Testing the reproductive groundplan hypothesis in ants (Hymenoptera: Formicidae)

The evolution of complex societies with obligate reproductive division of labour represents one of the major transitions in evolution. In such societies, functionally sterile individuals (workers) perform many of fitness-relevant behaviours including allomaternal ones, without getting any direct fitness benefits. The question of how such worker division of labour has evolved remains controversial. The reproductive groundplan hypothesis (RGPH) offers a powerful proximate explanation for this evolutionary leap. The RGPH argues that the conserved genetic and endocrinological networks regulating fitness relevant behaviour (e g. foraging and brood care) in their solitary ancestors have become decoupled from actual reproduction in the worker caste and now generate worker behavioural phenotypes. However, the empirical support for this hypothesis remains limited to a handful of species making its general validity uncertain. In this study we combine data from the literature with targeted sampling of key species and apply phylogenetically controlled comparative analysis to investigate if the key prediction of the RGPH, namely an association between allomaternal behaviour and a allomaternal physiological state holds in the largest and most species-rich clade of social insects, the ants. Our findings clearly support the RPGH as a general framework to understand the evolution of the worker caste and shed light on one of the major transition in evolutionary history.