Data from: Mechanical and tactile incompatibilities cause reproductive isolation between two young damselfly species

External male reproductive structures have received considerable attention as a cause of reproductive isolation (RI), because the morphology of these structures often evolves rapidly between populations. This rapid evolution presents the potential for mechanical incompatibilities with heterospecific female structures during mating and could thus prevent interbreeding between nascent species. Although such mechanical incompatibilities have received little empirical support as a common cause of RI, the potential for mismatch of reproductive structures to cause RI due to incompatible species-specific tactile cues has not been tested. We tested the importance of mechanical and tactile incompatibilities in RI between Enallagma anna and E. carunculatum, two damselfly species that diverged within the past ~250,000 years and currently hybridize in a sympatric region. We quantified 19 prezygotic and postzygotic RI barriers using both naturally occurring and lab-reared damselflies. We found incomplete mechanical isolation between the two pure species and between hybrid males and pure species females. Interestingly, in species pairs for which mechanical isolation was incomplete, females showed greater resistance and refusal to mate with hybrid or heterospecific males compared to conspecific males. This observation suggests that tactile incompatibilities involving male reproductive structures can influence female mating decisions and form a strong barrier to gene flow in early stages of speciation.

雄性外生殖器作为生殖隔离（reproductive isolation, RI）的诱因已广受关注，因其形态往往在不同种群间快速演化。这种快速演化可能在交配过程中引发与异种雌性生殖结构的机械性不兼容，进而阻碍新生物种间的杂交。尽管此类机械性不兼容作为生殖隔离的普遍诱因尚未获得足够实证支持，但由物种特异性触觉信号不匹配引发的生殖结构不兼容是否会导致生殖隔离，仍未得到验证。我们针对两种豆娘——Enallagma anna与E. carunculatum——间的机械与触觉不兼容对生殖隔离的影响开展了测试；这两个物种在约25万年内发生分化，目前在同域分布区域存在杂交现象。我们利用野外自然种群与实验室饲养的豆娘个体，量化了19项合子前与合子后生殖隔离障碍。研究发现，两个纯种物种之间，以及杂交雄性与纯种雌性之间均存在不完全的机械隔离。值得注意的是，在机械隔离不完全的物种组合中，相较于同种雄性，雌性对杂交雄性或异种雄性表现出更强的抗拒行为与拒配倾向。这一发现表明，涉及雄性外生殖器的触觉不兼容可影响雌性的交配选择，并在物种形成早期构成阻碍基因交流的强效屏障。