Direct fitness of group living mammals varies with breeding strategy, climate and fitness estimates

Systematic review assessing the effects of amendments on acidic soils pH in tea plantations

Soil acidification has emerged as a critical limiting factor for the sustainable development of the tea industry. In this article, a comprehensive review of 63 original research articles focusing on the impact of amendments on the pH in tea plantations soil was conducted. Through meta-analysis, the effect of applying soil amendments to increase the pH of tea plantation soil and its influencing factors were investigated. The results revealed that lime had a significant impact, increasing the pH by 18% in tea plantation soil, while rapeseed cake had a minimal (2%) effect. It was observed that as the quantity of amendments and pH levels increased, so did their impact on the pH of tea plantation soil. Subgroup analysis within biochar showed varying effects, depending on soil pH, with an 11% increase in acidic soil. Among these amendments, biochar produced at pyrolysis temperature ranging from 501-600 °C and derived from animal waste demonstrated significant effect on increasing soil pH in tea plantations by 9% and 12%, respectively. This study offers valuable insights into improving and ensuring the health and sustainability of tea plantations.

Impact of prolonged chronic social isolation stress on behavior and multifractal complexity of metabolic rate in Octodon degus

Social interaction can improve animal performance through the prevention of stress-related events, the provision of security, and the enhancement of reproductive output and survival. We investigated the effects of prolonged chronic social isolation stress on behavioral, cognitive, and physiological performance in the social, long-lived rodent Octodon degus. Degu pups were separated into two social stress treatments: control (CTRL) and chronically isolated (CI) individuals from post-natal and post-weaning until adulthood. We quantified anxiety-like behavior and cognitive performance with a battery of behavioral tests. Additionally, we measured their basal metabolic rate (BMR) and analyzed the multifractal properties of the oxygen consumption time series using Multifractal Detrended Fluctuation Analysis, a well-known method for assessing the fractal characteristics of biological signals. Our results showed that CI induced a significant increase in anxiety-like behaviors and led to a reduction in social and working memory in male degus. In addition, CI-treated degus reduced the multifractal complexity of BMR compared to CTRL, which implies a decrease in the ability to respond to environmental stressors and, as a result, an unhealthy state. In contrast, we did not observe significant effects of social stress on BMR. Multivariate analyses showed a clear separation of behavior and physiological variables into two clusters, corresponding to CI and CTRL degus. This study provides novel insights into the effects of prolonged chronic social isolation stress on behavior, cognitive performance, and metabolic complexity in this rodent animal model. To the best of our knowledge, it is the first study to integrate cognitive-behavioral performance and multifractal dynamics of a physiological signal in response to prolonged social isolation. These findings highlight the importance of social interactions for the well-being and overall performance of social animals.

Damaraland mole-rats do not rely on helpers for reproduction or survival

In eusocial invertebrates and obligate cooperative breeders, successful reproduction is dependent on assistance from non-breeding group members. Although naked (Heterocephalus glaber) and Damaraland mole-rats (Fukomys damarensis) are often described as eusocial and their groups are suggested to resemble those of eusocial insects more closely than groups of any other vertebrate, the extent to which breeding individuals benefit from the assistance of non-breeding group members is unclear. Here we show that, in wild Damaraland mole-rats, prospective female breeders usually disperse and settle alone in new burrow systems where they show high survival rates and remain in good body condition-often for several years-before being joined by males. In contrast to many obligate cooperative vertebrates, pairs reproduced successfully without non-breeding helpers, and the breeding success of experimentally formed pairs was similar to that of larger, established groups. Though larger breeding groups recruited slightly more pups than smaller groups, adult survival was independent of group size and group size had mixed effects on the growth of non-breeders. Our results suggest that Damaraland mole-rats do not need groups to survive and that cooperative breeding in the species is not obligate as pairs can-and frequently do-reproduce without the assistance of helpers. While re-emphasizing the importance of ecological constraints on dispersal in social mole-rats, the mixed effects of group size in our study suggest that indirect benefits accrued through cooperative behavior may have played a less prominent role in the evolution of mole-rat group-living than previously thought.

