Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany. kathleen
Biol Rev Camb Philos Soc. 2011 Feb;86(1):77-95. doi: 10.1111/j.1469-185X.2010.00135.x.
Superfetation is understood as another conception during an already ongoing pregnancy. This implies the existence of young of different developmental stages within the female reproductive tract during certain periods of pregnancy. Nevertheless, a clear definition of the term as well as distinct criteria to identify the occurrence of superfetation in a species is missing. The variable anatomy of mammalian reproductive tracts seems to make the occurrence of superfetation more or less likely but impedes the simple evaluation of whether it is present or not. Additionally, adequate determination methods are missing or are difficult to apply at the right time. Superfetation or rather superfetation-like pregnancies are reported for numerous species including humans, livestock and rodents. The usual criteria to assume a case of superfetation include the finding of discordantly developed young within the uterus during post mortem or parturition of young after a birth interval shorter than the assumed pregnancy length. Often the occurrence of superfetation is concluded because other explanations of reproductive artifacts are missing. Even severe reproductive pathologies are often confused with superfetation. True superfetation or superfetation as a reproductive strategy may exist in some mammals. In the American mink (Neovison (Mustela) vison) and the European badger (Meles meles) superfetation occurs in combination with embryonic diapause. In the European brown hare (Lepus europaeus), superfetation has long been assumed to exist but evidence is still controversial. Superfetation definitely occurs in certain species of poeciliid and zenarchopterid fish, some of which also exhibit viviparity and maternal care. In mammals, the evolution of such a reproductive mechanism poses many interesting evolutionary, endocrine, microbial and immunological questions that require further investigation. Here we review the scant and at times ancient literature on this poorly understood topic. The different manifestations of superfetation are defined and reliable criteria to detect superfetation are outlined. Also, the differentiation of superfetation into a reproductive strategy or as a disrupted, abnormal reproductive function is discussed. Due to the different discussed functional aspects of superfetation, it is appropriate to establish a more detailed scheme to classify the true natural superfetation cases into superfertilization, superconception and superfetation proper. To date, there is no mammal species known for which superfetation proper in terms of finding discordantly developed fetuses has been conclusively demonstrated to be not only a rare occurence but an evolved reproductive strategy.
超胎是指在已经进行中的妊娠期间再次受孕。这意味着在妊娠的某些阶段，女性生殖道内会存在不同发育阶段的胚胎。然而，对于这一术语，目前尚没有明确的定义，也没有明确的标准来确定物种中是否存在超胎。哺乳动物生殖道的解剖结构存在差异，这使得超胎的发生或多或少变得更加复杂，但也使得评估其是否存在变得更加困难。此外，目前还缺乏适当的确定方法，或者这些方法难以在正确的时间应用。超胎或类似超胎的妊娠在包括人类、家畜和啮齿动物在内的许多物种中都有报道。通常，假设存在超胎的依据包括在产后或在产仔间隔短于预期妊娠时间的情况下，在子宫内发现发育不同的胚胎。通常，由于其他生殖异常的解释缺失，人们会推断存在超胎。即使是严重的生殖病理学也常常与超胎相混淆。在某些哺乳动物中，真正的超胎或超胎作为一种生殖策略可能存在。在美洲水貂（Neovison （Mustela） vison）和欧洲獾（Meles meles）中，超胎与胚胎休眠相结合发生。在欧洲野兔（Lepus europaeus）中，长期以来人们一直认为存在超胎，但证据仍存在争议。在某些种类的胎生鱂鱼和胎生银汉鱼中，确实存在超胎，其中一些还具有胎生和母体照顾的特征。在哺乳动物中，这种生殖机制的进化带来了许多有趣的进化、内分泌、微生物和免疫学问题，需要进一步研究。在这里，我们回顾了关于这个了解甚少的主题的稀少且有时是古老的文献。定义了超胎的不同表现形式，并概述了检测超胎的可靠标准。此外，还讨论了将超胎分为生殖策略或作为一种破坏的、异常的生殖功能的区别。由于超胎具有不同的讨论功能方面，因此建立一个更详细的方案将真正的自然超胎病例分类为超受精、超妊娠和真正的超胎是合适的。迄今为止，还没有已知的哺乳动物物种被证明其真正的超胎，即发现发育不同的胎儿，不仅是一种罕见的情况，而且是一种进化的生殖策略。
