Effect of population density on relationship between pre- and postcopulatory sexual traits: supplementary material

Sexual selection theory
states that the premating (ornaments and armaments) sexual traits should trade
off with the postmating (testes and ejaculates) sexual traits, assuming that
growing and maintaining these traits is expensive and that total reproductive
investments are limited. Male–male competition and sperm competition are
predicted to affect how males allocate their finite resources to these traits.
Here, we studied relative expenditure on pre- and postmating sexual traits
among 82 species for three mammalian orders with varying population density
using comparative phylogenetic analysis. The results showed that population density affected the sexual size dimorphism (SSD) in both Artiodactyla
and Carnivora, but not in Primates. However, relative testis mass and sperm sizewere not affected
by population density. Moreover, we did not find associations between the SSD
and testis mass or sperm size in three taxonomic groups. The interspecific
relationships between pre- and postcopulatory sexual traits did not change with
increased population density. Our findings suggest that population density did
not affect variation in relationship between pre- and postcopulatory sexual
traits for these three mammalian orders.