To investigate constraints imposed by male parental behavior on male mating success we compared mate competition in two related 'species' of stickleback, one showing parental care (threespine stickleback, Gasterosteus aculeatus), the other not (white stickleback, Gasterosteus sp.). Three males of each species (tested separately) competed for spawnings with gravid females over a 10-day period. Our findings showed that once a threespine male acquires its first clutch of eggs, the chances of it spawning successively over the next 4 days increase, after which courtship activity declines and parental care of eggs increases. This leads to a serial pattern of spawning amongst the three males in which the second male spawns successively in its nest after the first male has completed its spawnings, followed by the third male, if it spawns at all. However, the third male is more likely to steal fertilizations in the nests of the other two males; stolen fertilizations represented an estimated 29% of the spawning frequency of the third male, compared with 5 and 0% for the second and first males, respectively. The order in which threespine males spawned was correlated with the order in which they initiated nest construction and their ability to defend and maintain a nest site. Immediately after spawning, white stickleback males disperse their eggs among clumps of filamentous algae, where the eggs develop without further parental assistance. In contrast to threespines, white sticklebacks tested under the same competitive conditions showed a random pattern of spawning amongst the three males and stolen fertilizations were not observed. This difference in spawning pattern presumably reflects the time constraint imposed on the sexual phase by the imminent need for parental care once a threespine male obtains eggs. Without the need for parental care of eggs, white males that spawn are not under the same time constraints and therefore each successive spawning is of equal value among competing males, resulting in a random pattern of spawning. In contrast, an asymmetry exists in threespines in which males with freshly spawned eggs in their nest increase their courtship intensity relative to males without eggs, resulting in a serial or ordered pattern of spawning among the males. It is further suggested that stolen fertilizations may be a secondary adaptation to offset any inability to compete effectively for nest sites and females during the initial part of the breeding period.
Sexual selection favours male parental care, when females can choose
