Dolphin genome provides evidence for adaptive evolution of nervous system genes and a molecular rate slowdown

McGowen, Michael R.; Grossman, Lawrence I.; Wildman, Derek E.

doi:10.1098/rspb.2012.0869

Cited by 85 publications

(92 citation statements)

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“…For example, two brains with similar neurophysiologic characteristics, i.e., a similar number of neurons and neural connectivity, may exhibit substantial differences in the number of computations they are able to perform per unit of time as a result of differences in the metabolic turnover of their brains. This fact is particularly interesting, especially when taking into consideration that bottlenose dolphins (and other cetaceans) have a higher basal metabolic rate than terrestrial mammals of the same size and they consume oxygen at a rate that is greater than that documented for both humans and elephants [65,108,109].…”

Section: Discussionmentioning

confidence: 99%

“…Thus, it is plausible to hypothesize that a faster synaptic transmission speed is possible in the cerebral cortex of cetaceans compared to terrestrial mammals as their metabolism may have evolved to rely more on anaerobic glucose metabolism, especially during periods of increased energy requirements and/or under oxygen deprived conditions (i.e., diving conditions) [121]. For example, the dolphin lineage showed positive for the inheritance of genes involved in the metabolism of glucose and lipids, as well as faster rates of evolution in genes expressed in the mitochondria, both of which indicate an evolution in energy metabolism [65]. Further arguments supporting this perspective come from the work of Williams et al [122] who studied the physiology of the bottlenose dolphin during exercise (i.e., animals either pushing against a load cell or swimming next to a boat).…”

Section: Discussionmentioning

confidence: 99%

“…In general, cetaceans possess large brains when compared to terrestrial mammals, both in absolute and relative terms. Their brains also have much lower neuronal density, but at the same time, higher ratios of glial cells to neurons, and greater proportion of cortical white matter versus gray matter [2,17,65]. Furthermore, one of the most fascinating characteristics of their brains is the high degree of cortical gyrification and the resulting neocortical surface area.…”

Section: Implications For Cetacean Cognitionmentioning

confidence: 99%

“…In addition, it supports the belief that brain size cannot be increased indefinitely due to metabolic considerations. For example, from an evolutionary neuroscience perspective several studies have correlated increases in relative brain size with changes in diet, size of other organs, or neural rate of energy consumption to make those large brains possible [9,13,65].…”

Section: The Limiting Factors Of Intelligence: Neuron Numbers and Enementioning

confidence: 99%

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Is Cetacean Intelligence Special? New Perspectives on the Debate

Chinea

2017

Entropy

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Abstract:In recent years, the interpretation of our observations of animal behaviour, in particular that of cetaceans, has captured a substantial amount of attention in the scientific community. The traditional view that supports a special intellectual status for this mammalian order has fallen under significant scrutiny, in large part due to problems of how to define and test the cognitive performance of animals. This paper presents evidence supporting complex cognition in cetaceans obtained using the recently developed intelligence and embodiment hypothesis. This hypothesis is based on evolutionary neuroscience and postulates the existence of a common information-processing principle associated with nervous systems that evolved naturally and serves as the foundation from which intelligence can emerge. This theoretical framework explaining animal intelligence in neural computational terms is supported using a new mathematical model. Two pathways leading to higher levels of intelligence in animals are identified, each reflecting a trade-off either in energetic requirements or the number of neurons used. A description of the evolutionary pathway that led to increased cognitive capacities in cetacean brains is detailed and evidence supporting complex cognition in cetaceans is presented. This paper also provides an interpretation of the adaptive function of cetacean neuronal traits.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Implications For Cetacean Cognitionmentioning

confidence: 99%

Section: The Limiting Factors Of Intelligence: Neuron Numbers and Enementioning

confidence: 99%

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Is Cetacean Intelligence Special? New Perspectives on the Debate

Chinea

2017

Entropy

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“…The apparent elevation in dN/dS is likely to be influenced by the low number of substitutions on short branches. This problem is particularly strong for cetaceans, which have low substitution rates [4]. Second, it is suggested that positive selection is limited to mammalian orders with high EQs.…”

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confidence: 99%

ASPM and mammalian brain evolution: a case study in the difficulty in making macroevolutionary inferences about gene–phenotype associations

2014

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Identifying the genetic basis of adaptive phenotypes can be a significant step towards understanding how that phenotype evolved. With the increased availability of interspecific molecular data, an approach to uncover such genes has been to search for signatures of adaptive evolution at the molecular level. Many analyses have adopted a candidate gene approach, focusing on genes with important developmental roles. One such candidate gene is ASPM, which is involved in neurogenesis and associated with major neurological disorders [1]. The molecular evolution of ASPM has been investigated for a decade (see electronic supplementary material, table S1), under the hypothesis that it contributes to primate brain evolution. A recent study by Xu et al.[2] extends the taxonomic scope by demonstrating that ASPM evolved adaptively in cetaceans. However, descriptive studies of patterns of selection are now being supplanted by those that explicitly test for gene -phenotype associations. Using such an approach, we find that Xu et al.'s conclusion that ASPM is linked to increases in cetacean encephalization quotient (EQ), a measure of relative brain size, is not supported. We highlight developments in the analysis of molecular data and phylogenetic methods that are capable of resolving major issues in functional gene -phenotype coevolution, which we hope will provoke discussion and aid future studies.One approach for making gene -phenotype associations is to test for shifts in selection pressure acting on a gene in taxa that display the phenotype of interest. This frequently involves comparing estimates of dN/dS, a measure of the strength of selection acting on a protein-coding gene, using a range of tests implemented in software such as PAML (see electronic supplementary material, table S2) [3]. The results of these tests can be influenced by the nature of the data and, in particular, require sufficient evolutionary variation to make reliable estimates. Data with few substitutions or from a restricted number of taxa can lead to spurious results. These effects may be evident in Xu et al.'s analysis [2]. First, they suggest that a high proportion of branches in the cetacean phylogeny have an elevated dN/dS, which they interpret as evidence of increased positive selection, but do not perform explicit tests of this hypothesis. Further analysis (see the electronic supplementary material) suggests that none of these values are significantly greater than one, the threshold for accepting adaptive evolution. The apparent elevation in dN/dS is likely to be influenced by the low number of substitutions on short branches. This problem is particularly strong for cetaceans, which have low substitution rates [4]. Second, it is suggested that positive selection is limited to mammalian orders with high EQs. However, this result is likely to be influenced by sampling bias, and inclusion of further taxa provides evidence for positive selection across mammals (see the electronic supplementary material). Identifying robust shifts in selection pressur...

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Gene Evolution and Human Adaptation

Harris

2013

Encyclopedia of Life Sciences

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Dolphin genome provides evidence for adaptive evolution of nervous system genes and a molecular rate slowdown

Cited by 85 publications

References 73 publications

Is Cetacean Intelligence Special? New Perspectives on the Debate

Is Cetacean Intelligence Special? New Perspectives on the Debate

ASPM and mammalian brain evolution: a case study in the difficulty in making macroevolutionary inferences about gene–phenotype associations

Gene Evolution and Human Adaptation

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