Traumatic mating increases anchorage of mating male and reduces female remating duration and fecundity in a scorpionfly species

Traumatic mating is the male wounding his mate during mating using
specialized anatomy. However, why males have evolved to injure their mates
during mating remains poorly understood. We studied the traumatic mating
and copulatory wounding of the mate’s genitalia by the male in the
scorpionfly Dicerapanorpa magna to determine its effects on male and
female fitness. The results showed that the sharp teeth on the male
gonostyli penetrate the female genitalia and cause copulatory wounds, and
the size of the area of the wounds on the female genitals is positively
related to the number of times females mated. When the injurious teeth
were encased with low-temperature wax, preventing their penetration of the
female’s genitalia during mating, male mating success and copulation
duration were reduced significantly, indicating the importance of the
teeth in allowing the male to secure copulation, remain in copula and
effectively inseminate his mate. The remating experiments showed that the
traumatic mating had little effect on the female mating refractory period
(time between matings), but significantly reduced the female remating
duration with subsequent males. The reduction of the female remating
duration likely benefits the first-mating male as he has a longer
copulation duration, and thereby transfers more sperm into the female’s
spermatheca. The copulatory wounds reduced female fecundity, but did not
accelerate the timing of egg deposition by the female. This is likely the
first report that traumatic mating can reduce the female remating duration
through successive remating experiments in animals. Overall, our results
provide evidence that traumatic mating in the scorpionfly helps increase
the male’s anchoring control during mating and provides him advantage in
sperm competition, but at the expense in lowering female fecundity.