Functional basis of the fecundity - longevity reversal in the ant Temnothorax rugatulus

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Social insect queens exhibit extraordinarily long lifespans and at the same time are highly fecund. In most other animals, these two life history traits are traded-off, that is individuals that invest a lot in reproduction pay the price of reduced longevity. Projects in our research unit aim at gaining a deeper understanding of the ultimate and proximate basis of this longevity/fecundity reversal. Here we focus on the ant Temnothorax rugatulus, which is not only a good model due the occurrence of three females castes and its ease of collection and lab maintenance, but which already revealed interesting insights during the 1st funding period. We could show that an experimental fertility induction in workers resulted in a life-span extension indicating that the two life history traits are positively linked even within each caste. The smaller microgyne queens can maintain the same fecundity due to a higher metabolic rate, but are unable to increase egg-laying rates following egg removal. However, the larger macrogynes can increase their fecundity when eggs are removed and we are currently analyzing how this affects gene expression. A completed transcriptome analyses contrasting brain versus fat body of young and old queens, which also differed strongly in fecundity, revealed the importance of several longevity genes and pointed to well-known longevity pathways, such as Toll and TOR signaling. We now aim to elucidate the functional basis of the fecundity and longevity reversal in this ant, by analysing the regulation and connectivity of candidate genes in gene regulatory pathways. To do so, we plan a number of experimental manipulations using RNAi to demonstrate causal relationships between different genes and pathways and to reveal the effect of candidate genes on queen and worker fecundity and longevity. Moreover, we will study epigenetic mechanisms regulating expression in these pathways by experimentally inhibiting histone (de-)acetylation and DNA methylation. Thereafter, we will not only analyse how these manipulations affect the ability of queens and workers to change their fecundity, but we will also follow up with ChipSeq, Bisulfite sequencing, and RNA seq to directly check how these epigenetic processes and in turn gene regulation was affected. Our own data and especially those of Bernadau & Heinze indicate an influence of diet and in particular of the protein content on ant fecundity and longevity, which we plan to manipulate and investigate in the second phase. Our project will thus address several levels and focusses on the two most divergent female castes, workers and macrogynes. With our comprehensive project we will contribute to the understanding of the proximate mechanisms and the ultimate factors that lead to the fecundity/ longevity reversal in social insects.