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.

Functional Protein Composition in Femoral Glands of Sand Lizards (Lacerta agilis)

“…Femoral glands are usually dimorphic and, in general, more developed in males than in females [ 10 , 12 , 13 ]. Recent comparative analyses suggested that FGs and other epidermal glands may have played a role in the evolution of sociality in this vertebrate group [ 14 ]. Indeed, it is well known that FG secretions are involved in many social interactions (reviewed in [ 12 ]).…”

Coevolution of social and communicative complexity in lemurs

“…Similarly, in lizards the basic morphological hardware to produce olfactory signals, i.e. the number of chemical signalling glands, correlated with social grouping [23], suggesting that this rather rough proxy of communicative complexity is sufficient to invoke convergent coevolution with social complexity.…”

“…In birds, cooperative breeders exhibit larger vocal repertoires [19,20], experimental manipulations of group size caused changes in song complexity [21] and group-living facilitated duetting [22]. In lizards, social grouping covaries positively with the number of chemical signalling glands [23], whereas the visual display repertoire size is inversely associated with home range size [24]. Finally, in insects, sensory systems and chemical signals coevolved with group-living in halictid bees [25].…”

Evolutionary history of mental glands in turtles reveals a single origin in an aquatic ancestor and recurrent losses independent of macrohabitat

“…Multiple factors unrelated with alternative communication channels have been shown to influence epidermal glands and chemical signals in reptiles. For instance, sociality in lizards is associated with the presence of femoral glands indicating an important role of chemosignaling on squamate social grouping 78 . In addition, the composition of chemical signals produced by femoral glands is shaped by diet 79 – 81 , climate conditions 25 , 82 and predation pressure 83 .…”