Dynamics of social and energetic stress in wild female chimpanzees

Stress hormone measurements can reinforce and refine hypotheses about the costs of particular contexts or behaviors in wild animals. For social species, this is complicated because potential stressors may come from the physical environment, social environment, or some combination of both, while the stress response itself is generalized. Here, we present a multivariate examination of urinary cortisol dynamics over 6 years in the lives of wild female chimpanzees in the Kanyawara community of Kibale National Park, Uganda. We hypothesized that chimpanzee socioecology provides strong indications of both energetic and social stress to females, but that the salience of these stressors might vary over a female's life history in accordance with their changing reproductive costs and social interactions. Using linear mixed models, we found that urinary cortisol levels increased significantly with age but were also elevated in young immigrants to the community. Across reproductive states, cycling, non-estrous females had relatively low cortisol compared to lactating, estrous, or pregnant females. Aggression from males led to higher cortisol levels among estrous females, frequent targets of aggressive sexual coercion. In contrast, energetic stress was most salient to lactating females, who experienced higher cortisol during months of low fruit consumption. Low dominance rank was associated with increased cortisol, particularly during the energetically demanding period of lactation. The effects of female conflict were felt widely, even among those who were the primary aggressors, providing further evidence that long-term resource competition, while apparently muted, exerts a far-reaching impact on the lives of chimpanzee females.     

Fecal glucocorticoids as indicators of metabolic stress in female Sykes' monkeys (Cercopithecus mitis albogularis)

Because of their mediating role in the stress response and potential effects on fitness, glucocorticoid (GC) hormones are increasingly used to assess the physiological costs of environmental and behavioral variation among wild vertebrates. Identifying the proximate causes of GC variation, however, is complicated by simultaneous exposure to multiple potentially stressful stimuli. Here, we use data from a partially provisioned social group of Sykes' monkeys to evaluate the effects of potential psychological and metabolic stressors on temporal and individual variation in fecal GC (fGC) excretion among 11 adult females. Despite high rates of agonism over provisioned foods fGCs declined during periods of high provisioning frequency when fruit availability was dominated by neem (Azadirachta indica), an item requiring great feeding effort. Provisioned foods did not prevent fGC increases when availability of the most preferred main fruit item, tamarind (Tamarindus indica), declined drastically. Although rank-related differences in access to provisioned foods and rates of agonism did not lead to an overall effect of rank on fGCs, low-ranking females excreted more fGCs than high-ranking females during a period of high provisioning intensity and low fruit availability. The emergence of this rank effect was associated with elevated feeding effort in all females, a greater access to provisioned items by high-ranking females, and a higher proportion of time spent moving in low-ranking females. Our findings suggest that metabolic stressors were the primary determinants of both temporal and individual variation in fGCs, indicating potential fitness benefits for high-ranking females when food availability is limited.     

The cross-generation transmission of oxytocin in humans

Animal studies demonstrated that the neuropeptide oxytocin (OT), implicated in bond formation across mammalian species, is transmitted from mother to young through mechanisms of early social experiences; however, no research has addressed the cross-generation transmission of OT in humans. Fifty-five parents (36 mothers and 19 fathers) engaged in a 15-min interaction with their infants. Baseline plasma OT was sampled from parents and salivary OT was sampled from parents and infants before and after play and analyzed with ELISA methods. Interactions were micro-coded for parent and child's socio-affective behavior. Parent and infant's salivary OT was individually stable across assessments and showed an increase from pre- to post-interaction. Significant correlations emerged between parental and infant OT at both assessments and higher OT levels in parent and child were related to greater affect synchrony and infant social engagement. Parent-infant affect synchrony moderated the relations between parental and infant OT and the associations between OT in parent and child were stronger under conditions of high affect synchrony. Results demonstrate consistency in the neuroendocrine system supporting bond formation in humans and other mammals and underscore the role of early experience in shaping the cross-generation transmission of social affiliation in humans.     

Paired-Pulse Facilitation of Transmitter Release at Different Levels of Extracellular Calcium Concentration

High-frequency synaptic activity can cause facilitation of transmitter release due to accumulation of “residual Ca²⁺” at the nerve terminal. However, the mechanism of this phenomenon is still under debate. Here we show that, using extracellular recording from frog cutaneous pectoris muscle, paired-pulse facilitation (PPF) at the frog neuro-muscular junction decays in two or three-exponential manner depending upon the extracellular Ca²⁺ concentration ([Ca²⁺]_e). First, second and “early” PPF components are analyzed and described in this study. Considering the dependence of PPF on [Ca²⁺]_e, existence of several specific high-affinity intra-terminal Ca²⁺-binding sites that underlie the facilitation of transmitter release at the frog neuro-muscular junction is proposed.     

Philopatry, nest choice, and aggregation temporal–spatial change in the digger wasp Cerceris arenaria (Hymenoptera: Crabronidae)

Studying temporal and spatial changes of aggregations of digger wasps through nesting seasons is interesting because of its link to social evolution via a semi-social pathway, but information about this topic is scarce. An aggregation of Cerceris arenaria Latreille was studied during 1997–1999 and for a short period in 2001. The colony grew in area and number of nests through the first three seasons, but the aggregation reduced in 2001, and this decrease was confirmed by a count of nests made in 2003 and 2005. The positions of the nest entrances remained almost constant over the years, at least in high-nest-density areas, because of the repeated use of the same burrows from which they emerged. This fact permits the population to exploit for many years a restricted area and could act as a nest-density-regulation method for fossorial species that rarely dig new nests, preventing an excessive nest density. The newly emerged females did not dig new nests, showed a high philopatry in the choice of their first nest, and preferred to look for other nests to occupy close to the ones recently abandoned (mainly for an undergone usurpation by a conspecific female). Philopatry, along with lack of new nest digging and position-dependent nest choice, is probably an important factor maintaining spatial stability of the aggregation through the years and could represent a first step in the evolution of a higher sociality in apoid burrowing Hymenoptera.     

