No material benefits, and a fertilization cost, for multiple mating by female leaf beetles

When females mate multiple times it presents an intriguing problem for evolutionary biologists due to the high costs and not very apparent benefits. Yet, this behaviour must have higher benefits than costs to be maintained by natural selection. We studied possible benefits for multiple mating by female leaf beetles, Leptinotarsa decemlineata, both with multiple males (polyandry) and multiple times with the same male (repeated matings). For polyandry, we tested the material benefits hypothesis, as well as fertility insurance, by mating females to varying numbers of males and looking at sperm received and fecundity. Although there was a relationship between amount of stored sperm and number of matings, we did not find the predicted positive relationship between fecundity and number of matings. Thus, the material benefits hypothesis was not supported. For repeated matings, we tested the sperm and nonsperm material benefit hypotheses by mating females to a single male varying numbers of times on one mount. For this set of tests neither sperm number nor fecundity was positively correlated with number of matings, therefore neither hypothesis was supported. Interestingly, in both experiments, there was a significant decrease in hatch rate with an increase in matings, demonstrating a cost of polyandry. These findings, along with previous research, suggest a cost of multiple mating with a possible role of seminal fluids in the reduction in female fecundity.