Data from: Patterns of reproductive isolation in a haplodiploid – strong postmating, prezygotic barriers among three forms of a social spider mite

In speciation research, much attention is paid to the evolution of reproductive barriers, preventing diverging groups from hybridizing back into one gene pool. The prevalent view is that reproductive barriers evolve gradually as a byproduct of genetic changes accumulated by natural selection and genetic drift in groups that are segregated spatially and/or temporally. Reproductive barriers, however, can also be reinforced by natural selection against maladaptive hybridization. These mutually compatible theories are both empirically supported by studies, analyzing relationships between intensity of reproductive isolation and genetic distance in sympatric taxa and allopatric taxa. Here, we present the – to our knowledge – first comparative study in a haplodiploid organism, the social spider mite Stigmaeopsis miscanthi, by measuring premating and postmating pre- and postzygotic components of reproductive isolation, using three recently diverged forms of the mite that partly overlap in home range. We carried out cross experiments and measured genetic distances (mtDNA and nDNA) among parapatric and allopatric populations of the three forms. Our results show that the three forms are reproductively isolated, despite the absence of premating barriers, and that the postmating, prezygotic component contributes most to reproductive isolation. As expected, the strength of postmating reproductive barriers positively correlated with genetic distance. We did not find a clear pattern of prezygotic barriers evolving faster in parapatry than in allopatry, although one form did show a trend in line with the ecological and behavioral relationships between the forms. Our study advocates the versatility of haplodiploid animals for investigating the evolution of reproductive barriers.

在物种形成研究领域，学界长期聚焦生殖隔离屏障（reproductive barriers）的演化机制——其核心功能是阻止分化类群通过杂交再次融合为单一基因库。主流理论认为，生殖隔离屏障会逐步演化形成，作为自然选择与遗传漂变所积累的遗传变异的副产物，在空间或时间上存在隔离的类群中得以产生。然而，生殖隔离屏障也可通过自然选择对不适应杂交的淘汰作用得到强化。这两套彼此兼容的理论均获得了实证研究的支持：相关研究针对同域类群（sympatric taxa）与异域类群（allopatric taxa）的生殖隔离强度与遗传距离之间的关联展开了分析。
在此，我们报告一项据我们所知的、针对单倍二倍体生物（haplodiploid organism）的首次比较研究：以社会性叶螨（Stigmaeopsis miscanthi）为研究对象，选取其三种栖息地范围部分重叠的新近分化类群，对生殖隔离的交配前、交配后合子前以及合子后组分进行量化测定。我们开展了杂交实验，并测定了这三类群的邻域种群（parapatric populations）与异域种群间的遗传距离（线粒体DNA（mtDNA）与核DNA（nDNA））。
研究结果显示，尽管不存在交配前生殖隔离组分，这三类群之间仍存在生殖隔离；其中，交配后合子前隔离组分对生殖隔离的贡献度最高。正如预期，交配后生殖隔离的强度与遗传距离呈显著正相关。尽管其中一个类群的演化趋势符合类群间的生态与行为关联，但我们并未发现邻域种群的合子前隔离相较于异域种群演化更快的明确模式。本研究论证了单倍二倍体动物在探究生殖隔离演化机制方面的研究价值与普适性。