Sperm Transfer in the Adélie Penguin

Abstract

Sperm competition theory suggests that for a female that copulates with more than one male, the relative numbers of sperm inseminated will be important in determining which male fathers her offspring. Many studies of birds have reported insemination frequencies based on observations of apparent cloacal contact between male and female. Here we question whether cloacal contact is a reliable indicator of sperm transfer. This question has already been addressed in a small number of studies of captive species (Domestic fowl, Gallus domesticus: Penquite et al. 1930; Zebra Finch, Taeniopygia guttata: Birkhead et al. 1989; Bengalese Finch, Lonchura striata: Birkhead 1991). However Birkhead et al. (1988a) found differences in copulation behavior between wild and captive Zebra Finches, with wild birds copulating at a higher frequency than captive ones. So, although it has been shown for the above captive species that not all behaviorally successful copulations result in sperm transfer, it has yet to be shown for any wild species. Further, in these studies of captive species it was not determined whether sperm transfer failed as a result of the male's failure to ejaculate or absence of sperm in a successfully transferred ejaculate. Here we look at sperm transfer in a wild population of Ad6lie Penguins (Pygoscelis adeliae) by combining behavioral observations of cloacal contact and ejaculate transfer with collection of ejaculates and identification of presence or absence of sperm by microscopic examination. The aim of the study is to determine the true success rate, in terms of sperm transfer, of behaviorally successful copulations and the reason for failure of sperm transfer.