Sexually antagonistic chromosomal cuckoos

Abstract

The two kinds of sex chromosomes in the heterogametic parent are transmitted to offspring with different sexes, causing opposite-sex siblings to be completely unrelated for genes located on these chromosomes. Just as the nest-parasitic cuckoo chick is selected to harm its unrelated nest-mates in order to garner more shared resources, sibling competition causes the sex chromosomes to be selected to harm siblings that do not carry them. Here we quantify and contrast this selection on the X and Y, or Z and W, sex chromosomes. We also develop a hypothesis for how this selection can contribute to the decay of the non-recombining sex chromosome.

Figure 1

The constraints on the accumulation of new mutations that are Y-linked and harm sisters, X-linked and harm brothers or autosomal and harm one sex of sibling. Y-linked mutations accumulate over the entire parameter space, X and autosomal mutations only when they map below the curves. Black curves denote X-linkage, grey curves autosomal linkage; solid curves are based on Hamilton's rule and dashed curves are based on a population genetic model.

Figure 2

Coevolution between selfish Y chromosomes that code for harmful sibling–sibling interactions that harm sisters, and the X and autosomes that are selected to silence them.