Adaptive brain mosaicism and transcriptomics of division of labor in a socially complex ant.
Isabella B. Muratore1, Eva M. Fandozzi1, Alexa K. Huzar1, Faraz H. Zaidi1, Iulian Ilieş2, Sean P. Mullen1, James F. A. Traniello1,3. 1Department of Biology, Boston University, Boston, MA, United States; 2Heathcare Systems Engineering Institute, Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA, United States; 33. Graduate Program in Neuroscience, Boston University, Boston, MA, United States

Brain evolution is hypothesized to be driven by neural substrate requirements to regulate behavioral performance. We estimated relative neural investments required to perform tasks varying in sensory processing and motor demands across polymorphic and polyethic workers of the leafcutter ant Atta cephalotes, and quantified brain size and structure to test our model. Investment in sensory integration and motor functions was estimated to be greatest for mid-sized (media) workers that perform diverse leaf-harvesting tasks. The mushroom bodies (centers of sensory integration and learning) and the antennal lobes (olfactory input processing) were significantly larger in medias compared to the smallest (minims, fungal gardeners) and largest workers (majors, soldiers). We identified significant differences in brain gene expression levels, the most pronounced between majors and minims, although not all expression differences were driven by worker size. Enriched gene functional categories included sensory processing and metabolism. Our results suggest that variation in task performance requirements has selected for adaptive genetically regulated patterns of brain mosaic scaling.