Abstract
The evolution of sociality in insects is associated with a major disruption in the paradigm of the trade-of between longevity and reproduction. Additionally, the fertility and contribution of the workers to colony reproduction is an area of conflict of interests between the queen and the workers and also among the workers. The stingless bees (Meliponini) are a group of particular interest for investigating both the disruption in the trade-off and the the reproductive conflict, because they present a high degree of variability in worker fertility. This makes these bees an interesting an important natural experiment for investigating parameters associated with the evolution of life history strategies in the context of sociality. Among the bees, the stingless bees and the honey bees (Apini) are the only two tribes that are highly eusocial. Yet different from the honey bees, which are represented by less than a dozen extant species, all of which are rather similar in behaviors, the stingless bees are highly diverse in terms of numbers of species and genera, nest structure, and life style. For this project we selected three species of stingless bees, Melipona quadrifasciata, Frieseomelitta and Scaptotrigona bipunctata, whose workers differ in terms of reproductive biology and aggressiveness. We will perform comparative transcriptome analyses for three key stages of the adult life cycle (newly emerged workers, nurses, and foragers) and for three types of tissues with different functions (brain, ovary, and fat body). Differentially expressed genes for each tissue, species, and among the three species will be characterized in terms of Gene Ontology (GO) categories and KEGG pathways. Another type of important functional information will be generated via the analysis of correlated gene expression networks (WGCNA). For M. quadrifasciata and F. varia the transcritpome analyses can be based on their previously sequenced genomes, while for S. bipunctata we propose to also sequence and annotate its genome as part of this project, as the third species of this tribe to have genome information publicly available for this and future large-scale comparative analyses. For the genes that stand out in the transcriptome analyses of the three stingless bees we will then perform searches in the transcriptome databases of the honey bee, A. mellifera for comparisons of gene expression outcomes across the two clades of highly eusocial bees, Apini and Meliponini. The sequences of these genes will also be used to reveal potential evidence of positive selection by comparison of their orthologs from the bee genomes that are currently available in public databases. On the stingless bee genes inferred from the transcriptome data and on a set of candidate genes known from A. mellifera to be involved in reproduction, ageing/immunosenescence, division of labor, aggression, and epigenetic processes. We will perform in-depth expression analyses by means of real time PCR assays. So as to reveal correlates with physiological contexts we will finally perform analyses of protein and lipid contents of the fat body and also of ecdysteroids and juvenile hormone in the hemolymph of the workers of the three focal stingless bee species. With this study, which is set within a phylogenetically well-circumscribed context, we expect to generate innovative insights into the molecular processes underlying the evolution of sociality in insects and, concomitantly, into the reconfiguration of the trade-off between longevity and reproduction in life history theory. (AU)
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