Behavioural observations (frequency and timing of copulation attempts) and paternity analysis from blood samples to investigate sperm competition of adelie penguins (Pygoscelis adeliae)

Sexual selection theory suggests that males compete for females and females choose males. Sperm competition is one aspect of this competition. There are two possible mechanisms of sperm competition, either the last male to copulate with the female prior to fertilisation gains paternity or the male copulating most often with the female gains paternity. This study's aim was to investigate sperm choice and the mechanisms of sperm competition in the adelie penguin with a combination of behavioural observations and paternity analysis to give insight into female behaviour, patterns of sperm precedence and the mechanism of sperm competition.

All penguin pairs in a colony at Cape Bird were individually tagged and measurements of body size was recorded. Ecstatic call displays were recorded from males and body size measurements were taken at the time of display and again 3 weeks later to determine body mass changes associated with fasting to determine if there are characteristics of males calls that may be used by the females to indicate the size and/or condition of males in relation to their ability to be able to withstand the period of fasting necessary for the first incubation spell. Females were observed througout the pre-laying period for frequency and timing of copulations.

For each copulation attempt the identity of the male and female, the site at which the activity took place and the outcome of each attempt (if sperm transfer was successful or the reason for failure) was recorded. Sperm samples were collected to assess levels of sperm transfer and male fertility by pressing a microscope slide to the females cloaca after copulation and viewing 30 fields of view and classifying the sperm as either a) abundant, b) traces present or c) absent. Measurements of body size from initial and final male pairs was compared to determine female selection traits. The timing between ejaculates (successful to the next successful and successful to the next unsuccessful) was compared in male penguins to examine whether semen is a limiting resource and to assess the potentially important consequences of semen depletion for sperm competition and paternity assurance. Female extra pair copulations in exchange for food or resources ("penguin prostitution") was observed and reported. Blood samples were taken from penguin pairs during tagging and from chicks after hatching for paternity analysis. Blood smears were also analysed to assess whether females switch from parasitised to unparasitised males.