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Abstract Metabolism, a metric of the energy cost of behavior, plays a significant role in social evolution. Body size and metabolic scaling are coupled, and a socioecological pattern of increased body size is associated with dietary change and the formation of larger and more complex groups. These consequences of the adaptive radiation of animal societies beg questions concerning energy expenses, a substantial portion of which may involve the metabolic rates of brains that process social information. Brain size scales with body size, but little is understood about brain metabolic scaling. Social insects such as ants show wide variation in worker body size and morphology that correlates with brain size, structure, and worker task performance, which is dependent on sensory inputs and information-processing ability to generate behavior. Elevated production and maintenance costs in workers may impose energetic constraints on body size and brain size that are reflected in patterns of metabolic scaling. Models of brain evolution do not clearly predict patterns of brain metabolic scaling, nor do they specify its relationship to task performance and worker ergonomic efficiency, two key elements of social evolution in ants. Brain metabolic rate is rarely recorded and, therefore, the conditions under which brain metabolism influences the evolution of brain size are unclear. We propose that studies of morphological evolution, colony social organization, and worker ergonomic efficiency should be integrated with analyses of species-specific patterns of brain metabolic scaling to advance our understanding of brain evolution in ants.
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Transcriptomic analysis of mosaic brain differentiation underlying complex division of labor in a social insect
Abstract Concerted developmental programming may constrain changes in component structures of the brain, thus limiting the ability of selection to form an adaptive mosaic of size‐variable brain compartments independent of total brain size or body size. Measuring patterns of gene expression underpinning brain scaling in conjunction with anatomical brain atlases can aid in identifying influences of concerted and/or mosaic evolution. Species exhibiting exceptional size and behavioral polyphenisms provide excellent systems to test predictions of brain evolution models by quantifying brain gene expression. We examined patterns of brain gene expression in a remarkably polymorphic and behaviorally complex social insect, the leafcutter antAtta cephalotes. The majority of significant differential gene expression observed among three morphologically, behaviorally, and neuroanatomically differentiated worker size groups was attributable to body size. However, we also found evidence of differential brain gene expression unexplained by worker morphological variation and transcriptomic analysis identified patterns not linearly correlated with worker size but sometimes mirroring neuropil scaling. Additionally, we identified enriched gene ontology terms associated with nucleic acid regulation, metabolism, neurotransmission, and sensory perception, further supporting a relationship between brain gene expression, brain mosaicism, and worker labor role. These findings demonstrate that differential brain gene expression among polymorphic workers underpins behavioral and neuroanatomical differentiation associated with complex agrarian division of labor inA. cephalotes.
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- Award ID(s):
- 1953393
- PAR ID:
- 10404103
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Comparative Neurology
- Volume:
- 531
- Issue:
- 8
- ISSN:
- 0021-9967
- Format(s):
- Medium: X Size: p. 853-865
- Size(s):
- p. 853-865
- Sponsoring Org:
- National Science Foundation
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