scholarly journals The Evolution of Relative Brain Size in Marsupials Is Energetically Constrained but Not Driven by Behavioral Complexity

2015 ◽  
Vol 85 (2) ◽  
pp. 125-135 ◽  
Author(s):  
Vera Weisbecker ◽  
Simon Blomberg ◽  
Anne W. Goldizen ◽  
Meredeth Brown ◽  
Diana Fisher
Keyword(s):  
Social Complexity ◽  
Brain Size ◽  
Maternal Investment ◽  
Generalized Least Squares ◽  
Brain Morphology ◽  
Mammalian Brain ◽  
Data Set ◽  
Behavioral Complexity ◽  
Size Evolution ◽  
Relative Brain Size

Evolutionary increases in mammalian brain size relative to body size are energetically costly but are also thought to confer selective advantages by permitting the evolution of cognitively complex behaviors. However, many suggested associations between brain size and specific behaviors - particularly related to social complexity - are possibly confounded by the reproductive diversity of placental mammals, whose brain size evolution is the most frequently studied. Based on a phylogenetic generalized least squares analysis of a data set on the reproductively homogenous clade of marsupials, we provide the first quantitative comparison of two hypotheses based on energetic constraints (maternal investment and seasonality) with two hypotheses that posit behavioral selection on relative brain size (social complexity and environmental interactions). We show that the two behavioral hypotheses have far less support than the constraint hypotheses. The only unambiguous associates of brain size are the constraint variables of litter size and seasonality. We also found no association between brain size and specific behavioral complexity categories within kangaroos, dasyurids, and possums. The largest-brained marsupials after phylogenetic correction are from low-seasonality New Guinea, supporting the notion that low seasonality represents greater nutrition safety for brain maintenance. Alternatively, low seasonality might improve the maternal support of offspring brain growth. The lack of behavioral brain size associates, found here and elsewhere, supports the general ‘cognitive buffer hypothesis' as the best explanatory framework of mammalian brain size evolution. However, it is possible that brain size alone simply does not provide sufficient resolution on the question of how brain morphology and cognitive capacities coevolve.

scholarly journals Testing hypotheses of marsupial brain size variation using phylogenetic multiple imputations and a Bayesian comparative framework

2021 ◽  
Vol 288 (1947) ◽  
Author(s):  
Orlin S. Todorov ◽  
Simone P. Blomberg ◽  
Anjali Goswami ◽  
Karen Sears ◽  
Patrik Drhlík ◽  
...  
Keyword(s):  
Litter Size ◽  
Brain Size ◽  
Size Variation ◽  
Reproductive Traits ◽  
Mammalian Brain ◽  
Gestation Length ◽  
High Coverage ◽  
Ecological Predictors ◽  
Size Evolution ◽  
Relative Brain Size

Considerable controversy exists about which hypotheses and variables best explain mammalian brain size variation. We use a new, high-coverage dataset of marsupial brain and body sizes, and the first phylogenetically imputed full datasets of 16 predictor variables, to model the prevalent hypotheses explaining brain size evolution using phylogenetically corrected Bayesian generalized linear mixed-effects modelling. Despite this comprehensive analysis, litter size emerges as the only significant predictor. Marsupials differ from the more frequently studied placentals in displaying a much lower diversity of reproductive traits, which are known to interact extensively with many behavioural and ecological predictors of brain size. Our results therefore suggest that studies of relative brain size evolution in placental mammals may require targeted co-analysis or adjustment of reproductive parameters like litter size, weaning age or gestation length. This supports suggestions that significant associations between behavioural or ecological variables with relative brain size may be due to a confounding influence of the extensive reproductive diversity of placental mammals.

scholarly journals Testing hypotheses of marsupial brain size variation using phylogenetic multiple imputations and a Bayesian comparative framework

2021 ◽  
Author(s):  
Orlin S. Todorov ◽  
Simone P. Blomberg ◽  
Anjali Goswami ◽  
Karen Sears ◽  
Patrik Drhlík ◽  
...  
Keyword(s):  
Litter Size ◽  
Brain Size ◽  
Size Variation ◽  
Reproductive Traits ◽  
Mammalian Brain ◽  
Gestation Length ◽  
High Coverage ◽  
Ecological Predictors ◽  
Size Evolution ◽  
Relative Brain Size

AbstractConsiderable controversy exists about which hypotheses and variables best explain mammalian brain size variation. We use a new, high-coverage dataset of marsupial brain and body sizes, and the first phylogenetically imputed full datasets of 16 predictor variables, to model the prevalent hypotheses explaining brain size evolution using phylogenetically corrected Bayesian generalised linear mixed-effects modelling. Despite this comprehensive analysis, litter size emerges as the only significant predictor. Marsupials differ from the more frequently studied placentals in displaying much lower diversity of reproductive traits, which are known to interact extensively with many behavioural and ecological predictors of brain size. Our results therefore suggest that studies of relative brain size evolution in placental mammals may require targeted co-analysis or adjustment of reproductive parameters like litter size, weaning age, or gestation length. This supports suggestions that significant associations between behavioural or ecological variables with relative brain size may be due to a confounding influence of the extensive reproductive diversity of placental mammals.

