The promiscuous sex lives of bush-crickets: Females prefer one night stands and avoid mating with the same male

By Karim Vahed - 7 June 2017

Our study is really about the extent to which females in nature mate with the same male as opposed to, maybe, lots of different males. We're still really learning about the extent to which females are polyandrous, that is mating with more than one male. Our study used the dark bush-cricket as our model organism and, using DNA analysis, we are able to actually work out for females that had mated completely naturally in the field, for each of the females matings whether that mating was with a male she'd mated with before or with a different male. And not only that but also which of the male's sperm was used to fertilise her eggs.

The species we chose to study was ideal, it was the dark bush-cricket, and we studied it in the United Kingdom. This species is very interesting because each time the female mates, a separate envelope of sperm is formed within the female's sperm storage organ and females store all of the sperm from each male she mates with throughout her life.

So what we did is we took females that had mated under completely natural field conditions down in Devon in the UK, we took them back to the lab, allowed them to lay eggs, and then at the end of their lives we dissected the females and we were able to analyse the DNA of each of these vesicles of sperm in the female sperm storage. For one thing, to work out how many different males were represented. We were also able to analyse the DNA of the eggs to work out which of the males fertilised the eggs.

Our results revealed that females are surprising promiscuous in this species. 80% of the females had actually mated with a different male on each successive mating and females mated with up to six different males.

In terms of who fertilised the eggs, it is quite interesting. The males that were the most recent matings tended to fertilise most of the eggs and also males that had transferred bigger ejaculates in the first place. But the really important finding is that females seem to, actually, almost be actively avoiding mating with the same male. The extent to which females are polyandrous as opposed to re-mating with the same male actually backs up previous laboratory studies that have suggested that, in crickets at least, females actively avoid mating with males they've already mated with. Why should they do this? Well, it seems that there are all sorts of benefits to females of having genetic diversity in their offspring and also potentially being able to mate with a more genetically compatible male, so mating with more males is basically good for female fitness in these insects.