Data from: Wolbachia and host intrinsic reproductive barriers contribute additively to post-mating isolation in spider mites

Wolbachia are maternally-inherited bacteria that induce cytoplasmic
incompatibility in many arthropod species. However, the ubiquity of this
isolation mechanism for host speciation processes remains elusive, as only
few studies have examined Wolbachia-induced incompatibilities when host
populations are not genetically compatible. Here, we used three
populations of two genetically differentiated colour forms of the
haplodiploid spider mite Tetranychus urticae to dissect the interaction
between Wolbachia-induced and host-associated incompatibilities, and their
relative contribution to post-mating isolation. We found that these two
sources of incompatibility act through different mechanisms in an additive
fashion. Host-associated incompatibility contributes 1.5 times more than
Wolbachia-induced incompatibility in reducing hybrid production, the
former through an overproduction of haploid sons at the expense of diploid
daugters (ca. 75% decrease) and the latter by increasing the embryonic
mortality of daughters (by ca. 49%). Furthermore, regardless of cross
direction, we observed near-complete F1 hybrid sterility and complete F2
hybrid breakdown between populations of the two forms, but Wolbachia did
not contribute to this outcome. We thus show mechanistic independence and
an additive nature of host-intrinsic and Wolbachia-induced sources of
isolation. Wolbachia may contribute to reproductive isolation in this
system, thereby potentially affecting host differentiation and
distribution in the field.

沃尔巴克氏体（Wolbachia）是一类母系遗传的细菌，可在多种节肢动物物种中诱导细胞质不相容（cytoplasmic incompatibility）。然而，该隔离机制在宿主物种形成过程中的普遍性仍不明确，因为仅有少数研究在宿主种群不存在遗传相容性的前提下，探究了沃尔巴克氏体诱导的不相容现象。本研究利用单倍二倍体叶螨二斑叶螨（Tetranychus urticae）的两个遗传分化色型的三个种群，解析了沃尔巴克氏体诱导的不相容与宿主相关不相容之间的互作关系，以及二者对交配后生殖隔离的相对贡献。研究发现，这两类不相容通过不同机制以加性方式发挥作用。宿主相关不相容在降低杂种产生方面的贡献是沃尔巴克氏体诱导不相容的1.5倍：前者通过以二倍体雌虫为代价过量产生单倍体雄虫（降幅约75%），后者则通过提高雌虫的胚胎死亡率（降幅约49%）。此外，无论交配方向如何，我们均观察到两个色型种群间的子一代（F₁）杂种近乎完全不育，且子二代（F₂）出现完全的杂种衰退，但该现象与沃尔巴克氏体无关。综上，本研究证实了宿主固有生殖隔离与沃尔巴克氏体诱导的生殖隔离在机制上相互独立且具有加性特征。沃尔巴克氏体可能在该系统中参与生殖隔离过程，从而潜在影响宿主在野外的物种分化与分布格局。