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Dryad

Copulation interruption decreases female reproductive success in a false widow spider

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Nov 04, 2024 version files 71.91 KB

Abstract

Copulation is a necessary function for transferring sperm from males to females in most terrestrial animals. Its duration should be brief to minimize various costs but sufficient for fertilization of eggs. In the false widow spider, Steatoda grossa (Araneae: Theridiidae), undisturbed copulations typically last for 40-60 minutes. The adaptive function of this long copulation duration is unknown. However, as a common synanthropic spider, the likelihood of being disrupted by human activities is high. Therefore, we investigated reproductive success in S. grossa under a sequence of disrupted copulation duration (1 min, 3 min, 5 min, 10 min, 20 min) with a control treatment (i.e., uninterrupted mating). We found that within the first 5 minutes, disrupting copulation had a significantly negative effect on reproductive success (i.e., egg sac number and mass, spiderling number and aggregate body mass), and delayed production of the first egg sac (in some extreme instances by over 200 days). However, when copulation duration was 10 minutes or longer, reproductive outcome was not affected by copulation duration. We suggest that sperm transfer increases with copulation duration over the first 10 minutes. Copulation duration also did not influence the mean mass of spiderlings per egg sac, showing that copulation duration does not alter the content of ejaculates that can influence spiderling body mass. In the 1-minute treatment, offspring number and mass varied greatly among individuals which indicates considerable variation among males with respect to the speed and efficiency of sperm transfer. Extended copulation duration may be adaptive by influencing female receptivity, oviposition and fertilization processes. This study helps to elucidate the relationship between copulation duration and female reproduction and the costs and benefits of extended copulation on male and female fitness.