Energetic trade-offs between brain size and offspring production: Marsupials confirm a general mammalian pattern


  • Karin Isler

    Corresponding author
    1. Anthropological Institute and Museum, University of Zurich-Irchel, Zurich, Switzerland
    • Anthropological Institute and Museum, University of Zurich-Irchel, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
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Recently, Weisbecker and Goswami presented the first comprehensive comparative analysis of brain size, metabolic rate, and development periods in marsupial mammals. In this paper, a strictly energetic perspective is applied to identify general mammalian correlates of brain size evolution. In both marsupials and placentals, the duration or intensity of maternal investment is a key correlate of relative brain size, but here I show that allomaternal energy subsidies may also play a role. In marsupials, an energetic constraint on brain size in adults is only revealed if we consider both metabolic and reproductive rates simultaneously, because a strong trade-off between encephalization and offspring production masks the positive correlation between basal metabolic rate and brain size in a bivariate comparison. In conclusion, starting from an energetic perspective is warranted to elucidate relations between ecology, social systems, life history, and brain size in all mammals.