Functional host-specific adaptation of the intestinal microbiome in hominids.

Fine-scale knowledge of the changes in composition and function of the human gut microbiome compared that of our closest relatives is critical for understanding the evolutionary processes underlying its developmental trajectory. To infer taxonomic and functional changes in the gut microbiome across hominids at different timescales, we perform high-resolution metagenomic-based analyzes of the fecal microbiome from over two hundred samples including diverse human populations, as well as wild-living chimpanzees, bonobos, and gorillas. We find human-associated taxa depleted within non-human apes and patterns of host-specific gut microbiota, suggesting the widespread acquisition of novel microbial clades along the evolutionary divergence of hosts. In contrast, we reveal multiple lines of evidence for a pervasive loss of diversity in human populations in correlation with a high Human Development Index, including evolutionarily conserved clades. Similarly, patterns of co-phylogeny between microbes and hosts are found to be disrupted in humans. Together with identifying individual microbial taxa and functional adaptations that correlate to host phylogeny, these findings offer insights into specific candidates playing a role in the diverging trajectories of the gut microbiome of hominids. We find that repeated horizontal gene transfer and gene loss, as well as the adaptation to transient microaerobic conditions appear to have played a role in the evolution of the human gut microbiome.

Stratigraphy of stable isotope ratios and leaf structure within an African rainforest canopy with implications for primate isotope ecology.

The canopy effect describes vertical variation in the isotope ratios of carbon (δ13C), oxygen (δ18O) and partially nitrogen (δ15N) within plants throughout a closed canopy forest, and may facilitate the study of canopy feeding niches in arboreal primates. However, the nuanced relationship between leaf height, sunlight exposure and the resulting variation in isotope ratios and leaf mass per area (LMA) has not been documented for an African rainforest. Here, we present δ13C, δ18O and δ15N values of leaves (n = 321) systematically collected from 58 primate food plants throughout the canopy (0.3 to 42 m) in Côte d'Ivoire, West Africa. Besides leaf sample height and light availability, we measured leaf nitrogen and carbon content (%N, %C), as well as LMA (n = 214) to address the plants' vertical resource allocations. We found significant variation in δ13C, δ18O and δ15N, as well as LMA in response to height in combination with light availability and tree species, with low canopy leaves depleted in 13C, 18O and 15N and slightly higher in %N compared to higher canopy strata. While this vertical isotopic variation was not well reflected in the δ13C and δ15N of arboreal primates from this forest, it did correspond well to primate δ18O values.

Cortisol and oxytocin show independent activity during chimpanzee intergroup conflict.

The oxytocinergic system is involved in a range of functions, from attachment and social bonding to aggression and stress responses. Whether oxytocin is released in response to a stressor, shows contradictory results across species and potential contexts-dependent differences. To avoid unintended contextual changes due to experimental procedures, we tested this question non-invasively in wild chimpanzees in an ecologically valid context. We collected endogenous hormonal measures during exposure to a known natural stressor, intergroup conflict. Specifically, we tested for potential synchronous activation patterns between urinary oxytocin and cortisol in male and female chimpanzees during stressor exposure. Oxytocinergic system reactivity during chimpanzee intergroup conflict has already been established in this study population. Thus, we first investigated urinary cortisol levels during border patrol and intergroup encounter days, in comparison to another potential stressor, hunting, and control days. We found higher urinary cortisol levels during intergroup encounter days compared with control and hunting days. We then compared secretion patterns of oxytocin and cortisol in relation to increased levels of out-group contact and hostility ('out-group risk') during intergroup conflict. We found that increased 'out-group risk' was associated with higher cortisol levels, especially when involving direct visual or physical contact with rival groups. Although urinary oxytocin levels were high across intergroup conflict contexts, increasing levels of out-group risk showed no significant variation. Taken together, results indicate independent secretion of oxytocin and cortisol during chimpanzee intergroup conflict, emphasizing that stressor exposure in this context is not the main trigger of oxytocin secretion.

Social bonds facilitate cooperative resource sharing in wild chimpanzees.

