Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Final Report Summary - ANTEPIGENETICS (The role of epigenetics in the regulation of reproduction and behavior in insect societies)

Reproductive and behavioral division of labor is at the root of the ecological success of insect societies, yet the mechanisms regulating reproduction and behavior are not fully understood. The clonal raider ant Cerapachys biroi has no distinct queen and worker castes, and is characterized by an alternation between reproductive phases (ants lay eggs inside the nest) and brood care phases (ants do not lay eggs but nurse the brood and forage for food). The opportunity to compare queen-like (reproductive phase) and worker-like (brood care phase) individuals, combined with the possibility to control for age, experience and genetic background (all known to influence reproduction and behavior), makes C. biroi a great model system to study division of labor. In the past few years, there has been a growing interest in the role of epigenetic mechanisms (e.g. DNA methylation) in social insect division of labor, but most studies lacked biological replicates and/or did not use comparable tissues.

The main objective of the AntEpigenetics project was to conduct a carefully replicated and controlled study of the role of DNA methylation in regulating reproduction and behavior in C. biroi, by comparing whole-genome DNA methylation patterns (using bisulfite sequencing) between brains of individuals collected in reproductive and brood care phases. This required to perform whole-genome bisulfite sequencing to assess the existence of differential patterns of DNA methylation, expression and splicing between the phases in the clonal raider ant.

During the outgoing phase at the Rockefeller University in New York City, I have performed methylation sensitive AFLP (amplified fragment length polymorphism), bisulfite sequencing and RNA sequencing on Cerapachys biroi brains. During the return phase at the University of Lausanne (Switzerland), I have analyzed the data collected during the outgoing phase. The analyses of the whole-genome bisulfite sequencing data revealed that many cytosines were methylated in all replicates (on average 29.5% of the methylated cytosines in a given replicate), indicating that a large proportion of the C. biroi brain methylome is robust. Robust DNA methylation occurred preferentially in exonic CpGs of highly and stably expressed genes involved in core functions. Our analyses did not detect any differences in DNA methylation between the queen-like and worker-like phases, suggesting that DNA methylation is not associated with changes in reproduction and behavior in C. biroi. Finally, many cytosines were methylated in one sample only, due to either biological or experimental variation. By applying the statistical methods used in previous unreplicated studies to our data, we show that such sample-specific DNA methylation may underlie the previous findings of queen- and worker-specific methylation. We argue that there is currently no evidence that genome-wide variation in DNA methylation is associated with the queen and worker castes in social insects, and we call for a more careful interpretation of the available data. The publication of this study (Libbrecht et al. 2016, Current Biology 26(3), 391-395) provides important insights into the function of DNA methylation in insect societies.

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