Leakey Foundation Final Report Social, ecological and reproductive stress in wild female Assamese macaques Julia Ostner, Courant Research Center Evolution of Social Behavior, University of Göttingen; Germany, jostner@gwdg.de
Summary Physiological stress may - if chronic - become detrimental to an individual’s fitness partly due to the immunosuppressive and dysregulatory effects of GC. Although a large body of research on stress exists, there remain large gaps in our understanding, as most studies focus on just one type of stressor. Thus, we set out to investigate potential ecological, social and reproductive sources of stress and their relative impact on the endocrine stress response, measured via fecal glucocorticoid metabolites. To do so we collected data on social behavior, food abundance and intake along with hormonal data on physiological stress on all adult females of a group of wild Assamese macaques at Phu Khieo Wildlife Sanctuary. In a first step we investigated social effects on the physiological stress response and found significant seasonal differences in same and opposite sex social interaction patterns which in turn predicted fecal glucocorticoid output (Fürtbauer et al. 2014). Specifically, in the non-mating season when females mainly associated with females and only infrequently with males, female-female affiliation predicted lower stress levels, whereas during the mating season male-female interaction rates and patterns predicted fecal glucocorticoid levels (Fürtbauer et al. 2014). These results indicate i) that opposite just as well as same sex social interactions can attenuate the stress response and ii) that their relative importance may fluctuate with seasonal or life stage specific needs. In a next step we will combine nutritional, behavioral and reproductive data to investigate their relative influence on stress physiology in wild macaque females (I. Fürtbauer, O. Schülke, M. Heistermann, J. Ostner, unpubl, data). Publication plans The first set of results covering the effects of same and opposite sex sociality on the physiological stress response has recently been published (Fürtbauer et al. 2014). The further aim of this project, i.e. disentangling nutritional reproductive and psychosocial sources of stress will be prepared for submission in the next months. The final step will be to combine data on the sources of stress, physiological stress levels and health outcome into one comprehensive picture. Project Overview This study aimed to investigate and unravel potential ecological, psychosocial, and reproductive sources of stress and their relative impact on the endocrine stress response, i.e. fecal glucocorticoid (fGC) output, in wild female Assamese macaques (Macaca assamensis) living at Phu Khieo Wildlife Sanctuary, Northeastern Thailand. It specifically centered around three main objectives: first, we aimed to disentangle the ecological, social and reproductive sources of physiological stress employing a multivariate approach and data on individual energy intake, reproductive status and social factors. Second, we aimed to investigate how social factor would influence an individual’s stress response and coping mechanisms. Finally, we aimed to investigate the physiological costs and possible benefits females experience when being consorted by males. The project capitalized on a dataset consisting of more than 2000 hours of focal observations and 2558 fecal samples for 1
measurement of glucocorticoid metabolites collected of 16 adult females from one social group between Sept 2007 and February 2009. In addition, data on monthly food availability as well as nutritional content of ~70 important food items were available. The funds provided by the Leakey Foundation allowed us to carry out hormone analyses. Analyses were led by Dr Ines Fürtbauer postdoctoral fellow in collaboration with Dr Michael Heistermann, head of the Endocrinology Laboratory at the German Primate Center. Methods Study site and study group The study was carried out at Phu Khieo Wildlife Sanctuary (PKWS), northeastern Thailand at 16°0535’N and 101°20-55’E. The sanctuary covers an area of 1573 km2 at elevations of 300 - 1300 m above sea level, and is part of the approximately 6500 km2 Western Isaan Forest Complex (Koenig et al. 2004). For details on the study site see Borries et al. (2002) and Schülke et al. (2011). Data for this project were collected between September 2007 and February 2009 on 15 individual adult females of one fully habituated group of wild Assamese macaques. Across the study period group size varied with 12-14 adult females, 13-15 adult males and a number of immature individuals. The sampling period included two mating seasons from October to early February and one non-mating season (late February – September)(Fürtbauer et al. 2010; Fürtbauer et al. 2011). This study was conducted completely non-invasively and under the permission of the Department of National Parks, Wildlife and Plant Conservation (DNP) and the National Research Council of Thailand (NRCT) (permit 0004.3/3618). Behavioral data