Why share when access to benefits is uncertain is crucial to our understanding of the evolution of humans' extensive cooperation. Here, we investigated some of the different human sharing hypotheses and potential neuroendocrine mechanisms, in one of our closest living relatives, chimpanzees. The strongest predictor of sharing across food types was the presence of enduring and mutually preferred grooming partners, more than harassment, direct signalling, or trade. Moreover, urinary oxytocin levels were higher after the sharing of both individually and jointly acquired resources compared with controls. We conclude that the emotional connection inherent in social bonds was a key factor determining sharing patterns, with the oxytocinergic system potentially facilitating long-term cooperative exchanges. Testing for the role of social bonds in increasing predictability of sharing behaviour, a feature frequently overlooked, may help us to identify the evolutionary drivers of resource sharing and mechanisms that sustain delayed reciprocity between non-kin.

Urinary oxytocin levels in relation to post-conflict affiliations in wild male chimpanzees (Pan troglodytes verus).

Many animals living in social groups have evolved behaviors to resolve conflicts between group members, behaviors thought crucial for maintaining stable group life. Several hypotheses, based mainly on observational data, aim to explain how post-conflict (PC) affiliations, such as reconciliation and consolation, resolve conflicts by restoring relationships and/or alleviating anxiety. To examine a potential endocrinological mechanism of PC affiliations, we used an experimental-like procedure to investigate whether the oxytocinergic system is activated during naturally observed reconciliations, receiving bystander PC affiliations and aggressions not followed by PC affiliations in wild male chimpanzees. We compared urinary oxytocin (uOT) levels after reconciliations, receiving bystander PC affiliations or aggressions without affiliations with two control conditions: affiliations without previous aggression and after time periods without social interactions. We furthermore tested the 'valuable relationship' hypothesis of reconciliation, as well as the influence of relationship quality between individuals engaged in each of the three behavioral conditions involving aggression on uOT levels. We found that the probability to reconcile a conflict increased with increasing relationship quality between opponents, thus our results support the 'valuable relationship' hypothesis. However, relationship quality did not influence uOT levels, while behavioral condition had a significant effect on uOT levels. uOT levels after reconciliations, receiving bystander PC affiliations and affiliations not related to conflicts were higher than after aggressions alone and time periods without social interactions. Overall, our results indicate that the oxytocinergic system is activated during affiliative interactions, whether occurring as reconciliation, bystander PC affiliation or affiliation alone. We conclude that the oxytocinergic system, in addition to building and maintaining social relationships, also takes part in repairing them.

Tools for opening new chapters in the book of Treponema pallidum evolutionary history.

Treponema pallidum infections causing yaws disease and venereal syphilis are globally widespread in human populations, infecting hundreds of thousands and millions annually respectively; endemic syphilis is much less common, and pinta has not been observed in decades. We discuss controversy surrounding the origin, evolution and history of these pathogens in light of available molecular and anthropological evidence. These bacteria (or close relatives) seem to affect many wild African nonhuman primate (NHP) species, though to date only a single NHP Treponema pallidum genome has been published, hindering detection of spillover events and our understanding of potential wildlife reservoirs. Similarly, only ten genomes of Treponema pallidum infecting humans have been published, impeding a full understanding of their diversity and evolutionary history. Research efforts have been hampered by the difficulty of culturing and propagating Treponema pallidum. Here we highlight avenues of research recently opened by the coupling of hybridization capture and next-generation sequencing. We present data generated with such an approach suggesting that asymptomatic bones from NHP occasionally contain enough treponemal DNA to recover large fractions of their genomes. We expect that these methods, which naturally can be applied to modern biopsy samples and ancient human bones, will soon considerably improve our understanding of these enigmatic pathogens and lay rest to old yet unresolved controversies.

Urinary oxytocin and social bonding in related and unrelated wild chimpanzees.

Animals that maintain cooperative relationships show gains in longevity and offspring survival. However, little is known about the cognitive or hormonal mechanisms involved in cooperation. Indeed, there is little support for a main hypothesis that non-human animals have the cognitive capacities required for bookkeeping of cooperative exchanges. We tested an alternative hypothesis that cooperative relationships are facilitated by an endocrinological mechanism involving oxytocin, a hormone required for bonding in parental and sexual relationships across mammals. We measured urinary oxytocin after single bouts of grooming in wild chimpanzees. Oxytocin levels were higher after grooming with bond partners compared with non-bond partners or after no grooming, regardless of genetic relatedness or sexual interest. We ruled out other possible confounds, such as grooming duration, grooming direction or sampling regime issues, indicating that changes in oxytocin levels were mediated by social bond strength. Oxytocin, which is thought to act directly on neural reward and social memory systems, is likely to play a key role in keeping track of social interactions with multiple individuals over time. The evolutionary linkage of an ancestral hormonal system with complex social cognition may be the primary mechanism through which long-term cooperative relationships develop between both kin and non-kin in mammals.

