Repeatable glucocorticoid expression is associated with behavioural syndromes in males but not females in a wild primate.

Behavioural syndromes are a well-established phenomenon in human and non-human animal behavioural ecology. However, the mechanisms that lead to correlations among behaviours and individual consistency in their expression at the apparent expense of behavioural plasticity remain unclear. The 'state-dependent' hypothesis posits that inter-individual variation in behaviour arises from inter-individual variation in state and that the relative stability of these states within an individual leads to consistency of behaviour. The endocrine stress response, in part mediated by glucocorticoids (GCs), is a proposed behavioural syndrome-associated state as GC levels are linked to an individual's behavioural responses to stressors. In this study, in wild Barbary macaques (Macaca sylvanus), consistent inter-individual differences were observed in both sexes for GC activity (faecal glucocorticoid, fGC concentrations), but not GC variation (coefficient of variation in fGC concentrations). The expression of the behavioural syndrome 'Excitability' (characterized by the frequencies of brief affiliation or aggressive interactions) was related to GC activity in males but not in females; more 'excitable' males had lower GC activity. There was no relationship in females between any of the behavioural syndromes and GC activity, nor in either sex with GC variation. The negative relationship between GC activity and Excitability in males provides some support for GC expression as a behavioural syndrome-generating state under the state-dependent framework. The absence of this relationship in females highlights that state-behavioural syndrome associations may not be generalizable within a species and that broader sex differences in state need to be considered for understanding the emergence and maintenance of behavioural syndromes.

Assessing adaptability and reactive scope: Introducing a new measure and illustrating its use through a case study of environmental stress in forest-living baboons.

In order to maintain regulatory processes, animals are expected to be adapted to the range of environmental stressors usually encountered in their environmental niche. The available capacity of their stress responses is termed their reactive scope, which is utilised to a greater or lesser extent to deal with different stressors. Typically, non-invasive hormone assessment is used to measure the physiological stress responses of wild animals, but, for methodological reasons, such measurements are not directly comparable across studies, limiting interpretation. To overcome this constraint, we propose a new measure of the relative strength of stress responses, 'demonstrated reactive scope', and illustrate its use in a study of ecological correlates (climate, food availability) of faecal glucocorticoid (fGC) levels in two forest-living troops of baboons. Results suggest the wild-feeding troop experiences both thermoregulatory and nutritional stress, while the crop-raiding troop experiences only thermoregulatory stress. This difference, together with the crop-raiding troop's lower overall physiological stress levels and lower demonstrated fGC reactive scope, may reflect nutritional stress-buffering in this troop. The relatively high demonstrated fGC reactive scope levels of both troops compared with other baboons and primate species, may reflect their extreme habitat, on the edge of the geographic range for baboons. Demonstrated reactive scope provides a means of gauging the relative strengths of stress responses of individuals, populations, or species under different conditions, enhancing the interpretive capacity of non-invasive studies of stress hormone levels in wild populations, e.g. in terms of animals' adaptive flexibility, the magnitude of their response to anthropogenic change, or the severity of impact of environmental conditions.

Influence of diet and stress on reproductive hormones in Nigerian olive baboons.

A female mammal's reproductive function and output are limited by the energy she is able to extract from her environment. Previous studies of the interrelationships between energetic circumstances and reproductive function in a variety of mammal species have produced varied results, which do not all support the common assumption that higher female reproductive hormone levels, specifically progesterone, indicate better ovarian function and greater reproductive potential, and are associated with lower energetic stress. In the present study faecal progesterone and glucocorticoid levels were assessed in two troops of olive baboons (Papio anubis) in the same population. They face similar ecological challenges, except that one troop crop-raids, potentially affecting its energetic intake and stress levels. The energy intake of individual females was assessed by combining detailed feeding observations with nutritional analysis of food samples. The crop-raiding troop experienced 50% higher energy intake rates and 50% lower glucocorticoid levels compared to the non-crop-raiding troop alongside substantially lower progesterone levels. This suggests that energetic stress is associated with elevated progesterone levels and may be the cause of the non-crop-raiding troop's lower reproductive output. By comparing groups which differ little, except in terms of food access, and also by directly assessing energy intake, our study addresses some of the design limitations of previous research investigating variation in progesterone levels and energetic stress. It therefore has the potential to contribute to greater understanding of the factors affecting differences in reproductive and stress hormone levels and reproductive function in mammals experiencing different energetic circumstances.

Social capital and physiological stress levels in free-ranging adult female rhesus macaques.

