Data from: The evolution of diapause in Rivulus (Laimosemion)

Annual killifish adapted to life in aquatic habitat that seasonally dries have evolved desiccation resistant eggs capable of undergoing diapause, developmental arrest, at specific stages during embryology. Although noted for their remarkable abilities to live at the land-water interface, species in the genus Rivulus are considered non-annual killifish exhibiting typical teleost development patterns and no embryonic diapause. Here, we combine a molecular phylogeny with embryological study to demonstrate an independent origin of mid-embryonic diapause within a clade of Rivulus (subgenus Laimosemion) that inhabits small streams or savannah pools. We further observed that some of these species exhibit a short dispersed cell phase separating epiboly and the formation of the embryo axis – a feature of development only observed in annual killifish. Lastly, we incubated embryos of Laimosemion species and outgroup taxa in both water and peat moss, and observed that on peat moss embryos of all species are capable of delaying hatching for greater than 10 days, but when water-incubated there are significant differences among species in the length of this delay prior to hatching. We hypothesize that the preferred microhabitat of this clade of killifish exposes their embryos to periodic desiccation, creating selection in favor of embryonic diapause.适应于季节性干涸水生栖息地的一年生鳉鱼（annual killifish），已演化出耐干燥的卵，可在胚胎发育的特定阶段进入滞育（diapause）状态，即发育停滞。尽管溪鳉属（Rivulus）物种以其在水陆交界环境中生存的卓越能力为人所知，但该属物种被归类为非一年生鳉鱼，其胚胎发育模式符合典型硬骨鱼特征，且无胚胎滞育现象。本研究结合分子系统发育分析与胚胎学实验，证实溪鳉属（Rivulus）下的莱莫溪鳉亚属（Laimosemion）演化支内，独立演化出了胚胎中期滞育的特性；该亚属物种栖息于小型溪流或稀树草原水塘中。我们进一步观察到，该亚属部分物种存在一段短暂的细胞分散期，可分隔胚胎外包（epiboly）与胚胎轴形成两个发育阶段——这一特征此前仅在一年生鳉鱼中被发现。最后，我们对莱莫溪鳉亚属物种及其外类群的胚胎，分别在水环境与泥炭藓基质中开展孵化培养实验。结果显示：在泥炭藓基质中，所有受试物种的胚胎均可将孵化延迟至10天以上；而在水环境中，不同物种的孵化延迟时长存在显著差异。本研究据此提出假说：该鳉鱼演化支偏好的微生境会使其胚胎暴露于周期性干燥环境中，由此产生了倾向于胚胎滞育的自然选择压力。