collection We conducted focal animal recordings on adult females (Altmann 1974). Focal protocols (20-30min length) included an instantaneous and a continuous part. During instantaneous sampling (10 min sampling interval) the proximity between the focal female and all other group members within a 5m radius was recorded. During continuous sampling all affiliative, agonistic and sexual behavior was recorded. During the mating seasons sexual consortships which can last up to several weeks (Fürtbauer et al. 2011; Ostner et al. 2011; Schülke et al. 2014) were also recorded. Over 2,000 hours of focal data were collected. Additionally, ad libitum data on submissive behavior were recorded to construct a dominance hierarchy using clearly submissive signals (Ostner et al. 2008). Female dominance rank was assessed using the I&SI method as implemented in MATMAN 1.1.4 (Noldus 2003). Hormonal data Approximately 2500 fecal samples were collected directly after defecation from individually recognized females. Samples were homogenized in the field and 5-15g wet weight was collected, stored cold during the day and immediately transferred into a freezer upon return to the field camp. Frozen samples were transported to the Endocrinology lab of the German Primate Center where they were measured for immunoreactive glucocorticoid metabolites using an assay previously applied to several primate species (Heistermann et al. 2006) including Assamese macaques (Ostner et al. 2008; Schülke et al. 2014). For details on hormone analyses see Fürtbauer et al. (2014). Ecological data As part of the long term project we assess food abundance once a month by monitoring up to 650 trees, shrubs and climbers spread over the group’s home range including 57 important food items 2
making up for approximately 70% of monthly feeding time on plant matter (for details see Heesen et al. 2013). Based on these assessments we calculate an index of fruit availability for each calendar month. Food availability in the study group has been shown to be positively related to female energy intake and conception rates (Heesen et al. 2013). Results Same and opposite-sex effects on physiological stress Our first publication based on the results generated in this project summarizes the effects of same, i.e. female-female, and opposite-sex, i.e. female-male, sociality on female physiological stress levels (Fürtbauer et al. 2014). It is well-known that female-female social affiliation and strong social relationships can provide fitness benefits, such as increased infant survival and longevity (Silk et al. 2003; Silk et al. 2009). If females are lacking these relationships, and thus social needs are unfulfilled, allostatic load (McEwen and Wingfield 2003; Creel et al. 2013) will be increased. Increased glucocorticoid levels after the loss of a close affiliate or in females lacking close relationships in times of stress exemplifies this relationship (Engh et al. 2006; Wittig et al. 2008). Similarly, male-female friendly (non-sexual) interactions may be beneficial to a female (Nguyen et al. 2009; Palombit 2009) and may thus also be reflected in a female’s glucocorticoid levels, as has been seen in female baboons, where females with a male “friend” showed lower GC levels during a socially stressful time compared to females without such a male affiliate (Beehner et al. 2005). Thus, affiliative social interactions with both – male and female – partners positively influence the stress response. Previous studies did not consider both factors simultaneously in the same species and at the same time and concentrated on aseasonal species and thus likely stable social needs. Our project focusses on Assamese macaques, a highly seasonal species, with pronounced male-female interactions during the brief annual mating season, and year-round female-female interactions consistent with the cercopithecine matrilineal society. We predicted that female glucocorticoid levels would be predicted by female-female affiliation in the mating and non-mating season, whereas male-female sociality should only determine female stress levels during the mating season. For details on the following results please see Fürtbauer et al. (2014). Analyses of the behavioral data clearly confirmed a seasonal change in male-female sociality, with male-female grooming rates and time in proximity being significantly increased during the mating compared to the non-mating season. Female-female grooming rates in contrast remained the same across the two seasons, while time spent in proximity was significantly higher during the non-mating season (Wilcoxon tests, N = 7 females: female - male grooming: p < 0.05, T = 0.00; female - male proximity: p < 0.05, T = 0.00; female – female grooming: p = 0.87, T = -15.00; female – female proximity: p < 0.05, T = 0.00). Glucocorticoid metabolite excretion was influenced by female reproductive state with pregnant and lactating females showing significantly higher GC levels compared to acyclic or cyclic females. Female dominance rank did not predict GC excretion. In a GLMM we found that in our sample of 15 females female glucocorticoid levels during the mating season were significantly predicted by female – male sociality (GLMM: estimate ± se = -0.07 ± 0.02, p = 0.0012), a principle component consisting of female-male grooming rates, number of male grooming partners and female-male proximity (principle components identified in a Principal Component Analysis). Thus, females grooming less with males or spending less time in proximity with males during the mating season exhibited higher glucocorticoid levels. Contrary to our prediction, female-female sociality (a component including female - female grooming rates, number of female 3
