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Admixture between diverging taxa has made, and continues to make, an important contribution to primate diversity and evolution. However, although naturally occurring hybrids have now been documented in all major primate lineages, we still know relatively little about the factors that shape when and where admixture occurs. Baboons (genus Papio), in which multiple natural hybrid zones are well described, provide a valuable system to investigate these factors. Here, we combined Geographic Information Systems and weather station data with information on genetically characterized populations in southern Kenya to investigate if ecological variables present a potential barrier to gene flow between anubis baboons and yellow baboons in the region. Specifically, we asked if altitude, seasonal temperature, or seasonal precipitation differ for weather stations in anubis, yellow, or hybrid ranges in southern Kenya, and if land cover or altitude covary with population ancestry near the hybrid zone. Our analyses suggest that the range of yellow baboons in Kenya is climatically distinct from the range of anubis baboons, with hybrids in intermediate regions. However, we identified no clear pattern of climate or land cover differentiation near the hybrid zone itself. Thus, when yellow baboons and anubis baboons come into contact, our data suggest that the resulting population composition is not consistently predicted by the ecological variables we considered. Our results support the designation of baboons as highly flexible "generalists," and suggest that more fine-grained analyses (e.g., relative success in ecologically stressful years) may be necessary to detect clear signals of ecological barriers to gene flow. [ABSTRACT FROM AUTHOR]

How female mammals adapt metabolically in response to environmental variation remains understudied in the wild, because direct measures of metabolic activity are difficult to obtain in wild populations. However, recent advances in the non-invasive measurement of fecal thyroid hormones, triiodothyronine (T3), an important regulator of metabolism, provide an opportunity to understand how female baboons living in the harsh Amboseli ecosystem in southern Kenya adapt to environmental variability and escape strict reproductive seasonality. Specifically, we assessed how a female's activity budget, diet, and concentrations of fecal T3 metabolites (mT3) changed over the course of the year and between years. We then tested which of several environmental variables (season, rainfall, and temperature) and behavioral variables (female activity budget and diet) best predicted mT3 concentrations. Finally, we determined if two important reproductive events – onset of ovarian cycling and conception of an offspring – were preceded by changes in female mT3 concentrations. We found female baboons' mT3 concentrations varied markedly across the year and between years as a function of environmental conditions. Further, changes in a female's behavior and diet only partially mediated the metabolic response to the environment. Finally, mT3 concentrations increased in the weeks prior to menarche and cycling resumption, regardless of the month or season in which cycling started. This pattern indicates that metabolic activation may be an indicator of reproductive readiness in female baboons as their energy balance is restored. • Metabolic response to environment is understudied in wild animal populations. • Fecal thyroid hormone concentrations can be used to estimate metabolic activity. • Female baboons showed evidence of seasonal and yearly variation in their metabolism. • Changes in their behavior and diet only partially mediate metabolic response to environment. • Metabolic activation precedes onset of female baboon sexual cycling. [ABSTRACT FROM AUTHOR]

Relatives have more similar gut microbiomes than nonrelatives, but the degree to which this similarity results from shared genotypes versus shared environments has been controversial. Here, we leveraged 16,234 gut microbiome profiles, collected over 14 years from 585 wild baboons, to reveal that host genetic effects on the gut microbiome are nearly universal. Controlling for diet, age, and socioecological variation, 97% of microbiome phenotypes were significantly heritable, including several reported as heritable in humans. Heritability was typically low (mean = 0.068) but was systematically greater in the dry season, with low diet diversity, and in older hosts. We show that longitudinal profiles and large sample sizes are crucial to quantifying microbiome heritability, and indicate scope for selection on microbiome characteristics as a host phenotype. [ABSTRACT FROM AUTHOR]

Abstract: Environmental stressors impact physiology and behavior in many species of animals. These effects are partly mediated through changing concentrations of glucocorticoids, which also vary with reproductive state and social conditions. Prior research has focused largely on seasonal breeders, but the close temporal linkage between season and reproductive state in these species hinders ability to disentangle environmental effects from those of the animal''s reproductive status. Here we assessed the effects of environmental challenges on the fecal glucocorticoid (fGC) levels of non-seasonal breeders, female baboons (Papio cynocephalus) of Amboseli, Kenya. Amboseli is characterized by a long dry season, during which food and water become scarce, and by extreme temperatures above 40 °C in the shade during some months of the year. We found that after accounting for female reproductive status and individual variability, females exhibited higher fGC levels during the dry season than during the wet season. Further, during the wet season, fGC levels were higher in months of high average daily maximum temperatures. During the dry season, fGC levels were elevated both in hotter months and in months during which the baboons spent a relatively high proportion of time feeding. In spite of these stressors, female baboons reproduce during all months of the year in Amboseli, unlike most other mammals in this environment. This may be attributable to their extreme adaptability, specifically their diversified diet, and their ability to modify their behavior, including their activity profiles. [Copyright &y& Elsevier]

In vertebrates, glucocorticoid secretion occurs in response to energetic and psychosocial stressors that trigger the hypothalamic-pituitary-adrenal (HPA) axis. Measuring glucocorticoid concentrations can therefore shed light on the stressors associated with different social and environmental variables, including dominance rank. Using 14,172 fecal samples from 237 wild female baboons, we test the hypothesis that high-ranking females experience fewer psychosocial and/or energetic stressors than lower-ranking females. We predicted that high-ranking females would have lower fecal glucocorticoid (fGC) concentrations than low-ranking females. Because dominance rank can be measured in multiple ways, we employ an information theoretic approach to compare 5 different measures of rank as predictors of fGC concentrations: ordinal rank; proportional rank; Elo rating; and two approaches to categorical ranking (alpha vs non-alpha and high-middle-low). Our hypothesis was supported, but it was also too simplistic. We found that alpha females exhibited substantially lower fGCs than other females (typical reduction = 8.2%). If we used proportional rank instead of alpha versus non-alpha status in the model, we observed a weak effect of rank such that fGCs rose 4.2% from the highest- to lowest-ranking female in the hierarchy. Models using ordinal rank, Elo rating, or high-middle-low categories alone failed to explain variation in female fGCs. Our findings shed new light on the association between dominance rank and the stress response, the competitive landscape of female baboons as compared to males, and the assumptions inherent in a researcher's choice of rank metric. Unlabelled Image • Alpha status predicts low fecal glucocorticoid concentrations in female baboons. • Proportional (i.e., 'relative' or 'standardized') rank was also a weak predictor. • Other rank metrics were poor predictors of fecal glucocorticoid concentrations. • Our results shed light on within-group competitive processes. [ABSTRACT FROM AUTHOR]