Larger animals tend to have larger brains and smaller animals tend to have smaller ones. However, some species do not fit the pattern that would be expected based on their body size. This variation between species can also apply to individual brain regions. This may be due to evolutionary forces shaping the brain when favouring particular behaviours. However, it is difficult to directly link changes in species behaviour and variations in brain structure. One way to understand the impact of evolutionary adaptations is to study species that have developed new behaviours and compare them to related ones that lack such a behaviour. An opportunity to do this lies in the ability of several species of fish to produce and sense electric fields in water. While this system is not found in most fish, it has evolved multiple times independently in distantly-related lineages. Schumacher and Carlson examined whether differences in the size of brains and individual regions between species were associated with the evolution of electric field generation and sensing. Micro-computed tomography, or μCT, scans of the brains of multiple fish species revealed that the species that can produce electricity – also known as ‘electrogenic’ species’ – have more similar brain structures to each other than to their close relatives that lack this ability. The brain regions involved in producing and detecting electrical charges were larger in these electrogenic fish. This similarity was apparent despite variations in how total brain size has evolved with body size across species. These results demonstrate how evolutionary forces acting on particular behaviours can lead to predictable changes in brain structure. Understanding how and why brains evolve will allow researchers to better predict how species’ brains and behaviours may adapt as human activities alter their environments.
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Smaller brained cliff swallows are more likely to die during harsh weather
The cognitive-buffer hypothesis proposes that more harsh and unpredictable environments favour animals with larger brains and resulting greater cognitive skills. Comparisons across taxa have supported the hypothesis, but it has rarely been tested within a species. We measured brain size, as inferred from head dimensions, for 1141 cliff swallow specimens collected in western Nebraska, 1982–2018. Cliff swallows starving to death during unusual late-spring cold snaps had significantly smaller brains than those dying from other causes, suggesting that brain size in this species can affect foraging success and that greater cognitive ability may confer advantages when conditions exceed normal environmental extremes. Brain size declined significantly with the size of the breeding colony from which a specimen came. Larger brains may be favoured in smaller colonies that represent more unpredictable and more challenging social environments where there is less public information on food sources and less collective vigilance against predators, even in relatively normal conditions. Our results provide intraspecific support for the cognitive-buffer hypothesis and emphasize the potential evolutionary impact of rare climatic events.
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- Award ID(s):
- 1930803
- PAR ID:
- 10209225
- Date Published:
- Journal Name:
- Biology Letters
- Volume:
- 16
- Issue:
- 7
- ISSN:
- 1744-9561
- Page Range / eLocation ID:
- 20200264
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Min, Byungjoon (Ed.)more » « less
The social brain hypothesis posits that species with larger brains tend to have greater social complexity. Various lines of empirical evidence have supported the social brain hypothesis, including evidence from the structure of social networks. Cooperation is a key component of group living, particularly among primates, and theoretical research has shown that particular structures of social networks foster cooperation more easily than others. Therefore, we hypothesized that species with a relatively large brain size tend to form social networks that better enable cooperation. In the present study, we combine data on brain size and social networks with theory on the evolution of cooperation on networks to test this hypothesis in non-human primates. We have found a positive effect of brain size on cooperation in social networks even after controlling for the effect of other structural properties of networks that are known to promote cooperation.
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ABSTRACT In the context of slow–fast behavioral variation, fast individuals are hypothesized to be those who prioritize speed over accuracy while slow individuals are those which do the opposite. Since energy metabolism is a critical component of neural and cognitive functioning, this predicts such differences in cognitive style to be reflected at the level of the brain. We tested this idea in honeybees by first classifying individuals into slow and fast cognitive phenotypes based on a learning assay and then measuring their brain respiration with high-resolution respirometry. Our results broadly show that inter-individual differences in cognition are reflected in differences in brain mass and accompanying energy use at the level of the brain and the whole animal. Larger brains had lower mass-specific energy usage and bees with larger brains had a higher metabolic rate. These differences in brain respiration and brain mass were, in turn, associated with cognitive differences, such that bees with larger brains were fast cognitive phenotypes whereas those with smaller brains were slow cognitive phenotypes. We discuss these results in the context of the role of energy in brain functioning and slow–fast decision making and speed accuracy trade-off.
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Explaining why animal groups vary in size is a fundamental problem in behavioral ecology. One hypothesis is that life-history differences among individuals lead to sorting of phenotypes into groups of different sizes where each individual does best. This hypothesis predicts that individuals should be relatively consistent in their use of particular group sizes across time. Little is known about whether animals’ choice of group size is repeatable across their lives, especially in long-lived species. We studied consistency in choice of breeding-colony size in colonially nesting cliff swallows ( Petrochelidon pyrrhonota ) in western Nebraska, United States, over a 32-year period, following 6,296 birds for at least four breeding seasons. Formal repeatability of size choice for the population was about 0.41. About 45% of individuals were relatively consistent in choice of colony size, while about 40% varied widely in the colony size they occupied. Birds using the smaller and larger colonies appeared more consistent in size use than birds occupying more intermediate sized colonies. Consistency in colony size was also influenced by whether a bird used the same physical colony site each year and whether the site had been fumigated to remove ectoparasites. The difference between the final and initial colony sizes for an individual, a measure of the net change in its colony size over its life, did not significantly depart from 0 for the dataset as a whole. However, different year-cohorts did show significant net change in colony size, both positive and negative, that may have reflected fluctuating selection on colony size among years based on climatic conditions. The results support phenotypic sorting as an explanation for group size variation, although cliff swallows also likely use past experience at a given site and the extent of ectoparasitism to select breeding colonies.more » « less
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Social learning is a primary mechanism for information acquisition in social species. Despite many benefits, social learning may be disadvantageous when independent learning is more efficient. For example, searching independently may be more advantageous when food sources are ephemeral and unpredictable. Individual differences in cognitive abilities can also be expected to influence social information use. Specifically, better spatial memory can make a given environment more predictable for an individual by allowing it to better track food sources. We investigated how resident food-caching chickadees discovered multiple novel food sources in both harsher, less predictable high elevation and milder, more predictable low elevation winter environments. Chickadees at high elevation were faster at discovering multiple novel food sources and discovered more food sources than birds at low elevation. While birds at both elevations used social information, the contribution of social learning to food discovery was significantly lower at high elevation. At both elevations, chickadees with better spatial cognitive flexibility were slower at discovering food sources, likely because birds with lower spatial cognitive flexibility are worse at tracking natural resources and therefore spend more time exploring. Overall, our study supported the prediction that harsh environments should favour less reliance on social learning.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1098/rsbl.2020.0264
