Variation in DNA methylation is not consistently reflected by CpG depletion or sociality in Hymenoptera

Authors: GLASTAD, KARL - University Of Pennsylvania; ARSENAULT, SAMUEL - University Of Georgia; VERTACNIK, KIM - University Of Kentucky; Geib, Scott; KAY, SASHA - University Of Georgia; DANFORTH, BRYAN - Cornell University; REHAN, SANDRA - University Of New Hampshire; LINNEN, CATHERINE - University Of Kentucky; KOCHER, SARAH - Princeton University; HUNT, BRENDAN - University Of Georgia

Submitted to: Genome Biology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2017
Publication Date: 7/11/2017
Citation: Glastad, K.M., Arsenault, S.V., Vertacnik, K.L., Geib, S.M., Kay, S., Danforth, B.N., Rehan, S.M., Linnen, C.R., Kocher, S.D., Hunt, B.G. 2017. Variation in DNA methylation is not consistently reflected by CpG depletion or sociality in Hymenoptera. Genome Biology and Evolution. doi:10.1093/gbe/evx128.

Interpretive Summary: Phenotypic plasticity – the ability of an organism to modify its phenotype in different environments – is often mediated by changes in gene regulation and associated epigenetic modifications. One exemplar of this type of plasticity is the social insects, where individuals from the same genetic background develop into reproductive queens and non-reproductive workers. It has been hypothesized that differences in one type of epigenetic modification, DNA methylation, correlates with variation in social behavior in this group. We tested this idea using nine species of bees, ants, wasps, and sawflies, and found no association between DNA methylation and social behavior. Furthermore, we demonstrate that a commonly-used metric to estimate DNA methylation, CpG content, shows substantial variation among taxa in its association with DNA methylation. This makes it an unreliable predictor for comparative studies.

Technical Abstract: Changes in gene regulation that underlie phenotypic evolution can be encoded directly in the DNA sequence or mediated by chromatin modifications such as DNA methylation. It has been hypothesized that the evolution of social behavior is associated with enhanced gene regulatory potential, which may include expansions in DNA methylation, in the genomes of Hymenoptera (bees, ants, wasps, and sawflies). Recently, this hypothesis garnered support from analyses of a commonly-used metric to estimate DNA methylation, CpG content. Here, we test this hypothesis using direct, nucleotide-level measures of DNA methylation across nine species of Hymenoptera. We demonstrate that the strength of correlation between CpG content and DNA methylation varies among Hymenoptera, making it an unreliable proxy for comparative studies. Further, we find no evidence that expansions in DNA methylation are a necessary precursor to the evolution of social behavior.