On Being Small: Brain Allometry in Ants

Wehner, Rüdiger; Fukushi, Tsukasa; Isler, Karin

doi:10.1159/000097057

Cited by 75 publications

(77 citation statements)

References 107 publications

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“…These results underline the need in future studies to distinguish between calyces when studying brain anatomy, and to explore the respective functional differences. Although previous studies have shown that workers from some species with larger colonies have larger brains [18,52], we did not find evidence in P. spinicola of an increase in absolute brain size with colony size. Instead, we found a small taskdependent effect of colony size on absolute brain volume (interaction between colony size and type of ant explained 3.4% of the variation).…”

Section: (A) Behavioural Tests Of Task Specialization Hypothesiscontrasting

confidence: 99%

Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes

et al. 2015

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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.

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Section: (A) Behavioural Tests Of Task Specialization Hypothesiscontrasting

confidence: 99%

Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes

et al. 2015

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“…The lack of functional senescence in P. dentata minor workers, underscored by the maintenance of neuroanatomical and neurochemical substrates that activate and support task performance, suggests that the ant nervous system has evolved robust functionality throughout the relatively short sterile worker lifespan. This resilience may be associated with energy savings resulting from the absence of reproductive costs of workers, reduced neuron and neural circuit size, and lower requirements for redundancy and information storage that could minimize neurometabolic costs in individual worker brains [76][77][78][79]. Additionally, the benefits of living in a highly integrated homeostatic social system capable of collective information processing and emergent cognition may allocate cost reductions in brain rspb.royalsocietypublishing.org Proc.…”

Section: Discussionmentioning

confidence: 99%

Lifespan behavioural and neural resilience in a social insect

et al. 2016

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Analyses of senescence in social species are important to understanding how group living influences the evolution of ageing in society members. Social insects exhibit remarkable lifespan polyphenisms and division of labour, presenting excellent opportunities to test hypotheses concerning ageing and behaviour. Senescence patterns in other taxa suggest that behavioural performance in ageing workers would decrease in association with declining brain functions. Using the ant Pheidole dentata as a model, we found that 120-day-old minor workers, having completed 86% of their laboratory lifespan, showed no decrease in sensorimotor functions underscoring complex tasks such as alloparenting and foraging. Collaterally, we found no age-associated increases in apoptosis in functionally specialized brain compartments or decreases in synaptic densities in the mushroom bodies, regions associated with integrative processing. Furthermore, brain titres of serotonin and dopamine-neuromodulators that could negatively impact behaviour through age-related declines-increased in old workers. Unimpaired task performance appears to be based on the maintenance of brain functions supporting olfaction and motor coordination independent of age. Our study is the first to comprehensively assess lifespan task performance and its neurobiological correlates and identify constancy in behavioural performance and the absence of significant age-related neural declines.

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“…Linear regression analyses were used to study the relationships between log CD, log M b and log L j . Because a major focus of this investigation involved intraspecific studies, we assumed a normal bivariate distribution and used ordinary least-squares regression as suggested by previous allometric investigations (Wehner et al, 2007) [see also p. vii in Calder (Calder, 1996)]. …”

Section: Methodsmentioning

confidence: 99%

Chewing rates among domestic dog breeds

Gerstner

Cooper

Peter

2010

Journal of Experimental Biology

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SUMMARYThe mammalian masticatory rhythm is produced by a brainstem timing network. The rhythm is relatively fixed within individual animals but scales allometrically with body mass (M b ) across species. It has been hypothesized that sensory feedback and feedforward adjust the rhythm to match the jaw's natural resonance frequency, with allometric scaling being an observable consequence. However, studies performed with adult animals show that the rhythm is not affected by jaw mass manipulations, indicating that either developmental or evolutionary mechanisms are required for allometry to become manifest. The present study was performed to tease out the relative effects of development versus natural selection on chewing rate allometry. Thirtyone dog breeds and 31 mass-matched non-domestic mammalian species with a range in M b from ~2kg to 50kg were studied. Results demonstrated that the chewing rhythm did not scale with M b among dog breeds (R0.299, P>0.10) or with jaw length (L j ) (R0.328, P>0.05). However, there was a significant relationship between the chewing rhythm and M b among the non-domestic mammals (R0.634, P<0.001). These results indicate that scaling is not necessary in the adult animal. We conclude that the central timing network and related sensorimotor systems may be necessary for rhythm generation but they do not explain the 1/3rd to 1/4th allometric scaling observed among adult mammals. The rhythm of the timing network is either adjusted to the physical parameters of the jaw system during early development only, is genetically determined independently of the jaw system or is uniquely hard-wired among dogs and laboratory rodents.

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On Being Small: Brain Allometry in Ants

Cited by 75 publications

References 107 publications

Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes

Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes

Lifespan behavioural and neural resilience in a social insect

Chewing rates among domestic dog breeds

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