LONDON, Feb. 6 (UPI) -- British scientists say a high number of male-killing bacteria among some insect species can increase female promiscuity and lead to male fatigue.
Study leader Sylvain Charlat of University College London says in some populations of tropical butterfly, the entire mating system is determined by a group of bacteria known as Wolbachia.
"Male-killing bacteria are found in many insect species including the British ladybird. We wanted to know what the effect of the bacteria is on the mating system ...," she said.
"Contrary to expectation, we also find female promiscuity actually rises when male numbers are reduced. Greater numbers of female partners leads to fatigue in males," Charlat added. "They start producing smaller sperm packages. Unfortunately, the female butterflies instinctively know that the packages are smaller and that their chances of having been impregnated after mating are lower than usual. This just makes them more rampant!"
The male-killing bacterium, transmitted from mother to son, kills the son before the embryo hatches into a caterpillar. Only female offspring of female carriers can survive, which can lead to the male population being as low as one male to every hundred females.
The study is detailed in the journal Current Biology.