Brain size evolution in small mammals: test of the expensive tissue hypothesis

Mammalia ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ying Jiang ◽  
Jia Yu Wang ◽  
Xiao Fu Huang ◽  
Chun Lan Mai ◽  
Wen Bo Liao
Keyword(s):  
Small Mammals ◽  
Brain Size ◽  
Reproductive Investment ◽  
Generalized Least Squares ◽  
Offspring Number ◽  
Size Evolution ◽  
Large Brain ◽  
Species Evolution ◽  
The Cost ◽  
Expensive Tissue Hypothesis

Abstract Brain size exhibits significant changes within and between species. Evolution of large brains can be explained by the need to improve cognitive ability for processing more information in changing environments. However, brains are among the most energetically expensive organs. Enlarged brains can impose energetic demands that limit brain size evolution. The expensive tissue hypothesis (ETH) states that a decrease in the size of another expensive tissue, such as the gut, should compensate for the cost of a large brain. We studied the interplay between energetic limitations and brain size evolution in small mammals using phylogenetically generalized least squares (PGLS) regression analysis. Brain mass was not correlated with the length of the digestive tract in 37 species of small mammals after correcting for phylogenetic relationships and body size effects. We further found that the evolution of a large brain was not accompanied by a decrease in male reproductive investments into testes mass and in female reproductive investment into offspring number. The evolution of brain size in small mammals is inconsistent with the prediction of the ETH.

scholarly journals Does more maternal investment mean a larger brain? Evolutionary relationships between reproductive mode and brain size in chondrichthyans

2011 ◽  
Vol 62 (6) ◽  
pp. 567 ◽  
Author(s):  
Christopher G. Mull ◽  
Kara E. Yopak ◽  
Nicholas K. Dulvy
Keyword(s):  
Least Squares ◽  
Body Mass ◽  
Brain Size ◽  
Maternal Investment ◽  
Branch Length ◽  
Reproductive Mode ◽  
Ordinary Least Squares ◽  
Egg Laying ◽  
Wide Range ◽  
Relative Brain Size

Chondrichthyans have the most diverse array of reproductive strategies of any vertebrate group, ranging from egg-laying to live-bearing with placental matrotrophy. Matrotrophy is defined as additional maternal provisioning beyond the yolk to the developing neonate; in chondrichthyans, this occurs through a range of mechanisms including uterine milk, oophagy, uterine cannibalism and placentotrophy. Chondrichthyans also exhibit a wide range of relative brain sizes and highly diverse patterns of brain organisation. Brains are energetically expensive to produce and maintain, and represent a major energetic constraint during early life in vertebrates. In mammals, more direct maternal–fetal placental connections have been associated with larger brains (steeper brain–body allometric scaling relationships). We test for a relationship between reproductive mode and relative brain size across 85 species from six major orders of chondrichthyans by using several phylogenetic comparative analyses. Ordinary least-squares (OLS) and reduced major axis (RMA) regression of body mass versus brain mass suggest that increased maternal investment results in a larger relative brain size. Our findings were supported by phylogenetic generalised least-squares models (pGLS), which also highlighted that these results vary with evolutionary tempo, as described by different branch-length assumptions. Across all analyses, maximum body size had a significant influence on the relative brain size, with large-bodied species (body mass >100 kg) having relatively smaller brains. The present study suggests that there may be a link between reproductive investment and relative brain size in chondrichthyans; however, a more definitive test requires a better-resolved phylogeny and a more nuanced categorisation of the level of maternal investment in chondrichthyans.

scholarly journals Population densities predict forebrain size variation in the cleaner fish Labroides dimidiatus

2019 ◽  
Vol 286 (1915) ◽  
pp. 20192108 ◽  
Author(s):  
Zegni Triki ◽  
Elena Levorato ◽  
William McNeely ◽  
Justin Marshall ◽  
Redouan Bshary
Keyword(s):  
Cognitive Processing ◽  
Social Complexity ◽  
Brain Size ◽  
Local Density ◽  
Size Variation ◽  
Causal Link ◽  
Brain Morphology ◽  
Cleaner Fish ◽  
Labroides Dimidiatus ◽  
Brain Parts

The ‘social brain hypothesis' proposes a causal link between social complexity and either brain size or the size of key brain parts known to be involved in cognitive processing and decision-making. While previous work has focused on comparisons between species, how social complexity affects plasticity in brain morphology at the intraspecific level remains mostly unexplored. A suitable study model is the mutualist ‘cleaner’ fish Labroides dimidiatus , a species that removes ectoparasites from a variety of ‘client’ fishes in iterative social interactions. Here, we report a positive relationship between the local density of cleaners, as a proxy of both intra- and interspecific sociality, and the size of the cleaner's brain parts suggested to be associated with cognitive functions, such as the diencephalon and telencephalon (that together form the forebrain). In contrast, the size of the mesencephalon, rhombencephalon, and brain stem, assumed more basal in function, were independent of local fish densities. Selective enlargement of brain parts, that is mosaic brain adjustment, appears to be driven by population density in cleaner fish.

