Wolbachia infection can bias estimates of intralocus sexual conflict

Abstract

Males and females share most of their genome and develop many of the same traits. However, each sex frequently has different optimal values for these shared traits, creating intralocus sexual conflict. This conflict has been observed in wild and laboratory populations of insects and affects important evolutionary processes such as sexual selection, the maintenance of genetic variation, and possibly even speciation. Given the broad impacts of intralocus conflict, accurately detecting and measuring it is important. A common way to detect intralocus sexual conflict is to calculate the intersexual genetic correlation for fitness, with negative values suggesting conflict. Here, we highlight a potential confounder of this measure—cytoplasmic incompatibility caused by the intracellular parasite Wolbachia. Infection with Wolbachia can generate negative intersexual genetic correlations for fitness in insects, suggestive of intralocus sexual conflict. This is because cytoplasmic incompatibility reduces the fitness of uninfected females mated to infected males, while uninfected males will not suffer reductions in fitness if they mate with infected females and may even be fitter than infected males. This can lead to strong negative intersexual genetic correlations for fitness, mimicking intralocus conflict. We illustrate this issue using simulations and then present Drosophila simulans data that show how reproductive incompatibilities caused by Wolbachia infection can generate signals of intralocus sexual conflict. Given that Wolbachia infection in insect populations is pervasive, but populations usually contain both infected and uninfected individuals providing scope for cytoplasmic incompatibility, this is an important consideration for sexual conflict research but one which, to date, has been largely underappreciated.

Natural selection reverses the exaggeration of a male sexually selected trait, which increases female fitness

“…Thus male-biased predation indirectly selects for increased female quality. predation did not alter female fitness or male sexual-trait size.Negative intersexual correlations for fitness are an indicator of intralocus sexual conflict(Bonduriansky & Chenoweth 2009) -although this can be complicated by Wolbachia infection(Duffy et al 2019) -and we find negative correlations for fitness surrogates here -mandible size determines male fitness and LRS reflects female fitness (e.g.…”

Selfish genes and sexual selection: the impact of genomic parasites on host reproduction

“…This asymmetry in fitness between the sexes can generate a strong negative intersexual genetic correlation for fitness, thus mimicking intra‐locus sexual conflict. In support of this prediction, experimental findings in D. simulans crosses coupled with simulations show that Wolbachia can generate signals of intra‐locus sexual conflict (Duffy et al , 2019). This possibility is currently largely overlooked as a potentially common source generating sexual conflict in arthropods, but is likely to be of genuine importance seeing the prevalence of CI‐inducing endosymbionts.…”

“…A negative intersexual genetic correlation for fitness is frequently interpreted as evidence for the existence of widespread intra‐locus sexual conflict where a high male fitness genotype gives rise to a low‐fitness female and vice versa . However, this negative intersexual correlation may instead be due to endosymbionts causing reproductive incompatibilities between infected males and uninfected females (Duffy et al , 2019). For example, Wolbachia (and other endosymbionts) frequently cause reproductive failure in crosses between infected males and uninfected females (CI).…”

An investigation of the sex-specific genetic architecture of fitness inDrosophila melanogaster

“…Studies have found that 𝑟 !" may be highly sensitive to the ecological context in which genetic variation is expressed (e.g., Berger Punzalan et al 2014;Duffy et al 2019). However, our estimates of 𝑟 !"…”