scholarly journals The allometry of brain size in mammals

2018 ◽  
Author(s):  
Joseph Robert Burger ◽  
Menshian Ashaki George ◽  
Claire Leadbetter ◽  
Farhin Shaikh
Keyword(s):  
Body Size ◽  
Brain Size ◽  
Phylogenetic Signal ◽  
Museum Collections ◽  
The Brain ◽  
Size Scales ◽  
Size Data ◽  
Median Slope

AbstractWhy some animals have big brains and others do not has intrigued scholars for millennia. Yet, the taxonomic scope of brain size research is limited to a few mammal lineages. Here we present a brain size dataset compiled from the literature for 1552 species with representation from 28 extant taxonomic orders. The brain-body size allometry across all mammals is (Brain) = −1.26 (Body)0.75. This relationship shows strong phylogenetic signal as expected due to shared evolutionary histories. Slopes using median species values for each order, family, and genus, to ensure evolutionary independence, approximate ∼0.75 scaling. Why brain size scales to the ¾ power to body size across mammals is, to our knowledge, unknown. Slopes within taxonomic orders exhibiting smaller size ranges are often shallower than 0.75 and range from 0.24 to 0.81 with a median slope of 0.64. Published brain size data is lacking for the majority of extant mammals (>70% of species) with strong bias in representation from Primates, Carnivores, Perrisodactyla, and Australidelphian marsupials (orders Dasyuromorphia, Diprotodontia, Peramelemorphia). Several orders are particularly underrepresented. For example, brain size data are available for less than 20% of species in each of the following speciose lineages: Soricomorpha, Rodentia, Lagomorpha, Didelphimorphia, and Scandentia. Use of museum collections can decrease the current taxonomic bias in mammal brain size data and tests of hypothesis.

Brain size/body weight in the dingo (Canis dingo): comparisons with domestic and wild canids

2017 ◽  
Vol 65 (5) ◽  
pp. 292 ◽  
Author(s):  
Bradley P. Smith ◽  
Teghan A. Lucas ◽  
Rachel M. Norris ◽  
Maciej Henneberg
Keyword(s):  
Body Size ◽  
Brain Size ◽  
Cuon Alpinus ◽  
Size Relationship ◽  
Wild Canids ◽  
Free Ranging ◽  
The Impact ◽  
Endocranial Volume ◽  
The Brain

Endocranial volume was measured in a large sample (n = 128) of free-ranging dingoes (Canis dingo) where body size was known. The brain/body size relationship in the dingoes was compared with populations of wild (Family Canidae) and domestic canids (Canis familiaris). Despite a great deal of variation among wild and domestic canids, the brain/body size of dingoes forms a tight cluster within the variation of domestic dogs. Like dogs, free-ranging dingoes have paedomorphic crania; however, dingoes have a larger brain and are more encephalised than most domestic breeds of dog. The dingo’s brain/body size relationship was similar to those of other mesopredators (medium-sized predators that typically prey on smaller animals), including the dhole (Cuon alpinus) and the coyote (Canis latrans). These findings have implications for the antiquity and classification of the dingo, as well as the impact of feralisation on brain size. At the same time, it highlights the difficulty in using brain/body size to distinguish wild and domestic canids.

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 Rethinking the Effects of Body Size on the Study of Brain Size Evolution

2019 ◽  
Vol 93 (4) ◽  
pp. 182-195 ◽  
Author(s):  
Enrique Font ◽  
Roberto García-Roa ◽  
Daniel Pincheira-Donoso ◽  
Pau Carazo
Keyword(s):  
Body Size ◽  
Brain Size ◽  
Size Variation ◽  
Brain Evolution ◽  
Scaling Effects ◽  
Selection Pressures ◽  
Body Tissues ◽  
Relative Brain Size ◽  
Functional Components ◽  
The Brain

Body size correlates with most structural and functional components of an organism’s phenotype – brain size being a prime example of allometric scaling with animal size. Therefore, comparative studies of brain evolution in vertebrates rely on controlling for the scaling effects of body size variation on brain size variation by calculating brain weight/body weight ratios. Differences in the brain size-body size relationship between taxa are usually interpreted as differences in selection acting on the brain or its components, while selection pressures acting on body size, which are among the most prevalent in nature, are rarely acknowledged, leading to conflicting and confusing conclusions. We address these problems by comparing brain-body relationships from across >1,000 species of birds and non-avian reptiles. Relative brain size in birds is often assumed to be 10 times larger than in reptiles of similar body size. We examine how differences in the specific gravity of body tissues and in body design (e.g., presence/absence of a tail or a dense shell) between these two groups can affect estimates of relative brain size. Using phylogenetic comparative analyses, we show that the gap in relative brain size between birds and reptiles has been grossly exaggerated. Our results highlight the need to take into account differences between taxa arising from selection pressures affecting body size and design, and call into question the widespread misconception that reptile brains are small and incapable of supporting sophisticated behavior and cognition.

