Long-Term Sperm Storage in a Superfetatious Live-Bearing Fish (Poeciliopsis gracilis, Poeciliidae)

Abstract

Sperm storage is a post-copulatory strategy by which females can improve their fecundity by creating asynchrony between mating and fertilization. Sperm storage duration varies across vertebrate species, wherein longer sperm storage is thought to coincide with better reproductive success. Among the vertebrates, live-bearing fishes of the family Poeciliidae are generally assumed to store sperm for extended periods of time, but the temporal dynamics of this process remain unknown for most species. To date, research suggests that superfetatious poeciliids-which give birth to more frequent, temporally overlapping broods-may be able to store sperm longer than non-superfetatious species. However, robust empirical data for superfetatious poeciliids is very limited. Here, we assess the maximum duration of sperm storage and usage in the superfetatious poeciliid Poeciliopsis gracilis by comparing offspring production over time for both sexually isolated (single) and paired fish. We found that (a) the majority of P. gracilis females can store sperm for a maximum of 5 months with a smaller fraction of individuals able to extend this period to nearly 7 months, likely by "skipping broods," and (b) the number of offspring produced decreases over time post-isolation. With this study, we expand our knowledge of post-copulatory strategies by providing an assessment of both sperm storage longevity and its impact on offspring production over time in a superfetatious, live-bearing fish from the family Poeciliidae. We aim to encourage further research to generate and publish data on sperm storage longevity across the family Poeciliidae to elucidate how sperm storage varies across species with different reproductive strategies.

Keywords: Poeciliidae; Poeciliopsis gracilis; sperm longevity; sperm retention; viviparity.

FIGURE 1

A representative photograph of a Poeciliopsis gracilis female. Photo credit: J. L. van Leeuwen.

FIGURE 2

Offspring per brood over time: (a) A scatter‐plot of the number of offspring produced for both paired and single fish over time in days post‐isolation (dpi). Offspring production was not recorded for the first 78 (for cohorts 1 and 3) or 134 (for cohort 2) days post‐isolation. Fitting lines for each group include 95% confidence intervals shown by the transparent ribbons. (b) The number of offspring over time, in binned days post‐isolation, for paired and single fish in all cohorts combined as predicted by our ZINB model. Lines indicate the model predictions of the effect of the interaction variable (status [single/paired] × time post‐isolation [binned days]), with the lower and upper bounds of the 95% confidence interval shown by the transparent ribbons. Points on the graph show the actual number of offspring per fish in each bin used to generate the model.

FIGURE 3

Time between broods (i.e., interbrood interval) over time: (a) A scatter plot of the number of days between broods over time in days post‐isolation (dpi) for paired and single fish. Offspring production, and hence interbrood interval, was not recorded for the first 78 (cohorts 1 and 3) or 134 (cohort 2) days post‐isolation. Fitting lines for each group include 95% confidence intervals shown by the transparent ribbons. (b) The time between broods in binned days post‐isolation, for paired and single fish as predicted by our GLM model. Lines indicate the model predictions of the effect of the interaction variable (status [single/paired] × time post‐isolation [binned days]), with the lower and upper bounds of the 95% confidence interval shown by the transparent ribbons. Points on the graph show the actual time in days between broods per fish in each bin used to generate the model. (c) The number of days between broods for paired and single fish for both their first and last brood intervals. Individual points show the number of days between broods per fish used to generate the violins. Large points with horizontal lines indicate the mean per group.