Silk-borne chemicals of spider nuptial gifts elicit female gift acceptance

Chemical communication is important in a reproductive context by conveying information used for mate recognition and/or assessment during courtship and mating. Spider silk is common as vehicle for chemical communication between the sexes. However, despite being well described in females, male silk-borne chemicals remain largely unexplored. Males of the spider Pisaura mirabilis silk-wrap prey (i.e. nuptial gifts) that is offered to females during courtship and eaten by the female during copulation. Interestingly, rejected males often add more silk to their gift which leads to mate acceptance, suggesting presence of silk-borne chemicals that facilitate female gift acceptance. To test this hypothesis, we offered females standardised gifts covered with male silk that was either washed in solvents or unwashed, respectively to remove or not any chemically active components. We scored female gift acceptance, and as expected in the case chemicals that mediate female mating behaviour are present in male silk, females were more likely to accept gifts covered with unwashed silk. Our findings suggest that silk-borne chemicals of nuptial gifts prime female responses, potentially signalling male quality or manipulating females into mating beyond their interests given the occurrence of male cheating behaviour via nutritionally worthless gifts in this system.