Understanding the relative importance of various reproductive barriers to the early stages of speciation is an essential question in evolutionary biology. The closely related killifishes Fundulus heteroclitus and F. grandis occasionally hybridize in a small region in coastal Northeastern Florida showing that while barriers to reproduction exist, they are incomplete. The objective of this study was to elucidate barriers to reproduction between F. heteroclitus and F. grandis in the lab, as well as to quantify their strengths and relative contributions to reproductive isolation. Pre-zygotic (mating and fertilization) and post-zygotic (hatching) barriers were investigated by performing a variety of choice and no-choice laboratory mating experiments. Under no-choice conditions, barriers to mating had the greatest influence on hybrid production in F. grandis, whereas hatching barriers contributed to the majority of reproductive isolation in F. heteroclitus. Under choice conditions, however, pre-zygotic barriers had the greatest influence on hybrid production in both species. The total reproductive isolation that was observed in females of each species was stronger in F. heteroclitus than in F. grandis, and was nearly complete in F. heteroclitus females under choice conditions and was of moderate strength in F. grandis females. These results reveal an asymmetry in the potential gene flow between these two species, with F. grandis being more likely to hybridize than F. heteroclitus in the absence of environmental influences. No-choice backcrosses were also conducted and showed that at least some F1 hybrids are fertile. The observation that pre-zygotic barriers tend to be stronger than post-zygotic barriers in the early stages of speciation is consistent with similar studies in other organisms.

中文翻译：

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两种自然杂交K鱼物种之间生殖隔离障碍的量化

了解各种生殖障碍对物种形成早期的相对重要性是进化生物学中的一个基本问题。在佛罗里达州东北部沿海的一个小区域，紧密相关的双吻鱼类Fundulus heteroclitus和F. grandis偶尔杂交，表明尽管存在繁殖障碍，但它们并不完整。这项研究的目的是阐明异种和大种之间的繁殖障碍。在实验室中，以及量化它们的优势以及对生殖隔离的相对贡献。通过进行各种选择和无选择的实验室交配实验，研究了合子前（交配和受精）和合子后（孵化）的障碍。在别无选择的情况下，交配壁垒对混合动力的生产影响最大F.桉，而孵化障碍，促进了广大生殖隔离的F. heteroclitus。然而，在选择条件下，合子前屏障对两个物种的杂种生产影响最大。在每个物种的雌性中观察到的总生殖隔离在异形镰刀菌中比在大镰刀菌中更强。，并在接近完成F. heteroclitus女性选择的条件下，是中等强度的F.茅女性。这些结果揭示了这两个物种之间潜在的基因流动的不对称性，在没有环境影响的情况下，大花镰刀菌比杂种镰刀菌更可能杂交。还进行了非选择回交，表明至少一些F1杂种可育。在物种形成的早期阶段，合子前的障碍往往比合子后的障碍更强的观察结果与其他生物的类似研究一致。