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R A Barton

Publications and source records attributed to R A Barton.

17 recordsLinked to original sources
PubMed2000

Mosaic evolution of brain structure in mammals.

The mammalian brain comprises a number of functionally distinct systems. It might therefore be expected that natural selection on particular behavioural capacities would have caused size changes selectively, in the systems mediating those capacities. It has been claimed, however, that developmental constraints limited such mosaic evolution, causing co-ordinated size change among individual brain components. Here we analyse comparative data to demonstrate that mosaic change has been an important factor in brain structure evolution. First, the neocortex shows about a fivefold difference in volume between primates and insectivores even after accounting for its scaling relationship with the rest of the brain. Second, brain structures with major anatomical and functional links evolved together independently of evolutionary change in other structures. This is true at the level of both basic brain subdivisions and more fine-grained functional systems. Hence, brain evolution in these groups involved complex relationships among individual brain components.

Animals↗
PubMed1998

Visual specialization and brain evolution in primates.

Several theories have been proposed to explain the evolution of species differences in brain size, but no consensus has emerged. One unresolved question is whether brain size differences are a result of neural specializations or of biological constraints affecting the whole brain. Here I show that, among primates, brain size variation is associated with visual specialization. Primates with large brains for their body size have relatively expanded visual brain areas, including the primary visual cortex and lateral geniculate nucleus. Within the visual system, it is, in particular, one functionally specialized pathway upon which selection has acted: evolutionary changes in the number of neurons in parvocellular, but not magnocellular, layers of the lateral geniculate nucleus are correlated with changes in both brain size and ecological variables (diet and social group size). Given the known functions of the parvocellular pathway, these results suggest that the relatively large brains of frugivorous species are products of selection on the ability to perceive and select fruits using specific visual cues such as colour. The separate correlation between group size and visual brain evolution, on the other hand, may indicate the visual basis of social information processing in the primate brain.

Animals↗
PubMed1996

Neocortex size and behavioural ecology in primates.

The neocortex is widely held to have been the focus of mammalian brain evolution, but what selection pressures explain the observed diversity in its size and structure? Among primates, comparative studies suggest that neocortical evolution is related to the cognitive demands of sociality, and here I confirm that neocortex size and social group size are positively correlated once phylogenetic associations and overall brain size are taken into account. This association holds within haplorhine but not strepsirhine primates. In addition, the neocortex is larger in diurnal than in nocturnal primates, and among diurnal haplorhines its size is positively correlated with the degree of frugivory. These ecological correlates reflect the diverse sensory-cognitive functions of the neocortex.

Animals↗
PubMed1995

Evolutionary radiation of visual and olfactory brain systems in primates, bats and insectivores.

How brains have evolved in response to particular selection pressures is illuminated by ecological correlates of differences in brain structure among contemporary species. The focus of most comparative studies has been on the overall size of brains relative to body size, hence ignoring the ways in which selection operates on specific neural systems. Here we investigate evolutionary radiations in the size of visual and olfactory brain structures within three orders of mammals: primates, bats and insectivores. The comparative relationships within these three orders show both similarities and differences. After removal of the allometric effect of overall brain size, the sizes of different structures within each sensory modality are positively correlated in all three orders. Correlations between visual and olfactory structures, however, are negative in primates, negative but non-significant in insectivores, and positive in bats. In both primates and insectivores, nocturnal lineages tend to have larger olfactory structures than do diurnal or partly diurnal lineages, and among the primates diurnal lineages have larger striate visual cortexes. Hence the apparent trade-off between vision and olfaction in primates seems to be related to the divergence of nocturnal and diurnal forms. However, negative correlations between visual and olfactory structures were also found when nocturnal strepsirhines and diurnal haplorhines were analysed separately, suggesting that ecological variables in addition to activity timing may be significant. Indeed, there were also associations with diet: frugivory was associated with enlargements of the geniculostriate visual system in diurnal primates, enlargements of olfactory structures in nocturnal primates, and possibly enlargements of both in bats. Further ecological associations were found within insectivores: aquatic lineages had smaller olfactory structures than in their non-aquatic counterparts, and fossorial lineages had smaller optic nerves than in non-fossorial forms. We conclude that activity timing, diet and habitat have each played a role in the evolutionary radiation of mammalian sensory systems, but with varying effects in the different taxa. Some of the associations between ecology and sensory systems suggest alternative explanations for correlates of overall brain size, which have in the past commonly been interpreted in terms of selection on intelligence.

Adaptation, Biological↗
PubMed1993

Comparative evidence indicating neural specialization for predatory behaviour in mammals.

