (2) preventing females from kicking and (3) altering the risk of sperm competition. Males mating for the second time transferred half the weight of ejaculate of virgin males, but at the same rate. Males mating in the presence of rivals did not alter the weight of ejaculate, as might have been expected; however, the transfer of ejaculate began sooner. By looking at the effect of female kicking on male ejaculate transfer, we found that when females have their hindlegs ablated to prevent kicking, the rate of ejaculate transfer slows, but the weight remains the same. From the female perspective we found that the probability of females kicking was positively related to both copula duration and ejaculate weight, but also to male mating history; females were less likely to kick males that had mated more times previously even after controlling for copula duration and ejaculate weight. Finally, we found that removing a female's hindlegs increased the probability that females (attempted to) kick. Our results show that males are, to some extent, plastic in their ejaculatory responses to the sociosexual environment. More striking, however, and not previously documented, is that female kicking is affected by environmental variables, including male mating history.