Behaviour 2019
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Social complexity and brain metabolism in ants  
Zach Coto1, Eva Fandozzi1, Emily Hunter3, Frank Azorsa1, Isabella Muratore1, Sara Arganda1,4, Ignacio Arganda-Carreras 5,6,7, J. Francis Kamhi8, James Waters9, Jon Harrison10, Mario Muscedere1, James F.A. Traniello1,2. 1Department of Biology, Boston University, Boston, MA, United States; 2Graduate Program for Neuroscience, Boston University, Boston, MA, United States; 3Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, North Holland, Netherlands; 4Departamento de Biología y Geología, Física y Química, Inorgánica, Área de Biodiversidad y Conservación, Universidad Rey Juan Carlos, Madrid, Madrid, Spain; 5Ikerbasque, Basque Foundation for Science, Bilbao, Biscay, Spain; 6Dept. of Computer Science and Artificial Intelligence, Basque Country University, San Sebastian, , Spain; 7Donostia International Physics Center (DIPC), San Sebastian, , Spain; 8Department of Neuroscience, Oberlin College, Oberlin, OH, United States; 9Department of Biology, Providence College, Providence, RI, United States; 10School of Life Sciences, Arizona State University, Tempe, AZ, United States

Ants exhibit striking variation in social complexity, typically assessed in terms of colony size, emergent properties, division of labor, and worker polymorphism. Worker task performance demands may therefore vary across species in association with degrees of specialization and collective behavior, thus influencing neuroarchitecture. Although quantifying brain size and structure has been insightful, operation costs, which have rarely been measured, likely play a significant role in brain evolution. Workers in sister species of the ant genus Dolichoderus that vary in colony size and differ in brain mosaic structure showed no significant change in mass-specific brain metabolism. Workers of the highly polymorphic leafcutter ant Atta cephalotes that exhibit adaptive neural phenotypes showed patterns of brain metabolic scaling different from those of size-variable monomorphic ant species. These results suggest that variation in behavioral demands driving brain operation costs may be associated with division of labor by physical castes rather than variation in colony size.