Considerable controversy exists about which hypotheses and variables best explain mammalian brain size variation. We use a new, high-coverage dataset of marsupial brain and body sizes, and the first phylogenetically imputed full datasets of 16 predictor variables, to model the prevalent hypotheses explaining brain size evolution using phylogenetically corrected Bayesian generalized linear mixed-effects modelling. Despite this comprehensive analysis, litter size emerges as the only significant predictor. Marsupials differ from the more frequently studied placentals in displaying a much lower diversity of reproductive traits, which are known to interact extensively with many behavioural and ecological predictors of brain size. Our results therefore suggest that studies of relative brain size evolution in placental mammals may require targeted co-analysis or adjustment of reproductive parameters like litter size, weaning age or gestation length. This supports suggestions that significant associations between behavioural or ecological variables with relative brain size may be due to a confounding influence of the extensive reproductive diversity of placental mammals.

College of Science and Engineering Flinders University Australia

Department of Animal Biology University of Illinois at Urbana Champaign USA

Department of Ecology and Evolutionary Biology College of Life Sciences University of California Los Angeles CA USA

Department of Life Sciences Natural History Museum London UK

Faculty of Mechatronics Informatics and Interdisciplinary Studies Technical University of Liberec Czechia

Genetics Evolution and Environment Department University College London UK

School of Biological Sciences The University of Queensland St Lucia Queensland Australia

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Testing hypotheses of marsupial brain size variation using phylogenetic multiple imputations and a Bayesian comparative framework

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Dryad
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