Sneak_early_dataset

In species with external fertilisation, sperm release by males is considered crucial for synchronizing with female egg release, yet little is known about sperm release strategies when females lay eggs over extended periods. In the intertidal goby Bathygobius fuscus, smaller males intrude into the nest during pair spawning, which lasts several hours, and release sperm. Here, we investigated how the timing of sneaking affects the paternity of sneaker males, using controlled aquarium experiments combined with genetic paternity analysis. Our results showed that early nest intrusion after the onset of egg-laying (within approximately 1 hour) significantly increased sneaker male paternity. This may be partly because early released sperm remain viable for several hours and can fertilise eggs laid later. Another possible mechanism is that females laid approximately 70% of their total eggs during the first hour of spawning. These findings suggest that early sneaking maximizes fertilization opportunities of sneaker males, likely as an adaptation to prolonged oviposition and long sperm longevity. This study proposes the importance of considering the timing and sequence of sperm release in understanding the consequences of sperm competition in externally fertilising species with a time gap between sperm release and fertilization, similar to that of species with internal fertilisation.