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 A Farewell to the Encephalization Quotient: A New Brain Size Measure for Comparative Primate Cognition

2021 ◽  
pp. 1-12
Author(s):  
Carel P. van Schaik ◽  
Zegni Triki ◽  
Redouan Bshary ◽  
Sandra A. Heldstab
Keyword(s):  
Body Size ◽  
Cognitive Abilities ◽  
Brain Size ◽  
Estimation Error ◽  
Primate Species ◽  
Mammal Species ◽  
Mean Values ◽  
Encephalization Quotient ◽  
Body Sizes ◽  
Size Measure

Both absolute and relative brain sizes vary greatly among and within the major vertebrate lineages. Scientists have long debated how larger brains in primates and hominins translate into greater cognitive performance, and in particular how to control for the relationship between the noncognitive functions of the brain and body size. One solution to this problem is to establish the slope of cognitive equivalence, i.e., the line connecting organisms with an identical bauplan but different body sizes. The original approach to estimate this slope through intraspecific regressions was abandoned after it became clear that it generated slopes that were too low by an unknown margin due to estimation error. Here, we revisit this method. We control for the error problem by focusing on highly dimorphic primate species with large sample sizes and fitting a line through the mean values for adult females and males. We obtain the best estimate for the slope of circa 0.27, a value much lower than those constructed using all mammal species and close to the value expected based on the genetic correlation between brain size and body size. We also find that the estimate of cognitive brain size based on cognitive equivalence fits empirical cognitive studies better than the encephalization quotient, which should therefore be avoided in future studies on primates and presumably mammals and birds in general. The use of residuals from the line of cognitive equivalence may change conclusions concerning the cognitive abilities of extant and extinct primate species, including hominins.

scholarly journals Molecular evolutionary analysis of human primary microcephaly genes

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Nashaiman Pervaiz ◽  
Hongen Kang ◽  
Yiming Bao ◽  
Amir Ali Abbasi
Keyword(s):  
Evolutionary History ◽  
Genetic Basis ◽  
Brain Size ◽  
Primate Species ◽  
Evolutionary Analysis ◽  
Australopithecus Afarensis ◽  
Primary Microcephaly ◽  
Modern Humans ◽  
History Of ◽  
The Brain

Abstract Background There has been a rapid increase in the brain size relative to body size during mammalian evolutionary history. In particular, the enlarged and globular brain is the most distinctive anatomical feature of modern humans that set us apart from other extinct and extant primate species. Genetic basis of large brain size in modern humans has largely remained enigmatic. Genes associated with the pathological reduction of brain size (primary microcephaly-MCPH) have the characteristics and functions to be considered ideal candidates to unravel the genetic basis of evolutionary enlargement of human brain size. For instance, the brain size of microcephaly patients is similar to the brain size of Pan troglodyte and the very early hominids like the Sahelanthropus tchadensis and Australopithecus afarensis. Results The present study investigates the molecular evolutionary history of subset of autosomal recessive primary microcephaly (MCPH) genes; CEP135, ZNF335, PHC1, SASS6, CDK6, MFSD2A, CIT, and KIF14 across 48 mammalian species. Codon based substitutions site analysis indicated that ZNF335, SASS6, CIT, and KIF14 have experienced positive selection in eutherian evolutionary history. Estimation of divergent selection pressure revealed that almost all of the MCPH genes analyzed in the present study have maintained their functions throughout the history of placental mammals. Contrary to our expectations, human-specific adoptive evolution was not detected for any of the MCPH genes analyzed in the present study. Conclusion Based on these data it can be inferred that protein-coding sequence of MCPH genes might not be the sole determinant of increase in relative brain size during primate evolutionary history.

scholarly journals Effects of Brain Size on Adult Neurogenesis in Shrews

2021 ◽  
Vol 22 (14) ◽  
pp. 7664
Author(s):  
Katarzyna Bartkowska ◽  
Krzysztof Turlejski ◽  
Beata Tepper ◽  
Leszek Rychlik ◽  
Peter Vogel ◽  
...  
Keyword(s):  
Adult Neurogenesis ◽  
Subventricular Zone ◽  
Molecular Mechanisms ◽  
Brain Size ◽  
Hippocampal Formation ◽  
Small Animals ◽  
Suncus Murinus ◽  
The Brain ◽  
Neomys Fodiens ◽  
Migratory Stream

