Male spiders reduce pre- and postmating sexual investment in response to sperm competition risk

The interplay between pre- and post-mating responses to intra-sexual competition remains enigmatic. Sperm competition models often assume a trade-off between pre- and post-mating traits that enhance mate acquisition and fertilization success, respectively. However, when males court females through food donations (i.e. nuptial gifts), pre- and post-mating responses may be aligned, as nuptial gifts have the dual function of facilitating both mate acquisition and sperm transfer. In the spider Pisaura mirabilis nuptial gifts consist of silk-wrapped prey. We tested whether males respond to a competitor by altering: 1) pre-mating investment in the gift; 2) post-mating sperm investment; and 3) whether pre- and post-mating responses are coupled and respond to competition in the same direction or not. Under competition risk males silk-wrapped their gifts for significantly shorter time and transferred less sperm to females, pointing to a reduction of both pre- and post-mating responses. Since sil...