SPERM COMPETITION - MATING SYSTEM, NET BREEDING-SEASON, AFFECTS TESTES SIZE OF PRIMATES

1. In taxa in which several males mate with a fertile female, males ha ve larger testes relative to their body size than do males of taxa whe re only one male normally mates. However, breeding seasonality could c onfound the association: some species with breeding seasons have unusu ally large testes; seasonal breeding could concentrate fertile females in time, so making them difficult to defend and thus promoting multi- male groups. 2. Using data from 58 species of primates, and carefully accounting for phylogeny, we investigate the potential for breeding se asonality to confound the relation between testes size and mating syst em. 3. No confounding effect exists. Multi-male taxa have very signifi cantly larger testes for their body size than do single-male taxa, ind ependently of seasonality of breeding. Seasonality has no effect whats oever in our sample, although few primates have very short breeding se asons. 4. While multi-male genera are equally likely to be seasonal as non-seasonal breeders, the single-male taxa of our sample are rarely seasonal, apparently supporting the difficulty of defence hypothesis b ut the sample by no means allows a firm conclusion.