Stölting Kai N, Wilson Anthony B
Zoological Museum, University of Zürich, Switzerland.
Bioessays. 2007 Sep;29(9):884-96. doi: 10.1002/bies.20626.
Pregnancy has been traditionally defined as the period during which developing embryos are incubated in the body after egg-sperm union. Despite strong similarities between viviparity in mammals and other vertebrate groups, researchers have historically been reluctant to use the term pregnancy for non-mammals in recognition of the highly developed form of viviparity in eutherians. Syngnathid fishes (seahorses and pipefishes) have a unique reproductive system, where the male incubates developing embryos in a specialized brooding structure in which they are aerated, osmoregulated, protected and likely provisioned during their development. Recent insights into physiological, morphological and genetic changes associated with syngnathid reproduction provide compelling evidence that male incubation in these species is a highly specialized form of reproduction akin to other forms of viviparity. Here, we review these recent advances, highlighting similarities and differences between seahorse and mammalian pregnancy. Understanding the changes associated with the parallel evolution of male pregnancy in the two major syngnathid lineages will help to identify key innovations that facilitated the development of this unique form of reproduction and, through comparison with other forms of live bearing, may allow the identification of a common set of characteristics shared by all viviparous organisms.
传统上，怀孕被定义为卵子与精子结合后，发育中的胚胎在体内孕育的时期。尽管哺乳动物和其他脊椎动物类群的胎生现象有很多相似之处，但由于真兽类胎生形式高度发达，研究人员历来不愿将“怀孕”一词用于非哺乳动物。海龙科鱼类（海马和管口鱼）具有独特的生殖系统，雄性在一个特殊的育儿结构中孕育发育中的胚胎，胚胎在发育过程中在该结构中获得氧气、进行渗透压调节、得到保护并可能获得营养供应。最近对与海龙科生殖相关的生理、形态和基因变化的深入了解提供了令人信服的证据，表明这些物种中的雄性孕育是一种高度特化的生殖形式，类似于其他形式的胎生。在这里，我们回顾这些最新进展，突出海马怀孕与哺乳动物怀孕之间的异同。了解两个主要海龙科谱系中雄性怀孕的平行进化所伴随的变化，将有助于确定促成这种独特生殖形式发展的关键创新，并且通过与其他胎生形式进行比较，可能有助于识别所有胎生物种共有的一组特征。
