Data from: Oviposition traits generate extrinsic postzygotic isolation between two pine sawfly species

Background: Although empirical data indicate that ecological speciation is prevalent in nature, the relative importance of different forms of reproductive isolation and the traits generating reproductive isolation remain unclear. To address these questions, we examined a pair of ecologically divergent pine-sawfly species: while Neodiprion pinetum specializes on a thin-needled pine (Pinus strobus), N. lecontei utilizes thicker-needled pines. We hypothesized that extrinsic postzygotic isolation is generated by oviposition traits. To test this hypothesis, we assayed ovipositor morphology, oviposition behavior, and host-dependent oviposition success in both species and in F1 and backcross females.
Results: Compared to N. lecontei, N. pinetum females preferred P. strobus more strongly, had smaller ovipositors, and laid fewer eggs per needle. Additionally, we observed host- and trait-dependent reductions in oviposition success in F1 and backcross females. Hybrid females that had pinetum-like host preference (P. strobus) and lecontei-like oviposition traits (morphology and egg pattern) fared especially poorly.
Conclusions: Together, these data indicate that maladaptive combinations of oviposition traits in hybrids contribute to extrinsic postzygotic isolation between N. lecontei and N. pinetum, suggesting that oviposition traits may be an important driver of divergence in phytophagous insects.

研究背景：尽管实证数据表明生态物种形成（ecological speciation）在自然界中普遍存在，但不同形式生殖隔离的相对重要性，以及介导生殖隔离的相关性状仍未明确。为解答这一科学问题，我们针对一对生态分化的松叶蜂物种开展研究：新松叶蜂（Neodiprion pinetum）专性取食针叶较薄的北美白松（Pinus strobus），而莱氏新松叶蜂（N. lecontei）则以针叶较厚的松树类群为寄主。我们提出假说：外在后合子隔离（extrinsic postzygotic isolation）由产卵相关性状所介导。为验证该假说，我们测定了两个物种及其F1代、回交（backcross）世代雌蜂的产卵器形态、产卵行为以及寄主依赖型产卵成功率。
研究结果：相较于莱氏新松叶蜂，新松叶蜂雌蜂对北美白松的偏好性更强，产卵器更小，且单针叶产卵量更少。此外，我们观测到F1代与回交雌蜂的产卵成功率会随寄主类型及性状组合出现下降。其中，兼具新松叶蜂型寄主偏好（偏好北美白松）与莱氏新松叶蜂型产卵性状（产卵器形态与产卵模式）的杂交雌蜂，其产卵表现尤为不佳。
研究结论：综合上述实验数据，杂交个体中产卵相关性状的适应不良组合，促成了莱氏新松叶蜂与新松叶蜂之间的外在后合子隔离，这一结果暗示产卵相关性状可能是植食性昆虫（phytophagous insects）物种分化的重要驱动因子。