grooming partners and female - female proximity) did not predict female glucocorticoids during this season (GLMM: estimate ± se = -0.003 ± 0.03, p = 0.3774). As predicted, during the non-mating season female-female sociality predicted lower glucocorticoid levels (GLMM: estimate ± se = -0.11 ± 0.03, p = 0.0036), whereas male- female sociality did not (GLMM: estimate ± se = 0.02 ± 0.03, p = 0.7386), indicating that females that groomed more often or with more female grooming partners or spent more time in proximity with females experienced lower physiological stress. In summary our results are in line with other data indicating that affiliative social interactions affects allostatic load. As such physiological stress may be one of the key mediators linking sociality and fitness. In order to better understand this mechanistic level, we will in further analyses investigate the effect of social bonding as opposed to general sociality and social support on the physiological stress response. Our data contributes to the body of research on sociality-stress-health by providing evidence for differential effects of male and female sociality depending on differing social needs during different life stages, i.e. mating vs non-mating. Disentangling sources of stress As a next step we will investigate the simultaneous effects of reproductive status (acyclic, cyclic, pregnant, lactating), food availability and intake, and social factors (dominance rank, aggression, social bonds) on individual females physiological stress level. Measurement of fecal glucocorticoid metabolites across the females of the study group revealed a pronounced month-to-month variation (Fig. 1). These data need to be investigated on an individual level to contribute to a more comprehensive picture of the various sources of physiological stress and their effects on female primates. These findings will extend beyond Assamese macaques to other female primates, especially those living in seasonal habitats and in socially complex societies.
We will also integrate results from this study with research on the sociality – health link as it has been shown that in humans and nonhuman animals social stress influences the onset and progression of diseases and generally reduces life expectancy (Capitanio et al. 1998; HoltLunstad et al. 2010; Miller 2011). Gastro-intestinal parasite samples are collected as part of our routine long-term project. We thus aim to the data of various sources (social, physiological stress and health) to gain a better understanding of how these factors ultimately modulate an individual’s fitness.
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mean GC [μg/g dry mass] Figure 1: Monthly means (and standard errors) of glucocorticoid metabolite level of 15 individual female Assamese macaques across the study period. Red bars denote the mating season, blue bars rainy and black bars dry season. References Altmann J (1974) Observational study of behavior: sampling methods. Behaviour 49:227-267 Beehner J, Bergman T, Cheney D, Seyfarth R, Whitten P (2005) The effect of new alpha males on female stress in free-ranging baboons. Animal Behaviour 69:1211-1221 Borries C, Larney E, Kreetiyutanont K, Koenig A (2002) The diurnal primate community in a dry evergreen forest in Phu Khieo Wildlife Sanctuary, Northeast Thailand. Natural History Bulletin of the Siam Society 50:75-88 Capitanio JP, Mendoza SP, Lerche NW, Mason WA (1998) Social stress results in altered glucocorticoid regulation and shorter survival in simian acquired immune deficiency syndrome. Proceedings of the National Academy of Sciences 95:4714-4719 Creel S, Dantzer B, Goymann W, Rubenstein DR (2013) The ecology of stress: effects of the social environment. Functional Ecology 27:66-80 Engh A, Beehner J, Bergman C, Whitten P, Hoffmeier R, Seyfarth RM, Cheney DL (2006) Behavioural and hormonal responses to predation in female chacma baboons (Papio hamadryas ursinus). Proceedings of the Royal Society London B 273:707-712 Fürtbauer I, Heistermann M, Schülke O, Ostner J (2011) Concealed fertility and extended female sexuality in a non-human primate (Macaca assamensis). PLoS ONE 6:e23105 Fürtbauer I, Heistermann M, Schülke O, Ostner J (2014) Low female stress hormone levels are predicted by same- or opposite-sex socialitydepending on season in wild Assamese macaques. Psychoneuroendocrinology 48:19-28
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