After controlling for confounding factors such as evolutionary history, an increase in average body size makes the difference in body size larger if the species has larger males, and smaller if it has larger females.[2] Some studies propose that this is due to sexual bimaturism, which causes male traits to diverge faster and develop for a longer period of time.[3] The correlation between sexual size dimorphism and body size is hypothesized to be a result of an increase in male-male competition in larger species,[4] a result of limited environmental resources, fuelling aggression between males over access to breeding territories[5] and mating partners.[2]
This rule has rarely been tested on parasites. A 2019 study showed that ectoparasitic philopterid and menoponid lice comply with it, while ricinid lice exhibit a reversed pattern.[7]
References
^Rensch, B. (1950). "Die Abhängigkeit der relativen Sexualdifferenz von der Körpergrösse". Bonner Zoologische Beiträge. 1: 58–69.
