TY - JOUR
T1 - Specialization and group size
T2 - Brain and behavioral correlates of colony size in ants lacking morphological astes
AU - Amador-Vargas, Sabrina
AU - Gronenberg, Wulfila
AU - Wcislo, William T.
AU - Mueller, Ulrich
N1 - Publisher Copyright:
© 2015 The Author(s) Published by the Royal Society. All rights reserved.
PY - 2015
Y1 - 2015
N2 - Group size in both multicellular organisms and animal societies can correlate with the degree of division of labour. For ants, the task specialization hypothesis (TSH) proposes that increased behavioural specialization enabled by larger group size corresponds to anatomical specialization of worker brains. Alternatively, the social brain hypothesis proposes that increased levels of social stimuli in larger colonies lead to enlarged brain regions in all workers, regardless of their task specialization. We tested these hypotheses in acacia ants (Pseudomyrmex spinicola), which exhibit behavioural but not morphological task specialization. In wild colonies, we marked, followed and tested ant workers involved in foraging tasks on the leaves (leaf-ants) and in defensive tasks on the host tree trunk (trunk-ants). Task specialization increased with colony size, especially in defensive tasks. The relationship between colony size and brain region volume was task-dependent, supporting the TSH. Specifically, as colony size increased, the relative size of regions within the mushroom bodies of the brain decreased in trunk-ants but increased in leaf-ants; those regions play important roles in learning and memory. Our findings suggest that workers specialized in defence may have reduced learning abilities relative to leaf-ants; these inferences remain to be tested. In societies with monomorphic workers, brain polymorphism enhanced by group size could be a mechanism by which division of labour is achieved.
AB - Group size in both multicellular organisms and animal societies can correlate with the degree of division of labour. For ants, the task specialization hypothesis (TSH) proposes that increased behavioural specialization enabled by larger group size corresponds to anatomical specialization of worker brains. Alternatively, the social brain hypothesis proposes that increased levels of social stimuli in larger colonies lead to enlarged brain regions in all workers, regardless of their task specialization. We tested these hypotheses in acacia ants (Pseudomyrmex spinicola), which exhibit behavioural but not morphological task specialization. In wild colonies, we marked, followed and tested ant workers involved in foraging tasks on the leaves (leaf-ants) and in defensive tasks on the host tree trunk (trunk-ants). Task specialization increased with colony size, especially in defensive tasks. The relationship between colony size and brain region volume was task-dependent, supporting the TSH. Specifically, as colony size increased, the relative size of regions within the mushroom bodies of the brain decreased in trunk-ants but increased in leaf-ants; those regions play important roles in learning and memory. Our findings suggest that workers specialized in defence may have reduced learning abilities relative to leaf-ants; these inferences remain to be tested. In societies with monomorphic workers, brain polymorphism enhanced by group size could be a mechanism by which division of labour is achieved.
KW - Acacia ants
KW - Brain anatomy
KW - Division of labour
KW - Pseudomyrmex spinicola
KW - Task specialization
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U2 - 10.1098/rspb.2014.2502
DO - 10.1098/rspb.2014.2502
M3 - Article
C2 - 25567649
AN - SCOPUS:84922551507
VL - 282
JO - Philosophical transactions of the Royal Society of London. Series B: Biological sciences
JF - Philosophical transactions of the Royal Society of London. Series B: Biological sciences
SN - 0962-8436
IS - 1801
M1 - 20142502
ER -