TY - JOUR
T1 - The evolution of relative brain size in marsupials is energetically constrained but not driven by behavioral complexity
AU - Weisbecker, Vera
AU - Blomberg, Simon
AU - Goldizen, Anne W.
AU - Brown, Meredeth
AU - Fisher, Diana
PY - 2015/5
Y1 - 2015/5
N2 - Evolutionary increases in mammalian brain size relative to body size are energetically costly but are also thought to confer selective advantages by permitting the evolution of cognitively complex behaviors. However, many suggested associations between brain size and specific behaviors-particularly related to social complexity-are possibly confounded by the reproductive diversity of placental mammals, whose brain size evolution is the most frequently studied. Based on a phylogenetic generalized least squares analysis of a data set on the reproductively homogenous clade of marsupials, we provide the first quantitative comparison of two hypotheses based on energetic constraints (maternal investment and seasonality) with two hypotheses that posit behavioral selection on relative brain size (social complexity and environmental interactions). We show that the two behavioral hypotheses have far less support than the constraint hypotheses. The only unambiguous associates of brain size are the constraint variables of litter size and seasonality. We also found no association between brain size and specific behavioral complexity categories within kangaroos, dasyurids, and possums. The largest-brained marsupials after phylogenetic correction are from low-seasonality New Guinea, supporting the notion that low seasonality represents greater nutrition safety for brain maintenance. Alternatively, low seasonality might improve the maternal support of offspring brain growth. The lack of behavioral brain size associates, found here and elsewhere, supports the general 'cognitive buffer hypothesis' as the best explanatory framework of mammalian brain size evolution. However, it is possible that brain size alone simply does not provide sufficient resolution on the question of how brain morphology and cognitive capacities coevolve.
AB - Evolutionary increases in mammalian brain size relative to body size are energetically costly but are also thought to confer selective advantages by permitting the evolution of cognitively complex behaviors. However, many suggested associations between brain size and specific behaviors-particularly related to social complexity-are possibly confounded by the reproductive diversity of placental mammals, whose brain size evolution is the most frequently studied. Based on a phylogenetic generalized least squares analysis of a data set on the reproductively homogenous clade of marsupials, we provide the first quantitative comparison of two hypotheses based on energetic constraints (maternal investment and seasonality) with two hypotheses that posit behavioral selection on relative brain size (social complexity and environmental interactions). We show that the two behavioral hypotheses have far less support than the constraint hypotheses. The only unambiguous associates of brain size are the constraint variables of litter size and seasonality. We also found no association between brain size and specific behavioral complexity categories within kangaroos, dasyurids, and possums. The largest-brained marsupials after phylogenetic correction are from low-seasonality New Guinea, supporting the notion that low seasonality represents greater nutrition safety for brain maintenance. Alternatively, low seasonality might improve the maternal support of offspring brain growth. The lack of behavioral brain size associates, found here and elsewhere, supports the general 'cognitive buffer hypothesis' as the best explanatory framework of mammalian brain size evolution. However, it is possible that brain size alone simply does not provide sufficient resolution on the question of how brain morphology and cognitive capacities coevolve.
KW - Brain size
KW - Constraint
KW - Life history
KW - Marsupials
KW - Maternal investment
KW - Seasonality
UR - http://www.scopus.com/inward/record.url?scp=84930179565&partnerID=8YFLogxK
UR - http://purl.org/au-research/grants/ARC/DE120102034
UR - http://purl.org/au-research/grants/ARC/DP140102656
UR - http://purl.org/au-research/grants/ARC/FT110100191
UR - http://purl.org/au-research/grants/ARC/DP0773920
U2 - 10.1159/000377666
DO - 10.1159/000377666
M3 - Article
C2 - 25966967
AN - SCOPUS:84930179565
VL - 85
SP - 125
EP - 135
JO - BRAIN BEHAVIOR AND EVOLUTION
JF - BRAIN BEHAVIOR AND EVOLUTION
SN - 0006-8977
IS - 2
ER -