The evolution of cognitive and sensory specializations must involve concomitant modifications of neural substrates. Ecological correlates of species differences in brain structure are intriguing sources of evidence about such evolutionary specialization but, to date, these have been identified only for gross parameters, such as overall brain size and the size of major brain regions. Here we show that a behavioural specialization in mammals, predation, is associated with species differences in the fine structure of a single neural pathway, the tectospinal tract. Both the relative number of neurons in this pathway and the relative size of their cell bodies were greater in more predatory species than in their less predatory counterparts within each of four separate mammalian orders. Expansion of these analyses to consider comparisons between taxa at a variety of taxonomic levels gave further support to the idea of a relation between predatory habits and the evolution of the tectospinal tract. In addition, within the primates, the number of neurons in the tectospinal tract was significantly correlated with the proportion of prey in the diet. These results therefore appear to provide an example of correlated evolution between a specific neural system and behaviour which applies generally within the mammals. They also help to unify findings from physiological and anatomical studies on a wider range of vertebrate taxa, including reptiles and amphibians.

Adaptation, Physiological↗
PubMed1993

Chemical composition of baboon plant foods: implications for the interpretation of intra- and interspecific differences in diet.

Information on the chemical composition of baboon foods from the Laikipia Plateau, Kenya, is presented. Despite some differences in methods, results of analyses performed on the same foods at different sites were found to be extremely consistent, encouraging the view that meaningful intra- and interspecific comparisons of diet selection are feasible. Contrary to assumptions in the literature, no relationship between the abundance of food types and their chemical composition was found, nor was the foliage eaten by the baboons found to be a low-quality or high-fibre item in comparison with fruits and storage organs. Emphasis is placed on the need for caution in the use of simplistic dietary taxonomies which imply phytochemical and ecological homogeneity within broad food categories. Comparisons between three species revealed marked differences in the chemical composition of their diets; in particular, baboon diets were found to be higher in protein and lower in fibre than those of either lowland gorillas or Malaysian leaf monkeys, and differences in condensed tannin levels were also found. The relationship between these differences and the socio-ecology of the three species is discussed.

Alkaloids↗
PubMed1991

Dietary and foraging strategies of baboons.

As large-bodied savannah primates, baboons have long been of special interest to students of human evolution: many different populations have been studied and dietary comparisons among them are becoming possible. Baboons' foraging strategies can be shown to combine high degrees of flexibility and breadth with selectivity. In this paper we develop and test multivariate models of the basis of diet selection for populations of montane and savannah baboons. Food selection is positively related to protein and lipid content and negatively to fibre, phenolics and alkaloids. Seasonal changes in dietary criteria predicted by these rules are tested and confirmed. Although nutritional bottlenecks occur at intervals, a comparison between long-term nutrient intakes in four different populations indicates convergence on lower degrees of variation than exist in superficial foodstuff profiles.

Acclimatization↗
PubMed1979

Mutagenicity of the non-carcinogenic dibenzylnitrosamine and an alpha-acetoxy derivative.

The mutagenicity of a non-carcinogenic nitrosamine, N,N-dibenzylnitrosamine (I), and a chemically synthesized alpha-acetoxy derivative, N-(alpha-acetoxy-benzyl)-N-benzylnitrosamine (II), has been examined in Salmonella typhimurium TA100 and TA1535. Compound (I) was non-mutagenic when tested directly or in the presence of a metabolic activation system while (II) was highly mutagenic when tested directly. This is the first report on the conversion of a non-mutagenic N-nitrosamine to a mutagen by the formation of an alpha-acetoxy derivative.

Animals↗
PubMed1979

Nicotinamide adenine dinucleotide metabolism in Candida albicans.

The functional pathways of nicotinamide adenine dinucleotide (NAD) biosynthesis and their regulation were studied in the dimorphic fungus Candida albicans. The presence of a functional endogenous pathway of NAD biosynthesis from tryptophan was demonstrated. In addition, nicotinamide served as an efficient salvage precursor for NAD biosynthesis but nicotinate was not utilized. The pathway for nicotinamide utilization involved nicotinate and nicotinate nucleotides as intermediates, suggesting that the failure to utilize nicotinate involves a transport defect. The mechanisms that regulate NAD levels during exponential growth operated to maintain constant NAD levels when NAD biosynthesis occurred exclusively from endogenous or salvage pathways or from a combination of the two. The regulation also operated such that the salvage pathway was preferentially utilized.

Biological Transport↗
PubMed1977

Chromatographic separation of pyridine and adenine nucleotides on thin layers of poly(ethyleneimine) cellulose.

The chromatographic properties on thin layers of poly(ethyleneimine) cellulose of sixteen compounds containing the pyridine and/or adenine ring have been studied. Chromatographic mobilities have been examined as a function of the concentration of lithium chloride or sodium formate buffer in the chromatographic solvent. These data provide a rationale for the development of rapid and simple separation methods that should prove useful in the study of pyridine and adenine nucleotide metabolism.

Adenine Nucleotides↗