Shrews are small animals found in many different habitats. Like other mammals, adult neurogenesis occurs in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus (DG) of the hippocampal formation. We asked whether the number of new generated cells in shrews depends on their brain size. We examined Crocidura russula and Neomys fodiens, weighing 10–22 g, and Crocidura olivieri and Suncus murinus that weigh three times more. We found that the density of proliferated cells in the SVZ was approximately at the same level in all species. These cells migrated from the SVZ through the rostral migratory stream to the olfactory bulb (OB). In this pathway, a low level of neurogenesis occurred in C. olivieri compared to three other species of shrews. In the DG, the rate of adult neurogenesis was regulated differently. Specifically, the lowest density of newly generated neurons was observed in C. russula, which had a substantial number of new neurons in the OB compared with C. olivieri. We suggest that the number of newly generated neurons in an adult shrew’s brain is independent of the brain size, and molecular mechanisms of neurogenesis appeared to be different in two neurogenic structures.

On the anatomic relation of choroid plexus to brain: a comparative study

1980 ◽  
Vol 238 (1) ◽  
pp. R76-R81 ◽  
Author(s):  
H. F. Cserr ◽  
M. Bundgaard ◽  
J. K. Ashby ◽  
M. Murray
Keyword(s):  
Choroid Plexus ◽  
Brain Volume ◽  
Brain Size ◽  
Ventricular Volume ◽  
Brain Weight ◽  
Air Breathing ◽  
Original Proposal ◽  
Adaptive Value ◽  
Choroid Plexuses ◽  
The Brain

The size of choroid plexuses and cerebral ventricles relative to brain varies widely among vertebrates. The functional significance of this variability has attracted little attention since Herrick's original proposal that large choroid plexuses might enhance oxygen delivery to the brain and therefore be of adaptive value in the transition of vertebrates from water to air breathing. We compared choroid plexus and brain weight or ventricular and brain volume in 40 species from nine vertebrate groups. Both choroid plexus weight and ventricular volume were unrelated to brain size. Plexus weight ranged from 0 to 5.2% of brain weight and ventricular volume from 0.9 to 132% of brain volume. Amid this diversity the dipnoans, chondrosteans, holosteans, amphibians, and crossopterygian examined in this study are exceptional in uniformly having large plexuses. The adaptive significance of large choroid plexuses may lie in the presence of specific homeostatic mechanisms and their role in the response to the increases in PCO2 that accompany the transition to air breathing.

Body size, brain size, and sexual dimorphism in Homo naledi from the Dinaledi Chamber

2017 ◽  
Vol 111 ◽  
pp. 119-138 ◽  
Author(s):  
Heather M. Garvin ◽  
Marina C. Elliott ◽  
Lucas K. Delezene ◽  
John Hawks ◽  
Steven E. Churchill ◽  
...  
Keyword(s):  
Body Size ◽  
Sexual Dimorphism ◽  
Brain Size

Longitudinal Brain Size Measurements in App/Ps1 Transgenic Mice

2010 ◽  
Vol 4 ◽  
pp. MRI.S5885 ◽  
Author(s):  
Trevor J. Vincent ◽  
Jonathan D. Thiessen ◽  
Laryssa M. Kurjewicz ◽  
Shelley L. Germscheid ◽  
Allan J. Turner ◽  
...  
Keyword(s):  
Brain Size ◽  
Three Dimensional ◽  
Gene Mutations ◽  
Mutant Form ◽  
Swedish Mutation ◽  
Significant Difference ◽  
Lateral Width ◽  
Resolution Imaging ◽  
Or Gene ◽  
The Brain

There appear to be species differences among the effects of gene mutations related to familial Alzheimer's disease on the brain during aging. To gain a better understanding of the effects of the Swedish mutation of amyloid precursor protein and the mutant form of human presenilin 1 on mice, commercially available mice from Jackson Laboratory were studied. Three dimensional T2*-weighted imaging was used to monitor the size of brains of APP/PS1 mice monthly, from 6 to 13 months of age. No significant difference was measured in the size of the medial-lateral width, dorsal-ventral height, rostral-caudal length or the volume of the APPSwe/ PS1 mouse brain. Faster and higher-resolution imaging methods are needed to accurately determine if small volume or shape changes occur in mouse brains with age or gene mutations.

Sign in / Sign up

Export Citation Format

Share Document