Tie that binds - Hill-Robertson Interference can produce signals of sexual antagonism even in the absence of sexually antagonistic selection

Abstract

1Sexually antagonistic (SA) selection on a trait with a shared genetic basis between the sexes is thought to lead to Intralocus Sexual Conflict (IaSC). A common way of measuring IaSC involves characterising the joint distribution of breeding values of male and female fitness using the intersexual additive genetic correlation for fitness (rmf,W). However, there is considerable variation in the empirical estimates of rmf,W - with estimates ranging from significantly negative (suggestive of strong IaSC) to significantly positive (suggesting an absence of IaSC) - even among closely related populations of the same species. Here, we investigate whether SA selection is even necessary for rmf,W to be negative. We first highlight that the sign of rmf,W depends on a term that describes direct sex-specific selection, and another that describes indirect selection mediated by linkage disequilibria (LD). We show that rmf,W can be negative if (1) selection is perfectly sex-limited - such that every locus affects the fitness of one sex only - and (2) the LD between closely-linked male-beneficial and female-beneficial alleles is on average negative as predicted under Hill-Robertson Interference (HRI). We test this idea using individual-based simulations. Our results suggest that populations evolving under purely sex-limited selection exhibit a prominent negative bias in rmf,W that gets strengthened by a reduction in the recombination rate. Therefore, HRI can drive rmf,W to be negative even in the absence of SA selection suggesting that negative estimates of rmf,W should not automatically be considered as evidence of IaSC.