Epistatic interactions between sex chromosomes and autosomes can affect the stability of sex determination systems

Sex determination (SD) is an essential and ancient developmental process, but the genetic systems that regulate this process are surprisingly variable. Why SD mechanisms vary so much is a longstanding question in evolutionary biology. SD genes are generally located on sex chromosomes which also carry genes that interact epistatically with autosomes to affect fitness. How this affects the evolutionary stability of SD mechanisms is still unknown. Here, we explore how epistatic interactions between a sexually antagonistic (SA) non-SD gene, located on either an ancestral or novel sex chromosome, and an autosomal gene affect the conditions under which an evolutionary transition to a new SD system occurs. We find that when the SD gene is linked to an ancestral sex chromosomal gene which engages in epistatic interactions, epistasis enhances the stability of the sex chromosomes so that they are retained under conditions where transitions would otherwise occur. This occurs both when weaker fitne...

性别决定（Sex determination, SD）是一类基础且古老的发育过程，但其调控的遗传系统却呈现出惊人的多样性。为何性别决定机制会产生如此显著的差异，是进化生物学领域长期存在的未解难题。性别决定基因通常定位于性染色体上，而性染色体同时携带着可与常染色体发生上位性互作（epistatic interactions）并影响个体适合度的基因。这类互作对性别决定机制进化稳定性的影响目前仍未明确。本研究探讨了位于祖先性染色体或新生性染色体上的性拮抗（Sexually antagonistic, SA）非性别决定基因，与常染色体基因之间的上位性互作，如何影响向新型性别决定系统进化转变的发生条件。研究发现，当性别决定基因与发生上位性互作的祖先性染色体基因连锁时，上位性作用会增强性染色体的稳定性，使得性染色体在原本会触发进化转变的条件下得以保留。该现象在较弱适合度……