Sex wars: a female genital spine forces male damselflies to shorten copulation duration

Abstract

In some species males use weapons to harm females, increasing their short-term fitness. Here we show that females can use genital adaptations against males. Females of the damselfly Enallagma cyathigerum have a conspicuous vulvar spine on the 8 th abdominal segment, which contacts with the male during copulation. We tested three hypotheses for its function: it (i) inflicts damage to the male during copulation; (ii) facilitates endophytic oviposition; (iii) stimulates males during copulation to increase their investment. We found that males mated on average for 54 min with control females, but increased copulation to 99 min with females without spine. There was no evidence of physical harm of the spine on the male’s seminal vesicle, which shows 8-18 folds, exactly where the spine contacts during copulation. Females with and without spine exhibited the same egg-laying rates and showed similar fecundity and fertility. Longevity was also similar in males mated to control and spineless females. In contrast to many species where females resist male harassment by behavioral responses, the morphological adaptation observed in E. cyathigerum appears to act as a sexual weapon, allowing females to control copulation duration. We suggest that the spine has evolved because of sexual conflict over mating duration.

A red flag: an experimental analysis of the function of pink colouration in males of Calopteryx haemorrhoidalis asturica (Odonata: Calopterygidae)

“…Although damselflies are ectothermic animals, we found no effect of air temperature on mating duration, nor an effect of time of day on the whole copulation, but a positive effect on stage I duration ( figure 3 a ). In species with very long copulations, like those of the genera Ischnura , Enallagma or Ceriagrion , mating has a guarding function, and therefore time of day has a negative effect on copulation duration [ 36 , 39 , 40 ], but in Calopteryx , copulation is brief and has no guarding function. The increase in stage I duration, which is used to remove rivals’ sperm from the female genitalia [ 35 ], could be explained if over the day females were more likely to be mated, and therefore males might need more time for sperm removal.…”

Behavioural Indicators of Pain and Suffering in Arthropods and Might Pain Bite Back?

“…For example, males might evolve genitals that damage the reproductive tract of females, possibly to dissuade the females from mating with another male [ 82 ]. Females may also dissuade males from prolonged copulation [ 86 ]. Further, animals engage in fights over resources, and it is possible that pain is inflicted to encourage the opponent to give up.…”

“…Sometimes the conflict between the sexes might result in female countermeasures as is seen in female damselflies, Enallagma cyathigerum , that have a conspicuous vulvar spine which contacts with the male during copulation [ 86 ]. Males copulated for longer with non-virgin females that had the spine removed, showing that the spine reduced the duration of mating and might reduce the male’s ability to remove the sperm from a previous copulation.…”

“…Males copulated for longer with non-virgin females that had the spine removed, showing that the spine reduced the duration of mating and might reduce the male’s ability to remove the sperm from a previous copulation. It was proposed that the “spine allows females to exert some control over copulation duration by producing enough “discomfort” or “pain” to males to reduce copulation duration” [ 86 ].…”