Geographic patterns in the distribution of social systems in terrestrial arthropods

Abstract

The role of ecology in the evolution and maintenance of arthropod sociality has received increasing research attention in recent years. In some organisms, such as halictine bees, polistine wasps, and social spiders, researchers are investigating the environmental factors that may contribute to high levels of variation in the degree of sociality exhibited both among and within species. Within lineages that include only eusocial members, such as ants and termites, studies focus more on identifying extrinsic factors that may contribute to the dramatic variation in colony size, number of queens, and division of labour that is evident across these species. In this review, I propose a comparative approach that seeks to identify environmental factors that may have a common influence across such divergent social arthropod groups. I suggest that seeking common biogeographic patterns in the distribution of social systems or key social traits may help us to identify ecological factors that play a common role in shaping the evolution of sociality across different organisms. I first review previous studies of social gradients that form along latitudinal and altitudinal axes. Within families and within species, many organisms show an increasing degree of sociality at lower latitudes and altitudes. In a smaller number of cases, organisms form larger groups or found nests cooperatively at higher latitudes and altitudes. I then describe several environmental factors that vary consistently along such gradients, including climate variables and abundance of predators, and outline their proposed role in the social systems of terrestrial arthropods. Finally, I map distributions of a social trait against several climatic factors in five case studies to demonstrate how future comparative studies could inform empirical research.

Transitions in social complexity along elevational gradients reveal a combined impact of season length and development time on social evolution

“…Similarly, in ants, species in 17 of 19 genera and five of six subfamilies tend to have larger colony sizes at high latitudes [2] (cf. [4]). …”

The Right Tools for the Job: Cooperative Breeding Theory and an Evaluation of the Methodological Approaches to Understanding the Evolution and Maintenance of Sociality

“…Many studies have focused on testing four key hypotheses of cooperative breeding theory (Table 1) using broad comparisons of relevant ecological, social and life history variables across multiple species of birds, mammals and insects (Cockburn, 1996;Arnold and Owens, 1998;Johnson et al, 2002;Purcell, 2011). Essentially, these studies have investigated the evolution of sociality by phylogenetic comparative analysis, comparing differences in key variables between multiple social and asocial species within a given lineage.…”

“…Comparative analyses are ideal for the study of large scale environmental influences on the evolution of sociality since their very aim is to compare patterns across multiple taxa or within a single species over large geographic areas. Such analyses have demonstrated that there is a non-random geographic distribution of sociality in a variety of taxa (Jetz and Rubenstein, 2011;Purcell, 2011). For example, Purcell (2011) conducted an extensive review of the literature pertaining to arthropod sociality along latitudinal and altitudinal gradients, and reanalyzed five previous case studies of social spiders and four ant subfamilies.…”

“…Such analyses have demonstrated that there is a non-random geographic distribution of sociality in a variety of taxa (Jetz and Rubenstein, 2011;Purcell, 2011). For example, Purcell (2011) conducted an extensive review of the literature pertaining to arthropod sociality along latitudinal and altitudinal gradients, and reanalyzed five previous case studies of social spiders and four ant subfamilies. It was found that climatic factors were correlated with variation in colony size, with social arthropod species occurring more frequently at lower latitudes.…”

“…The animal kingdom contains many examples of species, including our own, which form surprisingly complex social structures Purcell, 2011;Grueter et al, 2012;Chapais, 2013;Johnson et al, 2013;Taborsky and Wong, 2017). The size, structure and composition of these groups can vary both within and between species, from pair-bonding monogamous partners (Kleiman, 2011;Servedio et al, 2013) to large and highly complex societies exhibiting social hierarchies and division of labor (Duffy and Macdonald, 2010;Nandi et al, 2013).…”