Bloodmeal size defines ejaculate production and impacts on male mating behaviour in Cimex lectularius.

Reproductive costs have been investigated mainly in females, even though males certainly also pay such costs. As nutrition provides the basis for the production of biomass and reproductive tissues, variation in food availability might cause variation in sperm and seminal fluid production. Therefore, we can assume that meal size might be directly associated with ejaculate size. Here we analysed the production of sperm and seminal fluid within three different feeding regimes in six different populations with the result that large meals produced significantly more sperm and seminal fluid than small meals or no meals at all. While the number of offspring produced after a single mating was not influenced by feeding status, copulation duration and the ejaculate expenditure were shorter respectively smaller with restriction to food. Under food restriction males could maintain mating for a shorter time than fully fed males, suggesting in a multiple mating context males might pay a cost of reproduction. These results illustrate that there is a direct effect of feeding on sperm and seminal fluid production and male mating behaviour. Therefore, environmental variation, e.g. food availability, has a direct effect on variation in male reproductive traits, which indicates that natural selection and sexual selection will interactively define selection pressure on reproductive traits. As males often modulate their ejaculate size depending on the mating situation, future studies are needed to elucidate whether the amount of ejaculate available might interfere with different mating strategies.