Department of Ecology & Evolutionary Biology, University of Toronto,Toronto, ON, Canada.
Evolution. 2012 Apr;66(4):1180-95. doi: 10.1111/j.1558-5646.2011.01514.x. Epub 2011 Dec 12.
The process of speciation is key to the origins of biodiversity, and yet the Caenorhabditis nematode model system has contributed little to this topic. Genetic studies of speciation in the genus are now feasible, owing to crosses between the recently discovered Caenorhabditis sp. 9 and the well-known C. briggsae producing fertile F(1) hybrid females. We dissected patterns of postzygotic reproductive isolation between these species by crossing eight isogenic strains of C. briggsae reciprocally with six strains of C. sp. 9. We determined that overall patterns of reproductive isolation are robust across these genetic backgrounds. However, we also quantified significant heritable variation within each species for interspecific hybrid incompatibilities for total adult progeny, egg-to-adult viability, and the percentage of male progeny. This demonstrates that intraspecific variation for interspecific hybrid incompatibility occurs despite extensive, albeit incomplete, reproductive isolation. Therefore, this emerging general phenomenon of variable reproductive isolation is not restricted to highly interfertile, early-stage incipient species, but also applies to species in the latest stages of the speciation process. Furthermore, we confirm Haldane's rule and demonstrate strongly asymmetric parent-of-origin effects (Darwin's corollary) that consistently manifest more extremely when hermaphroditic C. briggsae serves as maternal parent. These findings highlight Caenorhabditis as an emerging system for understanding the genetics of general patterns of reproductive isolation.
物种形成过程是生物多样性起源的关键，但秀丽隐杆线虫模式系统在这一主题上贡献甚少。由于最近发现的秀丽隐杆线虫 sp. 9 与广为人知的 C. briggsae 之间的杂交，现在可以对该属的物种形成进行遗传研究，从而产生了可育的 F(1)杂交雌性。我们通过将 C. briggsae 的 8 个同基因株系与 C. sp. 9 的 6 个株系相互杂交，剖析了这两个物种之间的合子后生殖隔离模式。我们确定，在这些遗传背景下，生殖隔离的总体模式是稳健的。然而，我们还在每个物种内量化了种间杂种不亲和性的可遗传性变异，包括总成虫后代、卵到成虫的存活率和雄性后代的比例。这表明，尽管存在广泛但不完全的生殖隔离，但种内的种间杂种不亲和性仍存在可遗传的变异。因此，这种新兴的普遍生殖隔离可变性现象不仅限于高度可育的早期阶段的初生种，也适用于物种形成过程的最新阶段的物种。此外，我们证实了 Haldane 法则，并证明了强烈的非对称亲源效应（达尔文的推论），当雌雄同体的 C. briggsae 作为母本时，这种效应表现得更为极端。这些发现强调了秀丽隐杆线虫作为理解生殖隔离一般模式遗传基础的新兴系统。
