'Bisexual' beetles are simply inept, new study finds

Date:  May 10, 2018

Source:  University of East Anglia

Same sex mating behaviour amongst male insects is much more likely to be due to incompetence, than sexual preference, male-male competition or evolutionary motivation -- according to new research from the University of East Anglia.

This type of behaviour is well-recognised, but paradoxical in the animal world. It carries all the costs of time and energy, as well as risking disease or injury, but offers no benefits towards the main function of mating -fertilisation and the propagation of genes.

Despite this, more than 100 species of insects engage in same-sex mating behaviour, and in some species the same-sex mating is more common than heterosexual mating. Why does evolution allow this seemingly wasteful behaviour to exist?

There are a number of theories about why same-sex mating persists, including gaining advantage by practising copulation -- or establishing social dominance over male rivals and reducing their fertilisation success. Other reasons might include a limited ability to recognise female mates, either because of social conditioning, or for genetic reasons.

Researchers in the School of Biological Sciences at UEA used experimental evolution to find out what might cause same sex behaviour in one particular species of insect -- the red flour beetle.

In the study, published in Animal Behaviour, results showed that within populations of mostly female beetles, the males were much more likely to copulate with other males. The researchers concluded that, where there was much less pressure to find the right mate, the beetles simply made more mistakes, because they came from an evolutionary background where mistakes are not so costly for reproductive success.

By contrast, in male-biased conditions, where there is much more intense selection on males to find the right mate in order to achieve reproductive success, same-sex matings were less frequent.

Continued