School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Private Bag 3, WITS 2050, Johannesburg, South Africa.
IPHC, UNISTRA, CNRS, 23 rue du Loess, 67200 Strasbourg, France.
Proc Biol Sci. 2022 Oct 26;289(1985):20221589. doi: 10.1098/rspb.2022.1589.
It is generally believed that marsupials are more primitive than placentals mammals and mainly solitary living, representing the ancestral form of social organization of all mammals. However, field studies have observed pair and group-living in marsupial species, but no comparative study about their social evolution was ever done. Here, we describe the results of primary literature research on marsupial social organization which indicates that most species can live in pairs or groups and many show intra-specific variation in social organization. Using Bayesian phylogenetic mixed-effects models with a weak phylogenetic signal of 0.18, we found that solitary living was the most likely ancestral form (35% posterior probability), but had high uncertainty, and the combined probability of a partly sociable marsupial ancestor (65%) should not be overlooked. For Australian marsupials, group-living species were less likely to be found in tropical rainforest, and species with a variable social organization were associated with low and unpredictable precipitation representing deserts. Our results suggest that modern marsupials are more sociable than previously believed and that there is no strong support that their ancestral state was strictly solitary living, such that the assumption of a solitary ancestral state of all mammals may also need reconsideration.
人们普遍认为，有袋类动物比胎盘哺乳动物更为原始，主要是独居生活，代表了所有哺乳动物社会组织的原始形式。然而，野外研究已经观察到有袋类物种的成对和群体生活，但从未对其社会进化进行过比较研究。在这里，我们描述了对有袋类社会组织的主要文献研究的结果，该研究表明，大多数物种可以成对或成群生活，许多物种在社会组织方面表现出种内变异。使用具有弱系统发育信号（0.18）的贝叶斯系统发育混合效应模型，我们发现独居生活是最可能的祖先形式（35%的后验概率），但具有很高的不确定性，部分群居有袋类动物祖先（65%）的组合概率也不容忽视。对于澳大利亚有袋动物，群体生活的物种在热带雨林中较少见，而社会组织具有可变性的物种与低且不可预测的降水有关，代表了沙漠。我们的研究结果表明，现代有袋动物比以前认为的更具社会性，而且没有强有力的证据表明它们的祖先状态是严格的独居生活，因此，所有哺乳动物的祖先状态可能也是独居的假设也需要重新考虑。
