Investment in chemical signalling glands facilitates the evolution of sociality in lizards

The evolution of sociality and traits that correlate with, or predict, sociality, have been the focus of considerable recent study. In order to reduce the social conflict that ultimately comes with group living, and foster social tolerance, individuals need reliable information about group members and potential rivals. Chemical signals are one such source of information and are widely used in many animal taxa, including lizards. Here, we take a phylogenetic comparative approach to test the hypothesis that social grouping correlates with investment in chemical signalling. We used the presence of epidermal glands as a proxy of chemical investment and considered social grouping as the occurrence of social groups containing both adults and juveniles. Based on a dataset of 911 lizard species, our models strongly supported correlated evolution between social grouping and chemical signalling glands. The rate of transition towards social grouping from a background of ‘epidermal glands present’ was an order of a magnitude higher than from a background of ‘no epidermal glands’. Our results highlight the potential importance of chemical signalling during the evolution of sociality and the need for more focused studies on the role of chemical communication in facilitating information transfer about individual and group identity, and ameliorating social conflict.

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社会性及其与社交性相关的或预测社交性的特征，一直是近期研究的热点。为了减少群居生活所带来的最终社会冲突，并促进社会宽容，个体需要关于群体成员和潜在竞争对手的可靠信息。化学信号就是此类信息源之一，并且在许多动物类群中，包括蜥蜴类动物中，被广泛使用。在本研究中，我们采用系统发育比较方法，以检验社会分组与化学信号投资之间的相关性假说。我们以表皮腺体的存在作为化学投资的替代指标，并将社会分组视为包含成体和幼体的社会群体的出现。基于911种蜥蜴的数据集，我们的模型强烈支持了社会分组与化学信号腺体之间的相关进化。从‘表皮腺体存在’的背景向社会分组的转变速率，比从‘无表皮腺体’的背景转变的速率高出至少一个数量级。我们的研究结果突出了化学信号在社会性进化过程中的潜在重要性，以及需要更加聚焦于化学通讯在促进个体和群体身份信息传递、以及缓解社会冲突中所起作用的深入研究。