Phenotypic plasticity is important in adaptation and shapes the evolution of organisms. However, we understand little about what aspects of the genome are important in facilitating plasticity. Eusocial insect societies produce plastic phenotypes from the same genome, as reproductives (queens) and nonreproductives (workers). The greatest plasticity is found in the simple eusocial insect societies in which individuals retain the ability to switch between reproductive and nonreproductive phenotypes as adults. We lack comprehensive data on the molecular basis of plastic phenotypes. Here, we sequenced genomes, microRNAs (miRNAs), and multiple transcriptomes and methylomes from individual brains in a wasp (Polistes canadensis) and an ant (Dinoponera quadriceps) that live in simple eusocial societies. In both species, we found few differences between phenotypes at the transcriptional level, with little functional specialization, and no evidence that phenotype-specific gene expression is driven by DNA methylation or miRNAs. Instead, phenotypic differentiation was defined more subtly by nonrandom transcriptional network organization, with roles in these networks for both conserved and taxon-restricted genes. The general lack of highly methylated regions or methylome patterning in both species may be an important mechanism for achieving plasticity among phenotypes during adulthood. These findings define previously unidentified hypotheses on the genomic processes that facilitate plasticity and suggest that the molecular hallmarks of social behavior are likely to differ with the level of social complexity.

This work was funded by Natural Environment Research Council Grants NE/G000638/1, NBAF581, and NE/K011316/1 (to S.S.) and Grant NE/G012121/1 (to W.O.H.H. and S.S.); the Research Councils UK (S.S); the Cancer Research UK Grant C14303/A17197 (to S.B); the Leverhulme Trust (W.O.H.H.); German Federal Ministry of Education and Research Grant FKZ 0315962 B; CRG core funding (to H.H.); Spanish Ministry of Economy and Competitiveness (MINECO) Grant BIO2012-37161 (to T.G.); MINECO Grant BIO2011-26205 (to R.G.); Instituto de Salud Carlos III Grant PT13/0001/0021 (to R.G.); the Instituto Nacional de Bioinformatica and Agència de Gestió d’Ajuts Universitaris i de Recerca (R.G.); Wellcome Trust Grants 095645/Z/11/Z (to W.R.) and WT099232 (to S.B); Biotechnology and Biological Sciences Research Council Grant BB/K010867/1 (to W.R.); the Stuttgart Universität (T.P.J.); and Fundaçao de Amparo à Pesquisa do Estado de Sao Paulo Grant 2010/10027-5 (to F.S.N.).