scholarly journals Unique allometry of group size and collective brain mass in humans and primates relative to other mammals

2019 ◽  
Author(s):  
Marcus J. Hamilton ◽  
Robert S. Walker
Keyword(s):  
Social Networks ◽  
Body Size ◽  
Group Size ◽  
Brain Size ◽  
Social Groups ◽  
Group Living ◽  
Null Model ◽  
Mammalian Brain ◽  
Brain Mass ◽  
Trade Offs

AbstractGroup living is common in mammals, particularly in primates and humans. Across species, groups are social networks where co-residing members exchange information and balance trade-offs between competition and cooperation for space, resources, and reproductive opportunities. From a macroecological perspective, species-specific group sizes are ultimately constrained by body size, population density, and the environmental supply rate of home ranges. Here, we derive an allometric null model for group size in mammals based on individual energy demands and ecological constraints. Using Bayesian phylogenetic mixed models we show that primates exhibit unique allometries relative to other mammals. Moreover, as large-bodied primates, human hunter-gatherers have among the largest social groups of any mammal. We then explore the consequences of this unique social allometry by considering how mammalian brain size scales up in social groups that differ in size across mammals. We show similarly unique allometries in what we term the collective brain mass of social groups in primates relative to all other mammals. These results show that for a given body size primates have both larger brains and larger social networks than other mammals. Consequently, proportionally larger primate brains interact in proportionally larger social networks with important consequences for group cognition. We suggest that the size, scale, and complexity of human social networks in the 21st century have deep evolutionary roots in primate ecology and mammalian brain allometry.

scholarly journals Do Different Methods Yield Equivalent Estimations of Brain Size in Birds?

2020 ◽  
Vol 95 (2) ◽  
pp. 113-122
Author(s):  
Diego Ocampo ◽  
César Sánchez ◽  
Gilbert Barrantes
Keyword(s):  
Body Size ◽  
Brain Size ◽  
Brain Mass ◽  
Wide Range ◽  
Evolutionary Studies ◽  
Relative Brain Size ◽  
Using Data ◽  
Endocranial Volume ◽  
The Brain ◽  
Size Estimates

The ratio of brain size to body size (relative brain size) is often used as a measure of relative investment in the brain in ecological and evolutionary studies on a wide range of animal groups. In birds, a variety of methods have been used to measure the brain size part of this ratio, including endocranial volume, fixed brain mass, and fresh brain mass. It is still unclear, however, whether these methods yield the same results. Using data obtained from fresh corpses and from published sources, this study shows that endocranial volume, mass of fixed brain tissue, and fresh mass provide equivalent estimations of brain size for 48 bird families, in 19 orders. We found, however, that the various methods yield significantly different brain size estimates for hummingbirds (Trochilidae). For hummingbirds, fixed brain mass tends to underestimate brain size due to reduced tissue density, whereas endocranial volume overestimates brain size because it includes a larger volume than that occupied by the brain.

scholarly journals Comparison of Dolphins' Body and Brain Measurements with Four Other Groups of Cetaceans Reveals Great Diversity

2016 ◽  
Vol 88 (3-4) ◽  
pp. 235-257 ◽  
Author(s):  
Sam H. Ridgway ◽  
Kevin P. Carlin ◽  
Kaitlin R. Van Alstyne ◽  
Alicia C. Hanson ◽  
Raymond J. Tarpley
Keyword(s):  
Body Size ◽  
Body Mass ◽  
Body Length ◽  
Brain Volume ◽  
Brain Size ◽  
The Other ◽  
Vascular Networks ◽  
Data Set ◽  
Brain Mass ◽  
Endocranial Volume

