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

Abstract

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.

Keywords: animal signals; epidermal gland secretions; lizard communication; social evolution; squamates.

Figure 1.

Coevolution of social grouping and epidermal glands in lizards. (a) Phylogenetic relationships [48] among the 911 lizard species included in our study with the colours at the tree tips indicating the absence (red) or presence (blue) of epidermal glands. Additional black dots denote the presence of social grouping in a species. (b) Rates of transition estimated using MuSSE modelling; the transition rate to social grouping from a state of ‘epidermal glands present’ is higher than from a state of ‘epidermal glands absent’ (table 2). (c) Histogram showing the fraction of a stochastic character mapping that is shared between the reconstructed trees of social grouping and epidermal glands. The mean similarity (0.63) is significantly higher than 0.5, indicating correlated evolution between social grouping and epidermal glands. Asterisks denote p < 0.001.