title: Absolute, not relative brain size correlates with sociality in ground squirrels.
abstract: The social brain hypothesis (SBH) contends that cognitive demands associated with living in cohesive social groups favour the evolution of large brains. Although the correlation between relative brain size and sociality reported in various groups of birds and mammals provides broad empirical support for this hypothesis, it has never been tested in rodents, the largest mammalian order. Here, we test the predictions of the SBH in the ground squirrels from the tribe Marmotini. These rodents exhibit levels of sociality ranging from solitary and single-family female kin groups to egalitarian polygynous harems but feature similar ecologies and life-history traits. We found little support for the association between increase in sociality and increase in relative brain size. Thus, sociality does not drive the evolution of encephalization in this group of rodents, a finding inconsistent with the SBH. However, body mass and absolute brain size increase with sociality. These findings suggest that increased social complexity in the ground squirrels goes hand in hand with larger body mass and brain size, which are tightly coupled to each other.
authors.affiliation: Museum Karlovy Vary, Pod Jelením skokem 30, Karlovy Vary 360 01, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Matějů
authors.affiliation: Faculty of Science, Charles University in Prague, Viničná 7, Praha 2 128 44, Czech Republic.
authors.forename: Lukáš
authors.initials: L
authors.lastname: Kratochvíl
authors.affiliation: Faculty of Science, Charles University in Prague, Viničná 7, Praha 2 128 44, Czech Republic.
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Pavelková
authors.affiliation: Faculty of Science, University of South Bohemia, Branišovská 31, České Budějovice 370 05, Czech Republic.
authors.forename: Věra
authors.initials: V
authors.lastname: Pavelková Řičánková
authors.affiliation: Faculty of Science, Charles University in Prague, Viničná 7, Praha 2 128 44, Czech Republic.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Vohralík
authors.affiliation: Faculty of Science, Charles University in Prague, Viničná 7, Praha 2 128 44, Czech Republic pgnemec@natur.cuni.cz.
authors.forename: Pavel
authors.initials: P
authors.lastname: Němec
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology*; D005260:Female; D008297:Male; D009929:Organ Size; D012589:Sciuridae / Q000033:anatomy & histology* / Q000502:physiology*; D012727:Sex Characteristics; D012919:Social Behavior
keywords: Sciuridae; body size; brain evolution; mating system; sexual dimorphism; sociality