A kin-selection approach to the resolution of sex-ratio conflict between mates

We investigate an instance of conflict between mates over the sex ratio of their brood. We construct a kin-selection model for the evolution of the sex ratio assuming local resource competition (LRC) among females. We explore two basic scenarios: (a) the case where parents make simultaneous sex-ratio decisions (the simultaneous allocation model); and (b) the case where parental sex-ratio decisions occur one after the other (the sequential allocation model). In the simultaneous investment model, resolution of the conflict between mates depends on the extent to which relative paternal contribution influences the brood sex ratio. In the sequential allocation model, fathers determine primary sex-ratio through fertilization bias; then mothers modify the paternal sex-ratio decision by adjusting the level of investment of some resource that contributes to offspring survival. Under the sequential model, a compromise is always achieved; however this compromise favours one perspective or the other, depending on the extent to which maternal investment influences offspring survival.