Copulation interruption decreases female reproductive success in a false widow spider

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.

交配是多数陆生动物实现精子由雄性向雌性转移的必要生理过程。交配时长需尽可能短暂以降低各类代价，同时需足够完成卵子受精。在假寡妇蜘蛛（Steatoda grossa，Araneae: Theridiidae，即蛛形目：球蛛科）中，未受干扰的交配过程通常持续40至60分钟。该物种较长的交配时长的适应性功能目前尚不明确。然而，作为一种常见的伴人生物蜘蛛，其交配过程极易受到人类活动的干扰。因此，本研究针对假寡妇蜘蛛（S. grossa）设置了一系列打断后的交配时长处理组（1分钟、3分钟、5分钟、10分钟、20分钟），并以未打断的交配作为对照组，探究其繁殖成功率。研究结果显示，在前5分钟内打断交配过程，会对繁殖成功率（即卵囊数量与重量、幼蛛数量与总体重）产生显著负面影响，且会推迟首枚卵囊的产出时间（部分极端案例中延迟时长超过200天）。但当交配时长达到10分钟及以上时，交配时长则不会对繁殖结果产生影响。据此我们推测，在前10分钟内，精子转移效率随交配时长的增加而提升。交配时长同样不会影响每枚卵囊内幼蛛的平均体重，这表明交配时长并不会改变能影响幼蛛体重的射精液成分。在1分钟处理组中，不同个体的后代数量与体重存在显著差异，这表明不同雄性个体间的精子转移速度与效率存在较大差异。延长交配时长或许可通过影响雌性的接受性、产卵行为与受精过程，从而实现适应性优势。本研究有助于阐明交配时长与雌性繁殖间的关联，以及延长交配时长对雌雄个体适合度的利弊影响。