Polistes smithii vs. Polistes dominula: the contrasting endocrinology and epicuticular signaling of sympatric paper wasps in the field

Paper wasps of the family Vespidae exhibit a wide range of social lifestyles, from facultative eusocial groups to highly ritualistic swarm-founding societies. Even so, adult caste flexibility is widespread throughout the eusocial tribes. Thus, a common endocrine mechanism for caste determination and maintenance in paper wasps is expected, with Polistes dominula serving as a model for the study of mechanisms controlling phenotypic plasticity. In P. dominula, juvenile hormone (JH) and ecdysteroids have been shown to have important caste-determining functions, are important for reproductive growth, and correlate with hydrocarbon signals on the cuticle. Yet research on swarm-founding vespids has shown that JH functions are surprisingly labile, begging the question as to how conserved JH functions are within Polistes, a non-swarming genus. Here, we compared the JH and ecdysteroid titers, cuticular hydrocarbon (CHC) profiles, and prospective visual signals of dominance of free-living foundresses from two sympatric and closely related species of Polistes in South Africa, the indigenous Polistes smithii and the invasive P. dominula. In contrast to P. dominula, neither the JH titer nor the CHC profile was linked to dominance or reproduction in P. smithii, and in both species, hemolymph ecdysteroids were essentially absent. Moreover, many of the relationships between hormones, reproduction, dominance, and social signals in P. dominula are in contrast to studies performed on northern hemisphere populations. The divergence of endocrine and chemical profiles within Polistes offers an unforeseen opportunity to study the evolution of proximate mechanisms underlying phenotypic plasticity.