Onthophagus babirussa sexual size dimporphism and male sexual trait files and R codes

Sexual size dimorphism (SSD) arises when natural selection and sexual
selection act differently on males and females. Male-biased SSD is rare in
insects and usually indicates strong selection pressure on a population or
species. Patterns of SSD can also vary between populations of species that
are exposed to different environmental conditions, such as differing
resource availability and diversity. Here, we investigate intra-specific
variation in SSD as well as relative investment in precopulatory (horn
length) and postcopulatory traits (sperm length and testes weight) in a
tropical rainforest dung beetle Onthophagus babirussa across Singapore and
Peninsular Malaysia. Overall, three out of four populations displayed
significant male-biased SSD and SSD was greater in populations with
smaller overall body size. Average male body size was similar across all
populations while female body size was significantly smaller in Singapore,
suggesting that the pronounced SSD may also be due to stronger sexual
selection on male body size in Singapore populations. All populations
showed significant investment in horns as a weapon used in precopulatory
competition, while postcopulatory traits showed no clear scaling
relationship with body size, suggesting a higher priority on precopulatory
sexual traits in the mating system of this species.