Institute of Evolutionary Medicine, University of Zurich, Wintherthurerstrasse 190, 8057 Zurich, Switzerland.
Department of Biology, Geology, and Environmental Science, University of Tennessee at Chattanooga, USA.
Proc Biol Sci. 2020 May 13;287(1926):20200035. doi: 10.1098/rspb.2020.0035. Epub 2020 May 6.
Previous studies to understand the evolution of specific variation in mammalian social organization (SO; composition of social units) produced inconsistent results, possibly by ignoring specific variation. Here we present systematic data on SO in artiodactyl populations, coding SO as solitary, pair-living, group-living, sex-specific or variable (different kinds of SOs in the same population). We found that 62% of 245 populations and 83% of species (83/100) exhibited variable SO. Using Bayesian phylogenetic mixed-effects models, we simultaneously tested whether research effort, habitat, sexual dimorphism, breeding seasonality or body size predicted the likelihood of different SOs and inferred the ancestral SO. Body size and sexual dimorphism were strongly associated with different SOs. Contingent on the small body size (737 g) and putative sexual monomorphism of the earliest fossil artiodactyl, the ancestral SO was most likely to be pair-living (probability = 0.76, 95% CI = 0-1), followed by variable ( = 0.19, 95% CI = 0-0.99). However, at body size values typical of extant species, variable SO becomes the dominant form ( = 0.74, 95% CI = 0.18-1.00). Distinguishing different kinds of 'variable' highlights transitions from SOs involving pair-living to SOs involving solitary and/or group-living with increasing body size and dimorphism. Our results support the assumption that ancestral artiodactyl was pair-living and highlight the ubiquity of intraspecific variation in SO.
先前的研究旨在理解哺乳动物社会组织（SO；社会单位的组成）特定变异的进化，但得出的结果不一致，这可能是由于忽略了特定的变异。在这里，我们提供了有关偶蹄动物种群 SO 的系统数据，将 SO 编码为独居、双栖、群居、性别特定或可变（同一种群中有不同类型的 SO）。我们发现，在 245 个种群中有 62%，在 100 个物种中有 83%（83/100）表现出可变的 SO。我们使用贝叶斯系统发育混合效应模型，同时测试了研究努力、栖息地、性二态性、繁殖季节性或体型是否预测了不同 SO 的可能性，并推断了祖先 SO。体型和性二态性与不同的 SO 密切相关。取决于最早的化石偶蹄动物的小体型（737 克）和假定的性单态性，祖先 SO 最有可能是双栖（概率 = 0.76，95%置信区间= 0-1），其次是可变的（= 0.19，95%置信区间= 0-0.99）。然而，在现存物种典型的体型值下，可变 SO 成为主要形式（= 0.74，95%置信区间= 0.18-1.00）。区分不同种类的“可变”突出了随着体型和二态性的增加，从涉及双栖的 SO 到涉及独居和/或群居的 SO 的转变。我们的结果支持了祖先偶蹄动物是双栖的假设，并强调了 SO 种内变异的普遍性。