We compared mature dolphins with 4 other groupings of mature cetaceans. With a large data set, we found great brain diversity among 5 different taxonomic groupings. The dolphins in our data set ranged in body mass from about 40 to 6,750 kg and in brain mass from 0.4 to 9.3 kg. Dolphin body length ranged from 1.3 to 7.6 m. In our combined data set from the 4 other groups of cetaceans, body mass ranged from about 20 to 120,000 kg and brain mass from about 0.2 to 9.2 kg, while body length varied from 1.21 to 26.8 m. Not all cetaceans have large brains relative to their body size. A few dolphins near human body size have human-sized brains. On the other hand, the absolute brain mass of some other cetaceans is only one-sixth as large. We found that brain volume relative to body mass decreases from Delphinidae to a group of Phocoenidae and Monodontidae, to a group of other odontocetes, to Balaenopteroidea, and finally to Balaenidae. We also found the same general trend when we compared brain volume relative to body length, except that the Delphinidae and Phocoenidae-Monodontidae groups do not differ significantly. The Balaenidae have the smallest relative brain mass and the lowest cerebral cortex surface area. Brain parts also vary. Relative to body mass and to body length, dolphins also have the largest cerebellums. Cortex surface area is isometric with brain size when we exclude the Balaenidae. Our data show that the brains of Balaenidae are less convoluted than those of the other cetaceans measured. Large vascular networks inside the cranial vault may help to maintain brain temperature, and these nonbrain tissues increase in volume with body mass and with body length ranging from 8 to 65% of the endocranial volume. Because endocranial vascular networks and other adnexa, such as the tentorium cerebelli, vary so much in different species, brain size measures from endocasts of some extinct cetaceans may be overestimates. Our regression of body length on endocranial adnexa might be used for better estimates of brain volume from endocasts or from endocranial volume of living species or extinct cetaceans.

scholarly journals The Infertility Trap: The Fertility Costs of Group-Living in Mammalian Social Evolution

2021 ◽  
Vol 9 ◽  
Author(s):  
Robin I. M. Dunbar ◽  
Susanne Shultz
Keyword(s):  
Group Size ◽  
Social Evolution ◽  
Low Cost ◽  
Social Groups ◽  
Group Living ◽  
The Other ◽  
Risk Averse ◽  
Limit Group ◽  
Grouping Patterns ◽  
Environmental Demands

Mammal social groups vary considerably in size from single individuals to very large herds. In some taxa, these groups are extremely stable, with at least some individuals being members of the same group throughout their lives; in other taxa, groups are unstable, with membership changing by the day. We argue that this variability in grouping patterns reflects a tradeoff between group size as a solution to environmental demands and the costs created by stress-induced infertility (creating an infertility trap). These costs are so steep that, all else equal, they will limit group size in mammals to ∼15 individuals. A species will only be able to live in larger groups if it evolves strategies that mitigate these costs. We suggest that mammals have opted for one of two solutions. One option (fission-fusion herding) is low cost but high risk; the other (bonded social groups) is risk-averse, but costly in terms of cognitive requirements.

scholarly journals Relative brain size and cognitive equivalence in fishes

2021 ◽  
Author(s):  
Zegni Triki ◽  
Mélisande Aellen ◽  
Carel P. van Schaik ◽  
Redouan Bshary
Keyword(s):  
Body Size ◽  
Cognitive Performance ◽  
Brain Size ◽  
Regression Line ◽  
Mean Value ◽  
Mammalian Brain ◽  
Regression Slope ◽  
Scan Data ◽  
The Brain

Scientists have long struggled to establish how larger brains translate into higher cognitive performance across species. While absolute brain size often yields high predictive power of performance, its positive correlation with body size warrants some level of correction. It is expected that larger brains are needed to control larger bodies without any changes in cognitive performance. Potentially, the mean value of intraspecific brain-body slopes provides the best available estimate for an interspecific correction factor. For example, in primates, including humans, an increase in body size translates into an increase in brain size without changes in cognitive performance. Here, we provide the first evaluation of this hypothesis for another clade, teleost fishes. First, we obtained a mean intraspecific brain-body regression slope of 0.46 (albeit a relatively large range of 0.26 to 0.79) from a dataset of 51 species, with at least ten wild adult specimens per species. This mean intraspecific slope value (0.46) is similar to that of the encephalisation quotient reported for teleost (0.5), which can be used to predict mean cognitive performance in fishes. Importantly, such mean value (0.46) is much higher than in endothermic vertebrate species (~ 0.3). Second, we used wild-caught adult cleaner fish Labroides dimidiatus as a case study to test whether variation in individual cognitive performance can be explained by body size. We first obtained the brain-body regression slope for this species from two different datasets, which gave slope values of 0.58 (MRI scan data) and 0.47 (dissection data). Then, we used another dataset involving 69 adult cleaners different from those tested for their brain-body slope. We found that cognitive performance from four different tasks that estimated their learning, numerical, and inhibitory control abilities, was not significantly associated with body size. These results suggest that the intraspecific brain-body slope can estimate cognitive equivalence for this species. That is, individuals that are on the brain-body regression line are cognitively equal. While rather preliminary, our results suggest that fish and mammalian brain organisations are fundamentally different, resulting in different intra- and interspecific slopes of cognitive equivalence.

