Biomedical subjects
Publications and source records attributed to Robert A Barton.
A new study of contact calls in dolphins shows that individuals can recognize one another using information encoded in the frequency modulation pattern of these calls, in the absence of general voice characteristics.
Primates are usually thought of as "visual" mammals, and several comparative studies have emphasized the role of vision in primate neural and sociocognitive specialization. Here I explore the role of olfactory systems, using phylogenetic analysis of comparative volumetric data. The relative sizes of the main olfactory bulb (MOB) and accessory olfactory bulb (AOB) tend to show different evolutionary patterns in accordance with their different functions. Although there is some evidence of correlated evolution of the two systems, this is apparent in only one clade (the strepsirhines). As predicted, the MOBs correlate predominantly with ecological factors (activity period and diet), while the AOBs correlate with social and mating systems. Related olfactory structures (i.e., the piriform cortex and amygdala) exhibit correlated evolution with the AOBs but not with the MOBs, and the corticobasolateral part of the amygdala exhibits a correlation with social group size in platyrrhines similar to that observed for the AOB. These social system correlations support the idea that there is an olfactory dimension to the concept of the social brain.
The amygdala and hypothalamus become sexually differentiated by gonadal hormones giving rise to sexually differentiated behaviors, which include play behavior. Phylogenetic comparative analyses test for relationships between social play and brain structure volumes. Relative volume of the amygdala and hypothalamus correlated with social play, but not nonsocial play, even after controlling for the size of other brain structures. The authors propose that behaviors such as social assessment, recognizing and responding to facial expression, and social response appropriateness, which are mediated by the amygdala, are developed through social play. Additionally, the hypothalamus may regulate the motivation to engage in play through positive reinforcement of pleasurable activity. Thus, the instinctive socio-emotive aspects of play in primates appear to be those regulated by the amygdala and hypothalamus.
Red coloration is a sexually selected, testosterone-dependent signal of male quality in a variety of animals, and in some non-human species a male's dominance can be experimentally increased by attaching artificial red stimuli. Here we show that a similar effect can influence the outcome of physical contests in humans--across a range of sports, we find that wearing red is consistently associated with a higher probability of winning. These results indicate not only that sexual selection may have influenced the evolution of human response to colours, but also that the colour of sportswear needs to be taken into account to ensure a level playing field in sport.
Coevolutionary interactions such as those between hosts and parasites have been regarded as an underlying cause of evolutionary diversification, but evidence from natural populations is limited. Among primates and other mammalian groups, measures of host diversification rates vary widely among lineages, but comparative studies have not yet identified a reliable explanation for this variation. In this study, we used a comprehensive data set of disease-causing organisms from free-living primates to illustrate how phylogenetic comparative methods can be used to examine mammalian lineage diversity in relation to parasite species richness. Our results provide evidence that the phylogenetic diversity of primate clades is correlated positively with the number of parasite species harbored by each host and that this pattern is largely independent of other host traits that have been shown to influence diversification rates and parasite species richness in primates. We investigated two possible mechanisms that could explain this association, namely that parasites themselves drive host evolutionary diversification through processes linked with sexual selection and that host shifts or host sharing increases parasite species richness among diverse primate clades. Neither parasite species richness nor host diversification is related to measures of sexual selection in primates. Further, we found only partial evidence that more rapidly diversifying host lineages produced increased opportunities for host sharing or host shifting by parasites through mechanisms involving species' geographic range overlap. Thus, our analyses provide evidence for an important link between the evolutionary diversification of primates and the richness of their parasite communities, but other mechanisms, particularly those related to reciprocal selection or coextinction of hosts and parasites, require further investigation.
Despite great interest in the role of the amygdala in animal and human behaviour, its very existence as a structurally and functionally unified brain component has been questioned, on the grounds that cell groups within it display divergent pharmacological and connectional characteristics. We argue that the question of whether particular brain nuclei constitute a valid structural and functional unit is inherently an evolutionary question, and we present a method for answering it. The method involves phylogenetic analysis of comparative data to determine whether or not separate regions of the putative brain structure show statistically correlated evolution. We find that, in three separate groups of mammals (primates and two groups of insectivores), evolutionary changes in the volumes of amygdala components are strongly correlated, even after controlling for volumetric change in a wide range of limbic and other brain structures. This allows us to reject the strong claim that the amygdala is neither a structural nor a functional unit, and demonstrates the importance of evolutionary analysis in resolving such issues in systems neuroscience.
Three reports on mammalian brain evolution analyse the same comparative data on brain component volumes but come to partially conflicting conclusions. Clark et al. conclude from their analysis of volumetric brain proportions ("cerebro-types") that cerebellum size is invariant across mammalian taxonomic groups, the neocortex and cerebellum do not co-vary in size (in contradiction to ref. 1), and cerebrotype-based measures identify directional changes in brain architecture. Here I provide evidence that calls each of these conclusions into question. The failure of the cerebrotype measure to identify species differences in brain architecture that are independent of gross brain size undermines the proposal by Clark et al. that it could be useful for detecting evolutionary patterns and phylogenetic relationships.