DOI: 10.5061/dryad.k98sf7mcn
title: Copulation interruption decreases female reproductive success in a false widow spider

description: 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.
description: # Copulation interruption decreases female reproductive success in a false
 widow spider
 [https://doi.org/10.5061/dryad.k98sf7mcn](https://doi.org/10.5061/dryad.k98sf7mcn) ## Description of the data and file structure We assigned spiders to one of the following five copulation interruption treatments, i.e., interruption after 1 (n = 15), 3 (n = 16), 5 (n = 16), 10 (n = 15), or 20 min (n = 16), and a control treatment (with no interruption, n = 16). One unrelated male was introduced into the box with a female. The pair of spiders was observed during the entire copulation trial. It was visually observed when copulation was initiated, i.e., when the male successfully inserted one of the pedipalps into the female copulation organ. Typically, when mating is not interrupted, males alternate pedipalp insertions three of four times (Dong et al, 2023). Individual palp insertions last 15 to 30 min (personal observation). In the mating interruption trials that lasted 10 min or less, males only inserted one palp into the female’s reproductive organ, whereas both palps were inserted or alternated palp insertions occurred in the 20-min and control trials. All mating pairs copulated. Between palp insertions, mating pairs separated and additional palp insertion were preceded by renewed courtship behavior. Mating was terminated by tapping the box manually or by gently touching the web around the in-copula pair using forceps. In a control group, mating was allowed to proceed until it was terminated naturally by either the male or the female. After mating, males were removed from the boxes, while females were left undisturbed and were subsequently provided with one house cricket nymph (*A. domesticus*, 6th instar) as food per week until the end of the experiment. Boxes with mated females were monitored daily for egg sac production until the female died or no more egg sacs were produced within 6-months since the last egg sac was produced. Egg sacs were removed from the boxes by gently cutting the silk threads with micro-scissors, weighed on a Mettler-Toledo Microbalance MT5 (accuracy 0.001mg, Columbus, Ohio, USA), and placed individually in Petri dishes (8 cm diameter). The dishes were maintained in a climate chamber set at 22 ± 2℃ during daytime and 12 ± 2℃ during nighttime, a relative humidity of 60%, and a 16:8 light-dark photoperiod. Females occasionally lay sterile egg sacs. If egg sacs were viable, the number of spiderlings that hatched from them was counted and spiderling counts were summed across all egg sacs to give total viable offspring production per female. In addition, the time interval between mating and production of the first egg sac was recorded. Eight females in the 1-min-copulation treatment produced only few and 6 females produced no egg sacs at all, whereas the other copulation-interruption treatments had no or only marginal effects on reproduction. To test whether reduced egg sac production was caused by sperm limitation, we conducted a small additional experiment (we had only few females available to test this). Females from the 1 min copulation treatment were allowed to remate with a virgin mature male after more than 6 months of reproductive inactivity and were monitored for egg sac production for an additional 3 months. Females from the control treatment which produced multiple egg sacs and did not produce a new egg sac for at least 6 months (5 out of 16 in total) were also allowed to remate. In addition, we tested whether short copulation and uninterrupted mating affected receptivity to a second male. Young virgin females taken from the rearing were allowed to copulate for 10 min (n=5), as described previously, or were allowed to copulate without interruption (n=6). Females from both groups were allowed to remate the following day with another virgin male. As females in both treatments readily remated, this experiment was not repeated further. ### Files and variables #### File: mating\_disruption\_data.xlsx | Column Heading Discriptors for Sheet 1 and Sheet 2: | | :-------------------------------------------------- | | **female\_number** | the female number, "unique ID" | | :--------------------- | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | mating\_date | the date that mating occurred, yyyy-mm-dd | | male\_mass | body mass of male, unit/mg | | treatment | the category of different treatment, it refers to different copulation duration which were interrupted physically, A=1 min, B=3 min, C= 5 min, D= 10 min, E= 20 min, F= Control, Control means undisrupted copulation. All equations work vise versa. | | copulation\_duration | the duration of copulation, unit/minutes | | death\_date | the date of female death, yyyy-mm-dd | | courtship\_duration | the duration from introducing the male to female's place to copulation occurs, unit/minutes | | lay\_dateX | the date of the Xth egg sac laid from the female, yyyy-mm-dd | | eggsac\_massX | the weight of the Xth egg sac, unit/mg | | hatch\_dateX | the hatching date of the Xth egg sac, yyyy-mm-dd | | amount\_spiderlingX | the amount of spiderling hatched from the Xth egg sac | | mean\_weightX | the mean weight of spiderling hatched from the Xth egg sac, mean weight = total weight/amount of spiderling | | unhatched\_spiderlingX | the eggs that did not hatch from the Xth egg sac | in this table, "X" means the number of egg sac = 1, 2, 3, …15. Note: When the cell contains "#N/A", it means that no data is available. For example, in Sheet 1, F7 cell shows "#N/A", and this means that this individual did not die until the end of the experiment. In Sheet 2, D11 also contains "#N/A", and this means that this female spider did not produce the first egg sac. ## Code/software All analyses were carried out using R 4.1.3 (R Core Team, 2023). The packages were described in the file. We tested the effect of copulation duration treatments on several response variables associated with female reproductive success. These variables included the time interval between mating and production of the first egg sac, total number of egg sacs, cumulative mass of all egg sacs, and total number of spiderlings. We used a general linear model (GLM) to investigate the effect of copulation interruption treatment (factor with 6 levels) on the various response variables. If the effect of copulation interruption was significant, Tukey post-hoc tests were conducted to reveal differences between means. As assumptions of normality and homoscedasticity were violated for time lapse until first egg sac production, the nonparametric Kruskal Wallice test was used followed by Wilcoxon signed-rank tests for pair-wise comparisons (with a Benjamini-Hochberg procedure to correct for inflated type I errors).