Strategic allocation of ejaculates by male Adelie penguins

Sperm competition theory suggests that males should strategically allocate sperm to those females that will bring them the Lest possible genetic retur ns. Although males of a number of species of insects and fishes have been s hown to allocate sperm strategically, we provide, to our knowledge, the fir st evidence that an avian species is also capable of allocating ejaculates. Male Adelie penguins (Pygoscelis adeliae) are more likely to transfer sper m during extra-pair copulations (EPCs) than during pair copulations. with i nvestigated the question of how males allocate ejaculates within the constr aints of limited sperm ability and found (i) that males that engaged in EPC attempts ejaculated less often when copulating with their social partner t han males that made no EPC attempts, and (ii) that there was no difference between males that were involved in failed EPC attempts and those that were involved in successful EPCs in the proportion of copulations that resulted in sperm transfer. These results indicate that males achieve strategic all ocation of sperm within the constraints of limited sperm availability by wi thholding ejaculates from their social partners.