The University of Sydney, School of Life and Environmental Sciences, Sydney, NSW, Australia; Macquarie University, Department of Biological Sciences, Faculty of Science and Engineering, Macquarie Park, NSW, Australia.
The University of Sydney, School of Life and Environmental Sciences, Sydney, NSW, Australia.
Placenta. 2021 Oct;114:115-123. doi: 10.1016/j.placenta.2021.09.002. Epub 2021 Sep 3.
Embryonic growth and development require efficient respiratory gas exchange. Internal incubation of developing young thus presents a significant physiological challenge, because respiratory gas diffusion to embryos is impeded by the additional barrier of parental tissue between the embryo and the environment. Therefore, live-bearing species exhibit a variety of adaptations facilitating respiratory gas exchange between the parent (usually the mother) and embryos. Syngnathid fishes are the only vertebrates to exhibit male pregnancy, allowing comparative studies of the biology and evolution of internal incubation of embryos, independent of the female reproductive tract. Here, we examine the fleshy, sealed, seahorse brood pouch, and provide the first quantification of structural changes to this gestational organ across pregnancy.
We used histological analysis and morphometrics to quantify the surface area for exchange across the brood pouch epithelium, and the structure of the vascular bed of the brood pouch.
We show dramatic remodelling of gestational tissues as pregnancy progresses, including an increase in tortuosity of the gestational epithelium, an increase in capillary density, and a decrease in diffusion distance between capillaries and the pouch lumen.
These changes produce an increased surface area and expansion of the vascular bed of the placenta that likely facilitates respiratory gas exchange. These changes mirror the remodelling of gestational tissue in viviparous amniotes and elasmobranchs, and provide further evidence of the convergence of adaptations to support pregnancy in live-bearing animals.
胚胎的生长和发育需要高效的呼吸气体交换。因此，内部孵化的年轻胚胎面临着巨大的生理挑战，因为胚胎与环境之间的母体组织会阻碍呼吸气体扩散。因此，胎生动物表现出多种适应性，以促进亲代（通常是母亲）和胚胎之间的呼吸气体交换。海龙目鱼类是唯一表现出雄性怀孕的脊椎动物，允许对胚胎内部孵化的生物学和进化进行独立于雌性生殖道的比较研究。在这里，我们研究了肉质、密封的海马育儿袋，并首次对妊娠过程中这个妊娠器官的结构变化进行了定量分析。
我们使用组织学分析和形态计量学来量化育儿袋上皮的交换表面积，以及育儿袋血管床的结构。
我们发现妊娠过程中妊娠组织发生了剧烈的重塑，包括妊娠上皮的曲折度增加、毛细血管密度增加以及毛细血管与袋腔之间的扩散距离减少。
这些变化产生了更大的表面积和胎盘血管床的扩张，可能促进了呼吸气体交换。这些变化反映了胎生羊膜动物和软骨鱼纲动物妊娠组织的重塑，进一步证明了支持胎生动物妊娠的适应性趋同。