scholarly journals Neurodevelopmental LincRNA Microsyteny Conservation and Mammalian Brain Size Evolution

PLoS ONE ◽  
2015 ◽  
Vol 10 (7) ◽  
pp. e0131818 ◽  
Author(s):  
Eric Lewitus ◽  
Wieland B. Huttner
Keyword(s):  
Brain Size ◽  
Mammalian Brain ◽  
Size Evolution

scholarly journals No association between brain size and male sexual behavior in the guppy

2015 ◽  
Vol 61 (2) ◽  
pp. 265-273 ◽  
Author(s):  
Alberto Corral-López ◽  
Simon Eckerström-Liedholm ◽  
Wouter VAN Der Bijl ◽  
Alexander Kotrschal ◽  
Niclas Kolm
Keyword(s):  
Sexual Behavior ◽  
Animal Behavior ◽  
Sexual Behaviors ◽  
Brain Size ◽  
Experimental Studies ◽  
Brain Morphology ◽  
Female Behavior ◽  
Male Sexual Behavior ◽  
Potential Association ◽  
Relative Brain Size

Abstract Animal behavior is remarkably variable at all taxonomic levels. Over the last decades, research on animal behavior has focused on understanding ultimate processes. Yet, it has progressively become more evident that to fully understand behavioral variation, ultimate explanations need to be complemented with proximate ones. In particular, the mechanisms generating variation in sexual behavior remain an open question. Variation in aspects of brain morphology has been suggested as a plausible mechanism underlying this variation. However, our knowledge of this potential association is based almost exclusively on comparative analyses. Experimental studies are needed to establish causality and bridge the gap between microand macroevolutionary mechanisms concerning the link between brain and sexual behavior. We used male guppies that had been artificially selected for large or small relative brain size to study this association. We paired males with females and scored the full known set of male and female sexual behaviors described in guppies. We found several previously demonstrated associations between male traits, male behavior and female behavior. Females responded more strongly towards males that courted more and males with more orange coloration. Also, larger males and males with less conspicuous coloration attempted more coerced copulations. However, courting, frequency of coerced copulation attempts, total intensity of sexual behavior, and female response did not differ between largeand small-brained males. Our data suggest that relative brain size is an unlikely mechanism underlying variation in sexual behavior of the male guppy. We discuss these findings in the context of the conditions under which relative brain size might affect male sexual behavior.

Genome size and brain cell density in birds

2018 ◽  
Vol 96 (4) ◽  
pp. 379-382
Author(s):  
T. Ryan Gregory
Keyword(s):  
Body Size ◽  
Genome Size ◽  
Brain Size ◽  
Brain Cell ◽  
Small Cells ◽  
Nucleus Size ◽  
Data Set ◽  
Cell Numbers ◽  
Avian Flight ◽  
Relative Brain Size

Birds exhibit small, constrained genome sizes relative to many other vertebrates. This has often been attributed to the metabolic constraints of powered flight, which requires small cells for efficient gas exchange. Small cells, in turn, are achieved in part by limiting nucleus size and thus DNA content. However, metabolism is not the only organismal trait that correlates with genome size in birds; relationships have also been reported with body size (positive) and relative brain size (inverse). In this study, a recent data set on cell numbers in the brains of birds was combined with available data on genome sizes to demonstrate a relationship between genome size and density of cells per gram of brain tissue. This suggests that small genomes are relevant not only in the evolution of avian flight but may also be associated with the extraordinary behavioural complexity shown by birds.

No evidence for the expensive-tissue hypothesis in Fejervarya limnocharis

2018 ◽  
Vol 68 (3) ◽  
pp. 265-276 ◽  
Author(s):  
Sheng Nan Yang ◽  
Hao Feng ◽  
Long Jin ◽  
Zhao Min Zhou ◽  
Wen Bo Liao
Keyword(s):  
Brain Size ◽  
Relative Size ◽  
Trade Offs ◽  
Size Evolution ◽  
Large Brain ◽  
Relative Brain Size ◽  
The Cost ◽  
Kidney Liver ◽  
Expensive Tissue Hypothesis ◽  
Fejervarya Limnocharis

AbstractBecause the brain is one of the energetically most expensive organs of animals, trade-offs have been hypothesized to exert constraints on brain size evolution. The expensive-tissue hypothesis predicts that the cost of a large brain should be compensated by decreasing size of other metabolically costly tissues, such as the gut. Here, we analyzed the relationships between relative brain size and the size of other metabolically costly tissues (i.e., gut, heart, lung, kidney, liver, spleen or limb muscles) among four Fejervarya limnocharis populations to test the predictions of the expensive-tissue hypothesis. We did not find that relative brain size was negatively correlated with relative gut length after controlling for body size, which was inconsistent with the prediction of the expensive-tissue hypothesis. We also did not find negative correlations between relative brain mass and relative size of the other energetically expensive organs. Our findings suggest that the cost of large brains in F. limnocharis cannot be compensated by decreasing size in other metabolically costly tissues.

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