Data from: Differential investment in pre- versus post-copulatory sexual selection reinforces a cross-continental reversal of sexual size dimorphism in Sepsis punctum (Diptera: Sepsidae)

Theory predicts that males have a limited amount of resources to invest in
reproduction, suggesting a trade-off between traits that enhance mate
acquisition and those enhancing fertilization success. Here we investigate
the relationship between pre- and post-copulatory investment by comparing
the mating behavior and reproductive morphology of four European and five
North American populations of the dung fly Sepsis punctum (Diptera) that
display a reversal of sexual size dimorphism (SSD). We show that the
geographic reversal in SSD between the continents (male-biased in Europe,
female-biased in North America) is accompanied by differential investment
in pre- versus post-copulatory traits. We find higher re-mating rates in
European populations, where larger males acquire more matings and
consequently have evolved relatively larger testes and steeper
hyper-allometry with body size. American populations, in sharp contrast,
display much reduced, if any, effect of body size on those traits.
Instead, North American males demonstrate an increased investment in mate
acquisition prior to copulation, with more mounting attempts and a
distinctive abdominal courtship display that is completely absent in
Europe. When controlling for body size, relative female spermathecal size
is similar on both continents, so we find no direct evidence for the
co-evolution of male and female internal reproductive morphology. By
comparing allopatric populations of the same species that apparently have
evolved different mating systems and consequently SSD, we thus indirectly
demonstrate differential investment in pre- vs. post-copulatory mechanisms
increasing reproductive success.