Data from: Misregulation of spermatogenesis genes in Drosophila hybrids is lineage-specific and driven by the combined effects of sterility and fast male regulatory divergence.

Hybrid male sterility is a common outcome of crosses between different species. Gene expression studies have found that a number of spermatogenesis genes are differentially expressed in sterile hybrid males, compared with parental species. Late-stage sperm development genes are particularly likely to be misexpressed, with fewer early-stage genes affected. Thus, a link has been posited between misexpression and sterility. A more recent alternative explanation for hybrid gene misexpression has been that it is independent of sterility and driven by divergent evolution of male-specific regulatory elements between species (faster male hypothesis). The faster male hypothesis predicts that misregulation of spermatogenesis genes should be independent of sterility and approximately the same in both hybrids, whereas sterility should only affect gene expression in sterile hybrids. To test the faster male hypothesis vs. the effect of sterility on gene misexpression, we analyse spermatogenesis gene expression in different species pairs of the Drosophila phylogeny, where hybrid male sterility occurs in only one direction of the interspecies cross (i.e. unidirectional sterility). We find significant differences among genes in misexpression with effects that are lineage-specific and caused by sterility or fast male regulatory divergence.

杂种雄性不育（hybrid male sterility）是不同物种间杂交的常见结果。基因表达研究显示，相较于亲本物种，不育杂种雄性体内的大量精子发生（spermatogenesis）基因存在差异表达。其中，精子发生晚期的发育基因尤其容易出现表达异常，受影响的早期阶段基因则相对较少。因此，学界已提出表达异常与不育之间存在关联的假说。而针对杂种基因表达异常的一种较新的替代性解释则认为，该现象与不育无关，而是由物种间雄性特异性调控元件（male-specific regulatory element）的趋异进化所驱动，即雄性进化更快假说（faster male hypothesis）。该假说预测，精子发生基因的调控异常应独立于不育，且在两类杂种中表现大致相同；而不育仅会在不育杂种中影响基因表达。为验证雄性进化更快假说与不育对基因表达异常的影响，我们分析了果蝇（Drosophila）系统发育中不同物种对的精子发生基因表达情况——这类物种对的种间杂交仅在单方向上会产生杂种雄性不育，即单向不育（unidirectional sterility）。本研究发现，不同基因的表达异常存在显著差异，其效应具有谱系特异性，且分别由不育或雄性调控元件快速趋异进化所导致。