Data from: Distinct copulation positions in Drosophila pachea males with symmetric or asymmetric external genitalia

Left-right asymmetric genitalia have appeared multiple times independently
in insects and have been associated with changes in mating positions.
However, there is little experimental data on how the evolution of genital
asymmetries may have affected the evolution of mating positions or vice
versa. As opposed to its closely-related species, Drosophila pachea has a
conspicuous asymmetry in its male genitalia external lobes, with the left
lobe being 1.49 ± 0.08 (SD) times longer and thinner than the right lobe.
In a laboratory stock, we found that 20% of the males possess fully
symmetric lobes. To better understand how asymmetric genitalia may affect
mating, we compared D. pachea copulation behaviour between these mutant
males and wild-type males. We found that D. pachea wild-type males adopt a
one-sided mating posture with the male always one-sided 8.55° ± 1.79° (SD)
towards the female’s right side. Within 45-min recordings, all wild-type
males did mate whereas 39% of symmetric mutants failed to form a stable
mating complex and did not mate. In successful copulations, symmetric
mutants also adopted a right-sided mating posture but the angle between
male and female bodies was significantly more variable compared to
wild-type males. Our results suggest that lobe size asymmetry is required
for the formation of a stable mating complex and for the positioning of
the male according to a precise angle on the female. However, lobe size
asymmetry is not required for D. pachea right-sided mating posture.