Caste biased gene expression during early development in Pogonomyrmex ants

This study aims at investigating the molecular mechanisms underlying gyne and worker caste differentiation in early developmental stages in ants. To address this, we used Pogonomyrmex rugosus J lineages ants as their genetic caste-determination system allows to determine the caste-fate at any developmental stage via genotyping approaches. We used mRNA-seq to identify caste-biased genes and profile gene expression dynamics at five early developmental stages ranging between 24-hour old eggs and second instar larvae. We found differences in gene expression between gyne and worker-destined embryos as early as 24 hours after egg laying, and two developmental stages showed a burst of caste-biased genes, in 6 day old eggs and in the first instar larvae, which suggests that in P. rugosus J lineages, caste differentiation starts early in embryonic development. There were more worker-biased than gyne-biased genes in all five developmental stages, which supports the idea that the queen phenotype is the default developmental pathway in ants and worker developmental programs are actively switched on.