scholarly journals Trait overdispersion and the role of sociality in the assembly of social spider communities across the Americas

2018 ◽  
Vol 115 (23) ◽  
pp. 6010-6015 ◽  
Author(s):  
Philippe Fernandez-Fournier ◽  
Jennifer Guevara ◽  
Catherine Hoffman ◽  
Leticia Avilés
Keyword(s):  
Body Size ◽  
Group Size ◽  
Abiotic Factors ◽  
Social Systems ◽  
Null Model ◽  
Niche Space ◽  
Social Spider ◽  
The Social ◽  
Size And Morphology

Among the factors that may lead to differences in resource use among closely related species, body size and morphology have been traditionally considered to play a role in community assembly. Here we argue that for animals that live and forage in groups, level of sociality, reflecting differences in group size and cooperative tendencies, can be an additional and powerful dimension separating species in niche space. We compare 50+ communities of the social spider genus Anelosimus across the Americas against a null model that accounts for known effects of biotic and abiotic factors on the distribution of social systems in the genus. We show that these communities are more overdispersed than expected by chance in either or both body size and level of sociality, traits we have previously shown to be associated with differences in resource utilization (prey size, microhabitat, and phenology). We further show that the contribution of sociality to differences in the size of the prey captured is two to three times greater than that of body size, suggesting that changes in group size and cooperative tendencies may be more effective than changes in body size at separating species in niche space.

Daily Distance Traveled Is Associated with Greater Brain Size in Primates

2020 ◽  
Vol 91 (6) ◽  
pp. 654-668
Author(s):  
Marco Vidal-Cordasco ◽  
Lucía Rodríguez-González ◽  
Olalla Prado-Nóvoa ◽  
Guillermo Zorrilla-Revilla ◽  
Mario Modesto-Mata
Keyword(s):  
Group Size ◽  
Social Group ◽  
Brain Size ◽  
Ecological Factors ◽  
Primate Species ◽  
Brain Mass ◽  
Daily Movement ◽  
Size Evolution ◽  
Movement Distance ◽  
Extant Primate

Explanations for the brain size increments through primate and, particularly, human evolution are numerous. Commonly, these hypotheses rely on the influence that behavioral and ecological variables have on brain size in extant primates, such as diet quality, social group size, or home range (HR) area. However, HR area does not reflect the time spent moving. As such, it has not been properly addressed whether the effort involved in movement could have affected brain size evolution in primates. This study aimed to test the influence of daily movement on primates’ brain sizes, controlling for these other behavioral and ecological factors. We used a large comparative dataset of extant primate species and phylogenetic comparative methods. Our results show a significant correlation between daily movement and brain mass, which is not explained by the influence of diet, social group size, HR, or body mass. Hence, from an evolutionary timescale, a longer daily movement distance is not a constraining factor for the energetic investment in a larger brain. On the contrary, increased mobility could have contributed to brain mass incrementations through evolution.

scholarly journals Scaling of the Mammalian Brain: the Maternal Energy Hypothesis

Physiology ◽  
1996 ◽  
Vol 11 (4) ◽  
pp. 149-156 ◽  
Author(s):  
RD Martin
Keyword(s):  
Body Size ◽  
Metabolic Rate ◽  
Basal Metabolic Rate ◽  
Brain Size ◽  
Developing Brain ◽  
Correlation Network ◽  
Gestation Period ◽  
Mammalian Brain ◽  
Metabolic Capacity ◽  
Simple Scaling

