Polygyny in the Era of Molecular Biology: Revisiting Bartholomew’s Model

The theory of sexual selection hypothesizes that, when females are selected to perform most parental investment, males compete for access to mates and polygyny evolves. Polygyny should result in high variance in male reproductive success, with a few males fathering a disproportionate number of pups. I tested this prediction by reviewing the literature on paternity, available for seven otariids. I identified a total of eight publications with data on paternity in seven species at 12 colonies. Overall, harem size produced an estimated mean of 20.7 pups per dominant male (assuming that the male fathered all pups born within its harem), but genetic analysis revealed that territorial males fathered 32.5% of pups born in colonies, resulting in an estimated two pups per territorial male, i.e. behavioural estimations of reproductive success was tenfold (20/2) higher than genetic ones; many males were unsuccessful in obtaining mates, even when following the dominant strategy; size of harem did correlate with paternity by territorial males but the slope was significantly lower than expected from behavioural estimations; differences in paternity between territorial and satellites males were not statistically significant in most studies. Generalizations of classical theories on the evolution of polygyny may need qualification in the light of evidence provided by molecular ecology.