Courtship and copula duration influence paternity success in a spider

Courtship can have multiple, nonexclusive, functions, and it often plays a central role in mate choice. In the polyandrous, cannibalistic spider Argiope keyserlingi, males perform vibratory courtship that suppresses female aggression. Although females appear to have a preference (i.e. they shorten their latency to mate) for males performing courtship displays with specific characteristics (i.e. many shudders with consistent shudder duration), they are not more likely to mate with them. Here, we asked whether in this species courtship quality plays a role in postcopulatory sexual selection, by affecting male fertilization success via cryptic female choice. We quantified male courtship performance in a standardized thread assay with no male–female interactions, which simulates male approach to the female on the web. We allowed each unmated adult female to mate with two males. Prior to mating, one male from each pair was sterilized using an irradiation treatment and offspring paternity was assigned using the sterile male technique. Unexpectedly, we found that irradiated males had a fertilization advantage over nonirradiated males. When we controlled for that bias, males performing courtship with a large number of shudders and long copula durations gained the largest paternity shares. Together with evidence from previous studies, our results suggest that courtship quality mediates cryptic female choice, but further investigations are needed to parse out the influence of female control and sperm competition on paternity.