Mammalian brain sizes have been linked to specific behavioral or physiological features because of simple scaling correlations. Examination of the correlation network for body size, brain size, basal metabolic rate, and gestation period indicates that the primary link is between maternal metabolic capacity and the developing brain of the offspring.

scholarly journals Brain size in birds is related to traffic accidents

2017 ◽  
Vol 4 (3) ◽  
pp. 161040 ◽  
Author(s):  
Anders Pape Møller ◽  
Johannes Erritzøe
Keyword(s):  
Body Size ◽  
Traffic Accidents ◽  
Moving Objects ◽  
Brain Size ◽  
Lung Mass ◽  
Liver Mass ◽  
Speed Limits ◽  
Brain Mass ◽  
The World ◽  
Heart Mass

Estimates suggest that perhaps a quarter of a billion birds are killed by traffic annually across the world. This is surprising because birds have been shown to learn speed limits. Birds have also been shown to adapt to the direction of traffic and lane use, and this apparently results in reduced risks of fatal traffic accidents. Such behavioural differences suggest that individual birds that are not killed in traffic should have larger brains for their body size. We analysed the link between being killed by traffic and relative brain mass in 3521 birds belonging to 251 species brought to a taxidermist. Birds that were killed in traffic indeed had relatively smaller brains, while there was no similar difference for liver mass, heart mass or lung mass. These findings suggest that birds learn the behaviour of car drivers, and that they use their brains to adjust behaviour in an attempt to avoid mortality caused by rapidly and predictably moving objects.

scholarly journals Living in stable social groups is associated with reduced brain size in woodpeckers ( Picidae )

2017 ◽  
Vol 13 (3) ◽  
pp. 20170008 ◽  
Author(s):  
Natalia Fedorova ◽  
Cara L. Evans ◽  
Richard W. Byrne
Keyword(s):  
Social System ◽  
Brain Size ◽  
Social Groups ◽  
Group Living ◽  
Specific Effect ◽  
Stable Pair ◽  
Pair Bonds ◽  
The Family ◽  
Cognitive Challenge ◽  
The Relationship

Group size predicts brain size in primates and some other mammal groups, but no such relationship has been found in birds. Instead, stable pair-bonding and bi-parental care have been identified as correlates of larger brains in birds. We investigated the relationship between brain size and social system within the family Picidae , using phylogenetically controlled regression analysis. We found no specific effect of duration or strength of pair-bonds, but brain sizes were systematically smaller in species living in long-lasting social groups of larger sizes. Group-living may only present a cognitive challenge in groups in which members have individually competitive relationships; we therefore propose that groups functioning for cooperative benefit may allow disinvestment in expensive brain tissue.

scholarly journals Variable fledging age according to group size: trade-offs in a cooperatively breeding bird

2007 ◽  
Vol 3 (6) ◽  
pp. 624-627 ◽  
Author(s):  
N.J Raihani ◽  
A.R Ridley
Keyword(s):  
Group Size ◽  
Group Living ◽  
Breeding Bird ◽  
Communal Roost ◽  
Trade Offs ◽  
Efficient Detection ◽  
Risk Of Predation ◽  
Cooperatively Breeding ◽  
Individual Survival ◽  
Dilution Effects

Group living can provide individuals with several benefits, including cooperative vigilance and lower predation rates. Individuals in larger groups may be less vulnerable to predation due to dilution effects, efficient detection or greater ability to repel predators. Individuals in smaller groups may consequently employ alternative behavioural tactics to compensate for their greater vulnerability to predators. Here, we describe how pied babbler ( Turdoides bicolor ) fledging age varies with group size and the associated risk of nestling predation. Nestling predation is highest in smaller groups, but there is no effect of group size on fledgling predation. Consequently, small groups fledge young earlier, thereby reducing the risk of predation. However, there is a cost to this behaviour as younger fledglings are less mobile than older fledglings: they move shorter distances and are less likely to successfully reach the communal roost tree. The optimal age to fledge young appears to depend on the trade-off between reduced nestling predation and increased fledgling mobility. We suggest that such trade-offs may be common in species where group size critically affects individual survival and reproductive success.

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