Abstract
BackgroundThe fertilization success in sperm competition in externally fertilizing fish depends on number and quality of sperm. The time delay between sequential ejaculations may further influence the outcome of sperm competition. Such a time interval can load the raffle over fertilization if fertilization takes place very fast. Short fertilization times are generally assumed for externally fertilizing fish such as the three-spined stickleback (Gasterosteus aculeatus). In this pair-spawning fish, territorial males often try to steal fertilizations in nests of neighbouring males. This sneaking behaviour causes sperm competition. Sneakers will only get a share of paternity when eggs are not fertilized immediately after sperm release. Contrary to males, females may be interested in multiple paternity of their clutch of eggs. There thus may be a sexual conflict over the speed of fertilization.ResultsIn this study we used two different in vitro fertilization experiments to assess how fast eggs are fertilized in sticklebacks. We show that complete fertilization takes more than 5 min which is atypically long for externally fertilizing fishes.ConclusionThis result suggests that the time difference does not imply high costs to the second stickleback male to ejaculate. Slow fertilization (and concomitant prolonged longevity of sperm) may be the result of sexual conflict in which females aimed at complete fertilization and/or multiple paternity.
Highlights
The fertilization success in sperm competition in externally fertilizing fish depends on number and quality of sperm
The reproductive success of males in teleost fish with external fertilization is often influenced by the level of sperm competition, which is assumed to be raffle-based
This study provides evidence that fertilization of an egg clutch in sticklebacks is taking minutes rather than seconds (Fig. 1). This is exceptional if compared to fertilization durations of other teleost fishes [13,14] and contradicts the general assumption that fertilization is very fast in teleost fishes [4,9,10]
Summary
The fertilization success in sperm competition in externally fertilizing fish depends on number and quality of sperm. The reproductive success of males in teleost fish with external fertilization is often influenced by the level of sperm competition, which is assumed to be raffle-based. Successful reproduction depends on a male's ability to access and defend a female, on the proportion of a male's sperm in a possible competition [1,2,3], and on ejaculate characteristics of competing males [4]. The latter includes (page number not for citation purposes)
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