Data from: The complexity of mating decisions in stalk-eyed flies

All too often, studies of sexual selection focus exclusively on the
responses in one sex, on single traits, typically those that are
exaggerated and strongly sexually dimorphic. They ignore a range of less
obvious traits and behavior, in both sexes, involved in the interactions
leading to mate choice. To remedy this imbalance, we analyze a textbook
example of sexual selection in the stalk-eyed fly (Diasemopsis meigenii).
We studied several traits in a novel, insightful, and efficient
experimental design, examining 2,400 male–female pairs in a “round-robin”
array, where each female was tested against multiple males and vice versa.
In D. meigenii, females exhibit strong mate preference for males with
highly exaggerated eyespan, and so we deliberately constrained variation
in male eyespan to reveal the importance of other traits. Males performing
more precopulatory behavior were more likely to attempt to mate with
females and be accepted by them. However, behavior was not a necessary
part of courtship, as it was absent from over almost half the
interactions. Males with larger reproductive organs (testes and accessory
glands) did not make more mating attempts, but there was a strong tendency
for females to accept mating attempts from such males. How females detect
differences in male reproductive organ size remains unclear. In addition,
females with larger eyespan, an indicator of size and fecundity, attracted
more mating attempts from males, but this trait did not alter female
acceptance. Genetic variation among males had a strong influence on male
mating attempts and female acceptance, both via the traits we studied and
other unmeasured attributes. These findings demonstrate the importance of
assaying multiple traits in males and females, rather than focusing solely
on prominent and exaggerated sexually dimorphic traits. The approach
allows a more complete understanding of the complex mating decisions made
by both males and females.