Data from: Reproductive interference and fecundity affect competitive interactions of sibling species with low mating barriers: experimental and theoretical evidence

When allopatric species with incomplete prezygotic isolation come into secondary contact, the outcome of their interaction is not easily predicted. The parasitoid wasp Encarsia suzannae (iES), infected by Cardinium inducing cytoplasmic incompatibility (CI), and its sibling species E. gennaroi (EG), not infected by bacterial endosymbionts, may have diverged because of the complementary action of CI and asymmetric hybrid incompatibilities. Whereas postzygotic isolation is now complete due to sterility of F1 hybrid progeny, prezygotic isolation is still incipient. We set up laboratory population cage experiments to evaluate the outcome of the interaction between ES and EG in two pairwise combinations: iES vs. EG and cured ES (cES, where Cardinium was removed with antibiotics) vs. EG. We also built a theoretical model aimed at exploring the role of life history differences and asymmetric mating on competitive outcomes. In three of four cages in each treatment, ES dominated the interaction. We found evidence for reproductive interference, driven by asymmetric mating preferences, which gave a competitive edge to ES, the species that better discriminated against heterospecifics. However, we did not find the fecundity cost previously shown to be associated with Cardinium infection in iES. The model largely supported the experimental results. The finding of only a slight competitive edge of ES over EG in population cages suggests that in a more heterogeneous environment the species could coexist. This is supported by evidence that the two species coexist in sympatry, where preliminary data suggest reproductive character displacement may have reinforced postzygotic isolation.

当合子前生殖隔离（prezygotic isolation）不完全的异域物种（allopatric species）发生次生接触（secondary contact）时，二者互作的结局难以预测。本研究涉及两种寄生蜂（parasitoid wasp）：携带诱导细胞质不相容（cytoplasmic incompatibility, CI）的Cardinium卡氏菌的Encarsia suzannae（iES），以及未感染内共生菌（endosymbionts）的姊妹种（sibling species）E. gennaroi（EG），二者的物种分化可能由CI与不对称杂交不相容（asymmetric hybrid incompatibilities）的协同作用所驱动。目前二者的合子后生殖隔离（postzygotic isolation）已因F1杂交后代（F1 hybrid progeny）不育而完全建立，但合子前生殖隔离仍处于初期阶段。

我们设置了实验室种群笼实验，以评估两组两两配对组合下iES与EG的互作结局：iES 与 EG，以及清除了Cardinium的ES（cES，通过抗生素去除其体内的共生菌）与 EG。同时我们构建了理论模型，用以探究生活史差异与不对称交配对竞争结局的调控作用。

各处理组的4个种群笼中，有3个均以ES占据竞争主导地位。我们发现了由不对称交配偏好驱动的生殖干扰（reproductive interference）证据，这赋予了ES竞争优势——该物种能更精准地识别异种个体（heterospecifics）。但我们未发现此前报道的、与iES体内Cardinium感染相关的繁殖代价（fecundity cost）。

理论模型在很大程度上验证了实验结果。种群笼实验中ES仅具备微弱的竞争优势，这提示在更为异质的自然环境中，二者或可实现共存。已有证据支持这一结论：两物种在同域分布区域（sympatry）共存，初步数据显示生殖特征置换（reproductive character displacement）可能强化了二者的合子后生殖隔离。