Panhuis Tami M, Fris Megan, Tuhela Laura, Kwan Lucia
Department of Zoology, Ohio Wesleyan University, 61 S. Sandusky St, Delaware, Ohio, 43015.
Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks St, Toronto, Ontario, Canada, M5S 3B2.
J Morphol. 2017 Dec;278(12):1726-1738. doi: 10.1002/jmor.20745. Epub 2017 Aug 28.
In viviparous, teleost fish, with postfertilization maternal nutrient provisioning, embryonic structures that facilitate maternal-fetal nutrient transfer are predicted to be present. For the family Poeciliidae, only a handful of morphological studies have explored these embryonic specializations. Here, we present a comparative morphological study in the viviparous poeciliid genus, Poeciliopsis. Using microscopy techniques, we examine the embryonic surface epidermis of Poeciliopsis species that vary in their level of postfertilization maternal nutrient provisioning and placentation across two phylogenetic clades and three independent evolutionary origins of placentation. We focus on surface features of the embryo that may facilitate maternal-fetal nutrient transfer. Specifically, we studied cell apical-surface morphology associated with the superficial epithelium that covers the body and sac (yolk and pericardial) of embryos at different developmental stages. Scanning electron microscopy revealed common surface epithelial cells across species, including pavement cells with apical-surface microridges or microvilli and presumed ionocytes and/or mucus-secreting cells. For three species, in the mid-stage embryos, the surface of the body and sac were covered in microvillus epithelium. The remaining species did not display microvillus epithelium at any of the stages examined. Instead, their epithelium of the body and sac were composed of cells with apical-surface microridges. For all species, in the late stage embryos, the surface of the body proper was composed of apical-surface microridges in a "fingerprint-like arrangement." Despite the differences in the surface epithelium of embryos across Poeciliopsis species and embryonic developmental stages, this variation was not associated with the level of postfertilization maternal nutrient provisioning. We discuss these results in light of previous morphological studies of matrotrophic, teleost fish, phylogenetic relationships of Poeciliopsis species, and our earlier comparative microscopy work on the maternal tissue of the Poeciliopsis placenta.
在具有受精后母体营养供应的胎生硬骨鱼类中，预计会存在促进母胎营养转移的胚胎结构。对于食蚊鱼科来说，只有少数形态学研究探索过这些胚胎特化结构。在此，我们展示了对胎生食蚊鱼属Poeciliopsis的一项比较形态学研究。利用显微镜技术，我们检查了Poeciliopsis物种的胚胎表面表皮，这些物种在受精后母体营养供应水平和胎盘形成方面存在差异，跨越两个系统发育分支以及胎盘形成的三个独立进化起源。我们关注胚胎的表面特征，这些特征可能有助于母胎营养转移。具体而言，我们研究了与覆盖不同发育阶段胚胎身体和囊（卵黄和心包）的表层上皮相关的细胞顶端表面形态。扫描电子显微镜揭示了不同物种间常见的表面上皮细胞，包括具有顶端表面微嵴或微绒毛的扁平细胞以及推测的离子细胞和/或黏液分泌细胞。对于三个物种，在胚胎中期，身体和囊的表面覆盖着微绒毛上皮。其余物种在任何检查阶段都未显示微绒毛上皮。相反，它们身体和囊的上皮由具有顶端表面微嵴的细胞组成。对于所有物种，在胚胎后期，身体本身的表面由呈“指纹状排列”的顶端表面微嵴组成。尽管Poeciliopsis物种和胚胎发育阶段的胚胎表面上皮存在差异，但这种变化与受精后母体营养供应水平无关。我们根据先前对滋养型硬骨鱼类的形态学研究、Poeciliopsis物种的系统发育关系以及我们早期对Poeciliopsis胎盘母体组织的比较显微镜研究结果来讨论这些结果。