Simultaneous observations of haemolymph flow and ventilation in marine spider crabs at different temperatures: a flow weighted MRI study.

In vivo magnetic resonance imaging (MRI) and angiography were applied to the marine spider crab Maja squinado for a study of temperature effects and thermal tolerance. Ventilation and haemolymph circulation were investigated during progressive cooling from 12 degrees C to 2 degrees C. The anatomical resolution of MR images from Maja squinado obtained with a standard spin echo sequence were suitable to resolve the structures of various internal organs. The heart of the animal could be depicted without movement artifacts. The use of a flow compensated gradient echo sequence allowed simultaneous observations of ventilation, reflected by water flow through the gill chambers as well as of haemolymph flow. Simultaneous investigation of various arteries was possible by use of flow weighted MRI. In addition to those accessible by standard invasive flow sensitive doppler sensors, flow changes in gill, leg arteries and the venous return could be observed. Both ventilation and haemolymph flow decreased during progressive cooling and changes in haemolymph flow varied between arteries. Haemolymph flow through the Arteria sternalis, some gill and leg arteries was maintained at low temperatures indicating a reduced thermal sensitivity of flow in selected vessels. In support of previous invasive studies of haemolymph flow as well as heart and ventilation rates, the results demonstrate that the operation of gills and the maintenance of locomotor activity are critical for cold tolerance. A shift in haemolymph flow between arteries likely occurs to ensure the functioning of locomotion and ventilation in the cold.

Metabolic state of Zymomonas mobilis in glucose-, fructose-, and xylose-fed continuous cultures as analysed by 13C- and 31P-NMR spectroscopy.

The reasons for the well-known significantly different behaviour of the anaerobic, gram-negative, ethanologenic bacterium Zymomonas mobilis during growth on fructose (i.e. decreased growth and ethanol yields, increased by-product formation) as compared to that on its second natural substrate, glucose, have remained unexplained. A xylose-fermenting recombinant strain of Z. mobilis that was recently constructed in our laboratory also unexpectedly displayed an increased formation of by-products and a strongly reduced growth rate as compared to the parent strain. Therefore, a comprehensive study employing recently developed NMR-based methods for the in vivo analysis of intracellular phosphorylated pool sizes and metabolic fluxes was undertaken to enable a global characterization of the intracellular metabolic state of Z. mobilis during growth on 13C-labelled glucose, fructose and xylose in defined continuous cultures. The 13C-NMR flux analysis indicated that ribose 5-phosphate is synthesized via the nonoxidative pentose phosphate pathway in Z. mobilis, and it identified a metabolic bottleneck in the recombinant xylose-fermenting Z. mobilis strain at the level of heterologous xylulokinase. The 31P-NMR analyses revealed a global alteration of the levels of intracellular phosphorylated metabolites during growth on fructose as compared to that on glucose. The results suggest that this is primarily caused by an elevated concentration of intracellular fructose 6-phosphate.

Ethanol transport in Zymomonas mobilis measured by using in vivo nuclear magnetic resonance spin transfer.

For the first time, unidirectional rate constants of ethanol diffusion through the lipid membrane of a microorganism, the bacterium Zymomonas mobilis, were determined, thus replacing indirect inferences with direct kinetic data. The rate constants k1 (in to out) were 6.8 +/- 0.4s(-1) at 29 degrees C and 2.7 +/- 0.3s(-1) at 20 degrees C. They were determined by using 1H selective nuclear magnetic resonance spin magnetization transfer. The measurements were done on l-ml cell suspensions. No addition of radiotracers, withdrawing of aliquots, physical separation methods, or chemical manipulations were required. Until now, the rate constants of ethanol transport in microorganisms have been unknown because ethanol diffuses through the cytoplasmic membrane too quickly for radiolabel approaches. Net velocities of ethanol exchange were calculated from unidirectional rate constants and cytoplasmic volume, which was also determined with the same nuclear magnetic resonance experiments. The results (i) confirmed that ethanol would not be rate limiting during the conversion of glucose by Z. mobilis and (ii) indicated that ethanol can serve as an in vivo marker of cytoplasmic volume changes. This was verified by monitoring for the first time the changes of both cytoplasmic volume and extracytoplasmic and cytoplasmic concentrations of alpha and beta anomers of D-glucose in cell suspensions of a microorganism. These findings may open up new possibilities for kinetic studies of ethanol and sugar transport in Z. mobilis and other organisms.

