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。被Cardinium诱导细胞质不相容（cytoplasmic incompatibility, CI）的寄生蜂（parasitoid wasp）Encarsia suzannae（以下简称iES），以及未被细菌内共生体（bacterial endosymbionts）感染的姊妹种E. gennaroi（以下简称EG），其分化可能源于CI与不对称杂交不相容（asymmetric hybrid incompatibilities）的协同作用。尽管目前因F1杂交子代（F1 hybrid progeny）不育，合子后隔离（postzygotic isolation）已完全形成，但合子前隔离仍处于初始阶段。我们设置了实验室种群笼实验，以评估iES与EG的两种配对组合间的互作结局：其一为iES与EG的直接配对，其二为经抗生素清除Cardinium的处理组iES（cured ES, cES）与EG的配对。我们还构建了理论模型（theoretical model），旨在探究生活史差异（life history differences）与不对称交配（asymmetric mating）在竞争结局（competitive outcomes）中的作用。各处理组的4个种群笼中，有3个均以iES占据竞争主导地位。我们发现了由不对称交配偏好（asymmetric mating preferences）驱动的生殖干扰（reproductive interference）证据，这为iES带来了竞争优势——该物种能更有效地识别异种个体。然而，我们并未发现此前研究中报道的、与iES体内Cardinium感染相关的繁殖力成本（fecundity cost）。该理论模型在很大程度上验证了实验结果。种群笼实验中仅观测到iES对EG的微弱竞争优势，这表明在更为复杂的异质环境（heterogeneous environment）中，二者或可实现共存。这一推论得到了野外同域分布（sympatry）证据的支持：初步数据显示，同域分布区域内的生殖特征置换（reproductive character displacement）可能强化了合子后隔离。