Copulation interruption decreases female reproductive success in a false widow spider

Abstract Copulation is essential for transferring sperm from males to females in most animals. During copulation, males and females are often static and thus prone to predation or other threats. Its duration should therefore be reduced to minimize costs but sufficient to ensure the fertilization of eggs. Here, we investigated reproductive behavior and success in the false widow spider, Steatoda grossa (Araneae: Theridiidae), when copulation was interrupted after 1, 3, 5, 10, or 20 min or was not experimentally interrupted (control). Copulation duration in this study is defined as the total duration of insertions of male pedipalps into a female’s copulatory openings. In S. grossa , uninterrupted copulations typically last 40 to 60 min. We found that within the first 5 min, copulation interruption negatively affected reproductive success (i.e., number of egg sacs, their total mass, and number of spiderlings), and delayed production of the first egg sac within the first 10 min (in some extreme instances by over 200 days). However, when copulation duration was 10 min or longer, reproductive outcome was unaffected. In the 1-min treatment, the number of egg sacs and their mass varied greatly, which indicates considerable variation among males with respect to the speed and efficiency of sperm transfer. We discuss the costs and benefits of extended copulation duration on female reproduction and on male and female fitness.