HLA DR2 in narcolepsy with sleep-onset REM periods but not cataplexy.

To determine the association of HLA DR2 in patients with narcolepsy without cataplexy, a case-control study was performed. Patients receiving the diagnosis of narcolepsy without cataplexy had excessive daytime sleepiness (EDS) and polysomnographic findings consistent with narcolepsy but no clinical evidence of cataplexy. Of 28 patients identified, 12 agreed to return for HLA typing. Respondents did not differ from nonrespondents in demographic, clinical, or sleep laboratory data. The comparison group was 503 individuals, those 30 years and older, on the Michigan Kidney Transplant Registry. The odds ratio obtained from logistic regression indicated a strong association between narcolepsy without cataplexy and HLA DR2. To control for potential confounding variables, multivariate models were constructed to explore the joint effects of HLA DR2 and each one of the covariates (age, sex, and race), their possible combinations, and the effect of all three covariates. The odds ratios decreased minimally and the association between the disease and HLA DR2 remained significant.

Subjective and polysomnographic characteristics of patients diagnosed with narcolepsy.

In order to better characterize the subjective and polysomnographic findings in patients with narcolepsy, a follow-up questionnaire was mailed to all patients diagnosed with the disorder at the Henry Ford Hospital Sleep Disorders and Research Center. The questionnaire inquired regarding the present, previous, and change in status for the constellation of narcolepsy symptoms. Memory problems, problems of daytime function, and nocturnal sleep disturbance were included among the questions related to the symptomatic constellation. By definition, all patients were symptomatic of daytime sleepiness and were diagnosed with narcolepsy only if there were two or more rapid eye movement (REM) onsets documented on the polysomnographic evaluation. A high percentage of patients reported nocturnal sleep disturbance, which was one of the symptoms with the latest reported onset. Retrospective comparison of questionnaire responses to the clinical polysomnography revealed significantly more sleep maintenance difficulties in the group of patients reporting this symptom on the questionnaire. Patients with disturbed nocturnal sleep reported taking more naps during the day, although the Multiple Sleep Latency Test (MSLT) failed to show differences in sleep latency. Interestingly, this group of patients was found to have a significantly higher number of sleep onset REM episodes on the MSLT. Finally, the findings are discussed as they compare to studies that required the presence of cataplexy as part of their inclusion criteria.

Fragmented sleep, daytime somnolence and age in narcolepsy.

This study examined whether narcoleptics experience an age-related increase in nocturnal sleep disturbance and, if so, what impact that disturbance has on daytime sleepiness. To evaluate these questions, the records of 228 patients diagnosed as narcoleptic were assessed. Total sleep time (TST) and sleep efficiency (SE) significantly decreased, and wake during sleep (WDS), number of awakenings, and percentage of stage one significantly increased across the decades. This indicates an age-related elevation in sleep fragmentation. Daytime sleepiness, however, did not exhibit age effects. These data further support the theory that narcolepsy is a basic neural defect not confounded by excessive daytime sleepiness secondary to sleep fragmentation.

Dose determinants of rebound insomnia.

A polysomnographic assessment in healthy normal sleepers of possible dose relations for rebound insomnia was conducted. As an additional measure of rebound the study included a direct test of sleep/wake tendency during the night of drug discontinuation. Twelve, healthy men (21-30 years) each received placebo, 0.25 mg and 0.50 mg triazolam for 6 consecutive nights followed by a discontinuation night and 14 nights of recovery at home. The three conditions were presented, double-blind, in a latin square design. On night 6 of drug administration both doses increased total sleep time compared to placebo, but 0.50 mg did not improve sleep beyond 0.25 mg. On drug discontinuation (night 7) wake time over the 8 h recording and sleep latency after an experimental awakening (02.30 h) were increased with 0.50 mg compared to placebo and 0.25 mg. On these measures of rebound 0.25 mg did not differ from placebo. Thus rebound insomnia occurred only at a dose (0.50 mg) which produced no additional hypnotic efficacy in these normal sleepers. Whether tests of sleep/wake tendency make a useful measure of rebound insomnia needs further clarification.