Facultative decrease in mating resistance in hermaphroditic Caenorhabditis elegans with self-sperm depletion

Facultative change in mating decisions can result from both exogenous and endogenous factors. The hermaphroditic roundworm, Caenorhabditis elegans, is a model system for many areas of biology, yet, aspects of its reproductive biology are not well understood. Here, we present data suggesting that the reproductive behaviour of hermaphrodites changes with self-sperm status. Self-sperm containing hermaphrodites are more likely to eject male ejaculate after insemination than self-sperm depleted hermaphrodites, presumably reducing the likelihood of fertilization by male sperm. Self-sperm depleted hermaphrodites are more likely to mate, and mate in a shorter period of time than self-sperm containing hermaphrodites. This increase in the willingness to mate is correlated with self-sperm depletion, but not hermaphrodite age. Hermaphrodites that have exhausted their self-sperm also show a lower rate of sprinting away from males than self-sperm containing hermaphrodites, indicating a lower level of mating resistance. The combined results suggest that self-sperm containing hermaphrodites are more likely to show precopulatory mate avoidance as well as postcopulatory mechanisms to avoid fertilization by males than sperm-depleted hermaphrodites, presumably to delay outcrossing until self-sperm is exhausted. Thus, there appears to be a shift in hermaphrodite mating behaviour based on reproductive status.