EVOLUTIONARILY STABLE STRATEGY SEX-RATIOS WHEN CORRELATES OF RELATEDNESS CAN BE ASSESSED

In a structured population, with partial dispersal of offspring, there will be competition among related offspring for reproductive resource s, or local resource competition (LRC), and, when the strength of this competition differs between the sexes, this will generate a sex ratio bias in favor of the sex with the least LRC. Standard models assume t hat the parent, in choosing the sex ratio, responds to the average lev el of LRC in the population. However, there will always be variation i n the relatedness of the parent to her breeding neighbors, and this wi ll affect the strength of the LRC experienced by her offspring. If she can assess this relatedness variation, or correlates thereof, it migh t be adaptive for her to respond by shifting the sex ratio bias of her offspring appropriately. We examine this question with an inclusive f itness model in a patch-structured population with partial dispersal o f mated offspring. The analysis is complicated, but an overall conclus ion is that, for moderate dispersal rates, natives should employ a mor e female-biased sex ratio than immigrants. We find that these results fit sex ratio data in a thrips Hoplothrips pedicularius population.