Vocal communication in adult greater horseshoe bats, Rhinolophus ferrumequinum

Whereas echolocation in horseshoe bats is well studied, virtually nothing is known about characteristics and function of their communication calls. Therefore, the communication calls produced by a group of captive adult greater horseshoe bats were recorded during various social interactions in a free-flight facility. Analysis revealed that this species exhibited an amazingly rich repertoire of vocalizations varying in numerous spectro-temporal aspects. Calls were classified into 17 syllable types (ten simple syllables and seven composites). Syllables were combined into six types of simple phrases and four combination phrases. The majority of syllables had durations of more than 100 ms with multiple harmonics and fundamental frequencies usually above 20 kHz, although some of them were also audible to humans. Preliminary behavioral observations indicated that many calls were emitted during direct interaction with and in response to social calls from conspecifics without requiring physical contact. Some echolocation-like vocalizations also appeared to clearly serve a communication role. These results not only shed light upon a so far widely neglected aspect of horseshoe bat vocalizations, but also provide the basis for future studies on the neural control of the production of communicative vocalizations in contrast to the production of echolocation pulse sequences.     

Pioneer dwarf willow may facilitate tree succession by providing late colonizers with compatible ectomycorrhizal fungi in a primary successional volcanic desert

To advance understanding of the contribution of ectomycorrhizal (ECM) fungi to tree successional processes, natural establishment patterns of secondary colonizing hosts and their ECM fungal communities were investigated with special reference to pioneer hosts. In the volcanic desert on Mount Fuji, Japan, vegetation is sparsely distributed, resembling islands in a sea of scoria. Of 509 vegetation islands in the research area, 161 contained Salix reinii (Salix), the first colonizing ECM host species. The spatial coincidence between secondary colonizing timber species and Salix was analysed, and ECM fungal communities were studied using molecular identification methods. I found 39 and 26 individuals of Betula ermanii and Larix kaempferi, respectively. Without exception, these individuals were all accompanied by Salix. The ECM fungal communities of these timber species showed high similarity to that of Salix and were dominated by generalists that were compatible with two or more plant families. In this desert, available ECM propagules are limited. Pioneer Salix may contribute to tree succession by providing adjacent late colonizers with compatible ECM fungal symbionts.     

Root distribution and interactions between intercropped species

Even though ecologists and agronomists have considered the spatial root distribution of plants to be important for interspecific interactions in natural and agricultural ecosystems, few experimental studies have quantified patterns of root distribution dynamics and their impacts on interspecific interactions. A field experiment was conducted to investigate the relationship between root distribution and interspecific interactions between intercropped plants. Roots were sampled twice by auger and twice by the monolith method in wheat (Triticum aestivum L.)/maize (Zea mays L.) and faba bean (Vicia faba L.)/maize intercropping and in sole wheat, maize, and faba bean up to 100 cm depth in the soil profile. The results showed that the roots of intercropped wheat spread under maize plants, and had much greater root length density (RLD) at all soil depths than sole wheat. The roots of maize intercropped with wheat were limited laterally, but had a greater RLD than sole-cropped maize. The RLD of maize intercropped with faba bean at different soil depths was influenced by intercropping to a smaller extent compared to maize intercropped with wheat. Faba bean had a relatively shallow root distribution, and the roots of intercropped maize spread underneath them. The results support the hypotheses that the overyielding of species showing benefit in the asymmetric interspecific facilitation results from greater lateral deployment of roots and increased RLD, and that compatibility of the spatial root distribution of intercropped species contributes to symmetric interspecific facilitation in the faba bean/maize intercropping. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Sex-specific life history patterns in bluegill (Lepomis macrochirus): interacting mechanisms influence individual body size

The ultimate body size that an individual fish achieves can be a function both of direct effects of growth or indirect effects associated with the timing of sexual maturation (and associated energetic tradeoffs). These alternatives are often invoked to explain variation in body size within and among fish populations, but have rarely been considered simultaneously. We assessed how resource availability and timing of maturation interact to influence individual body size of bluegill (Lepomis macrochirus). Resource availability (high and low food) and the social structure of the population (presence or absence of large, mature males) were varied in experimental ponds. Food ration affected growth (larger fish in the high food treatments) and the social structure of the population affected timing of maturation (early maturation of males in the absence of large males). Treatment effects, however, were sex-specific; males responded to the social structure of the population and females were more responsive to resource availability. We also found individuals that became sexually mature were smaller than those that remained immature, although results were sex-specific and resource dependent. For males, individuals that matured were smaller when resources were limited; mature and immature females showed no difference in body size regardless of food ration. We show that both resource availability and the processes that control timing of maturation interact in sex-specific ways to influence body size of bluegill. These results suggest that a more robust explanation for variable body size requires consideration of sex-specific interactions between ecological (food and growth) and evolutionary (timing of maturation) mechanisms.