Sexual conflict in mites (Sci Rep paper)

Scientific Reports just published my latest paper on bulb mites! The article describes a surprising result when I investigated the fecundity of female mites from colonies that had gone through artificial selection for larger fighting legs (a trait that only males of the fighter morph present). Basically these lines were selected for either larger legs or smaller legs in the fighters. Females and males of the other morph (scramblers) do not fight, so they have no benefit of having their legs enlarged, but in 2018 I showed that their leg sizes coevolved with that of fighters (published here in Proc B). Then I decided to investigate the costs females paid for these coevolved larger legs.

I expected that females from the up lines (who coevolved larger legs) would pay a cost for having these (perhaps useless) larger legs. It would be a classic case of sexual conflict, but elegantly demonstrated via artificial selection and coevolution. However, to my absolute surprise, females from these up lines evolved higher fecundity, rather than lower fecundity, compared to females from the down lines.

Sexual conflict theory predicted the opposite! I had no reason to expect this result — I just wanted to quantify the damage sexual conflict could be doing here. So what happened? I believe maybe by selecting on a condition dependent trait (these legs show condition dependence in the morph level, where larger males become fighters) I perhaps "accidentally" selected on other genes that elevate condition in the up lines, explaining the higher fecundity of females in such lines. This is of course just an ad-hoc hypothesis, so if you have a better explanation please get in touch with me as I would love to discuss!

It is hard to describe how much work goes into an experiment like this. My friend Huon and I worked on this artificial selection protocol for about a year and a half, and later we set up the fecundity trial and counted eggs for months — after all we counted a total of 26,731 mite eggs (they are TINY).