Social animals with greater access to social support, i.e. higher levels of social capital, may be able to cope better with the challenges they face in their day-to-day lives, and this may be reflected in lower physiological stress levels. Here, we examine the relationship between social capital and fecal glucocorticoid (GC) levels in pregnant free-ranging adult female rhesus macaques. In addition to social capital measures based on direct connections between social partners, which have been examined previously, we use social network analysis to generate measures of social capital based on indirect connections (i.e. connections between pairs of individuals which result from their mutual direct connection to a third party). We consider social capital based on three different types of affiliative association: grooming, the exchange of affiliative vocalizations and proximity. After controlling for variables known to affect GC output in primates (e.g. month of pregnancy), GC levels of females were significantly predicted by a social network measure of indirect connectedness in the proximity network, proximity reach, in interaction with dominance rank. High ranking females had significantly lower GC levels in months in which they had low levels of proximity reach (i.e. in months in which their proximity networks were smaller and therefore more focused). The results of our study add to a growing body of evidence which suggests that social capital may be an important means by which gregarious animals cope with day-to-day challenges. Our study also joins a small body of recent research which has demonstrated that indirect connections may be important factors in the lives of social animals.

Comment on "The Brain of LB1, Homo floresiensis".

Endocast analysis of the brain Homo floresiensis by Falk et al. (Reports, 8 April 2005, p. 242) implies that the hominid is an insular dwarf derived from H. erectus, but its tiny cranial capacity cannot result from normal dwarfing. Consideration of more appropriate microcephalic syndromes and specimens supports the hypothesis of modern human microcephaly.

The evolution of non-maternal care in anthropoid primates: a test of the hypotheses.

The amount of non-maternal care (allocare) found in primates varies greatly from species to species. Our paper examines this variation and focuses on possible reasons why mothers in some anthropoid primate species are prepared to relinquish their infants to other carers whereas others are not. We use data collected from the literature to test a number of hypotheses that attempt to explain the observed variation in non-maternal care. Analyses were carried out using comparative methods that control for the influence of both body size and phylogeny on life-history and ecological variation. The results support previous studies of both primates and other mammals in finding a clear link between the amount of allocare provided and female reproductive rates. Species with high allocare levels grow rapidly post-natally and wean their infants at a younger age (but at the same relative size) than species of the same body size with lower allocare levels. This early weaning allows high allocare species to support higher birth rates than low allocare species but does not result in earlier maturation. Our results, therefore, suggest that mothers allow non-maternal care of their infants in order to increase their own reproductive output. It is not clear whether such a strategy also benefits the infant, as we could find no link between the presence of allocare and early maturation (which would increase the infant's reproductive output) or between allocare levels and infant survival (as measured by vulnerability to infanticide). This suggests that mothers and infants might come into conflict over transfer to other carers, as the benefits to the mother may not be accompanied by benefits to the infant. However, although mothers may benefit from allocare in some circumstances, they will not be expected to allow allocare if the costs are high (e.g. if there is a high risk to the infant).

The evolution of human speech: the role of enhanced breathing control.

Many cognitive and physical features must have undergone change for the evolution of fully modern human language. One neglected aspect is the evolution of increased breathing control. Evidence presented herein shows that modern humans and Neanderthals have an expanded thoracic vertebral canal compared with australopithecines and Homo ergaster, who had canals of the same relative size as extant nonhuman primates. Based on previously published analyses, these results demonstrate that there was an increase in thoracic innervation during human evolution. Possible explanations for this increase include postural control for bipedalism, increased difficulty of parturition, respiration for endurance running, an aquatic phase, and choking avoidance. These can all be ruled out, either because of their evolutionary timing, or because they are insufficiently demanding neurologically. The remaining possible functional cause is increased control of breathing for speech. The main muscles involved in the fine control of human speech breathing are the intercostals and a set of abdominal muscles which are all thoracically innervated. Modifications to quiet breathing are essential for modern human speech, enabling the production of long phrases on single expirations punctuated with quick inspirations at meaningful linguistic breaks. Other linguistically important features affected by variation in subglottal air pressure include emphasis of particular sound units, and control of pitch and intonation. Subtle, complex muscle movements, integrated with cognitive factors, are involved. The vocalizations of nonhuman primates involve markedly less respiratory control. Without sophisticated breath control, early hominids would only have been capable of short, unmodulated utterances, like those of extant nonhuman primates. Fine respiratory control, a necessary component for fully modern language, evolved sometime between 1.6 Mya and 100,000 ya.

Applications of the reflex instruments in quantitative morphology.

The Reflex instruments are a set of non-contact measuring instruments enabling direct measurement in three dimensions of relatively small objects, or of stereophotographs. In addition to the range of geometric calculations which the standard software provided with the instruments can perform directly on the output of three-dimensional coordinates, the data can also be used to generate contour plots, three-dimensional computer representations, etc. The instruments have been used to measure hard tissues such a s teeth, jaws and vertebrae, soft tissues such as gums, leg ulcers an Drosophila, and impressions such a s footprints and bitemarks. Among the advantages of the instruments, in different studies their use has improved precision, speeded up measurement, avoided the need to take X-rays and avoided possible damage to objects.