Figure 2.

A predictive framework for understanding sociality via inquiline social parasites. The comparative framework considers trait deletions, gains and modifications in parasite–host systems and is adapted from [25]. Bell curves describe the expression of a single phenotype in the host species (blue, solid lines) and the social parasite species (red, dashed lines). The phenotype ‘deletion’ model (a,b) exposes traits required for free-living social organisms that are lost and downregulated in the social parasite. The phenotype ‘augmentation model’ (c,d) can be represented by trait gain, a shift to a novel phenotypic trait, a modification of trait function or the condition under which the trait is expressed. The phenotype ‘retention’ model (e) exposes traits that are likely to be essential for the integration into the host social life. The three models are not necessarily mutually exclusive, as suggested by [25,31–33]. (Online version in colour.)