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Females more resistant to lovemaking unless 'wined and dined' first, insect study shows
When it comes to the insect world, males who expect sex without first offering their partner a tasty meal are likely to get a good kicking from angry females, says a Sussex evolutionary biologist involved in a new study.
Males providing gifts of food to females during courtship or mating is common in the insect world but entomologists have debated why this practice has evolved. The two main theories are that the male is using food to distract the female, so he can mate for longer, or that he is trying to ensure she is better fed, to ensure stronger offspring.
To answer this question, Sussex’s Dr James Gilbert worked with Professor Karim Vahed at the University of Derby and researchers at the Department of Entomology at the California Academy of Sciences and the Instituto Tecnológico de Ciudad Victoria in Mexico to look at the mating habits of bushcrickets, or katydids.
The results of the joint study to be published in the online edition of the journal Evolution on Wednesday May 21 showed that, in most cases, male bushcrickets do give food gifts, but there are some species in which the practice has been dropped.
They reveal that – when it comes to bushcrickets – males’ gifts have far more to do with prolonging sperm transfer than any more ‘considerate’ thoughts about ensuring a good start in life for their children. Looking at what these males do instead, can help to tell us about the original reason behind the gift itself.
The researchers looked at 44 bushcricket species. In most, the male produces a food gift of a large blob of jelly (the spermatophylax), which can weigh as much as a third of his own bodyweight.
In a minority of species, male bushcrickets produce little or no food, but instead have evolved a far less pleasant practice. To keep the female attached, males use many bizarre kinds of clasping devices near their genitals that can resemble gin trap teeth, spikes that puncture the female’s abdomen, and even ‘handcuffs’ that completely encircle her.
Unsurprisingly, female bushcrickets in those species with prolonged copulation and reduced or absent gifts resist by kicking and biting the males, and shifting around to throw them off.
Males who do present females with a spermatophylax don’t receive this kind of resistant behaviour from their partners.
The paper’s lead author Dr Vahed says: “Such conflict shows that males who don’t give gifts are trying to ensure they transfer as much sperm into the female as possible (and often more than she wants). We see this forceful approach by males in all bushcricket species where nuptial gifts have been lost.”
Dr Gilbert adds: “If these ‘bear traps’, ‘spikes’ and ‘handcuffs’ have evolved to prolong sperm transfer in bushcrickets which have lost nuptial gifts, it’s likely that the nuptial gift serves the same purpose in those species that still use it.”
The researchers concluded that both of the male approaches to mating – whether using food or force – were about maximising the number of offspring they produce rather than any concerns about ensuring a good start for their children.
The full version of the latest study – entitled Functional equivalence of grasping cerci and nuptial food gifts in promoting ejaculate transfer in katydids will be published online in the journal Evolution on May 21. A shorter online version is now available at web link http://onlinelibrary.wiley.com/doi/10.1111/evo.12421/abstract