The evolution of marsupial social organization

It is generally believed that marsupials are more primitive than placentals mammals and mainly solitary living, representing the ancestral form of social organization of all mammals. However, field studies have observed pair and group-living in marsupial species, but no comparative study about their social evolution was ever done. Here, we describe the results of primary literature research on marsupial social organization which indicates that most species can live in pairs or groups and many show intra-specific variation in social organization. Using Bayesian phylogenetic mixed-effects models with a weak phylogenetic signal of 0.18, we found that solitary living was the most likely ancestral form (35% posterior probability), but had high uncertainty, and the combined probability of a partly sociable marsupial ancestor (65%) should not be overlooked. For Australian marsupials, group-living species were less likely to be found in tropical rainforest, and species with a variable social organization were associated with low and unpredictable precipitation representing deserts. Our results suggest that modern marsupials are more sociable than previously believed and that there is no strong support that their ancestral state was strictly solitary living, such that the assumption of a solitary ancestral state of all mammals may also need reconsideration.

Maternal survival costs in an asocial mammal

Maternal characteristics, social dynamics, and environmental factors can all influence reproduction and survival and shape trade‐offs that might arise between these components of fitness. Short‐lived mammals like the golden‐mantled ground squirrel (GMGS; Callospermophilus lateralis) tend to maximize effort toward current reproduction at the expense of survival but may be complicated by other aspects of the species’ life history and environment. Here, we use 25 years of data (1995–2020) collected from a population of GMGS at the Rocky Mountain Biological Research Laboratory in Gothic, Colorado, to test the effect of several maternal characteristics (e.g., age, experience, and timing of litter emergence), social context (e.g., litter sex ratio and kin density), and environmental context (e.g., date of bare ground and length of vegetative growing season) on survival of reproductive female GMGS using Cox proportional hazard models. Our results indicated that social dynamics (i.e., density) and environmental conditions (i.e., standardized first day of permanent snow cover and length of growing season) explained significant variation in annual maternal survival, while maternal characteristics did not. A higher density of related breeding females and the total number of females (both related and unrelated to the focal mother) were associated with an increase in the mortality hazard. A later standardized date of the first day of permanent snow cover and a shorter growing season both reduced the maternal mortality hazard. Together, our results suggest that factors extrinsic to the squirrels affect maternal survival and thus may also influence local population growth and dynamics in GMGS and other short‐lived, territorial mammal species.

We used 25 years of longitudinal data collected from golden‐mantled ground squirrel females to test the effects of individual characteristics, the social context, and the environment on female mortality using Cox proportional hazard models. Both female kin density and the environmental context explained significant variation in female mortality, while individual characteristics did not. Our results suggest that both kin density and climate metrics related to growing season phenology swamp individual characteristics in explaining variability in maternal mortality. This is an important finding in a rather short‐lived species where every additional active season survived has a lot of weight in improving lifetime reproduction.

Exploring the Relationship Between Social Ties and Resilience From Evolutionary Framework

This conceptual paper examines the necessity and importance of social bonds and networks in building resilience to fight the COVID-19. Resilience is a quality that energizes an individual’s actions and acts as a buffer to stressful events. The current article is intended to explore the evolutionary programmed behavior of the human mind to make social ties and structure. Humans have a strong need to connect and relate with other individuals by developing cooperation and perspective-taking. The ability to make social connections, group living, and sharing resources had a selective advantage in coping with physical and psychological stress. Social bonds provide resilience to people’s approach while making adjustments and adapting to situations, thus presents fitness benefits at both group and individual levels. An attempt has also been made to address how social isolation as a strategy to contain the infection adversely influence body homeostasis. Finally, this article recommends health practitioners, clinicians, and researchers to encourage research on the impact of social isolation/social interaction on mental and physical health indicators.

Multi-year assessment of variability in spatial and social relationships in a subterranean rodent, the highland tuco-tuco (Ctenomys opimus)

Abstract

In some species, populations routinely contain a mixture of lone and group-living individuals. Such facultative sociality may reflect individual differences in behavior as well as adaptive responses to variation in local environmental conditions. To explore interactions between individual- and population-level variabilities in behavior in a species provisionally described as facultatively social, we examined spatial and social relationships within a population of highland tuco-tucos (Ctenomys opimus) at Laguna de los Pozuelos, Jujuy Province, Argentina. Using data collected over 5 consecutive years, we sought to (1) confirm the regular occurrence of both lone and group-living individuals and (2) characterize the temporal consistency of individual social relationships. Our analyses revealed that although the study population typically contained lone as well as group-living animals, individual spatial and social relationships varied markedly over time. Specifically, the extent to which individuals remained resident in the same location across years varied, as did the number of conspecifics with which an animal lived, with an overall tendency for individuals to live in larger groups over successive years. Collectively, these analyses indicate that population-level patterns of behavior in C. opimus are consistent with facultative sociality but that this variation does not arise due to persistent differences in individual behavior (i.e., living alone versus with conspecifics). Instead, based on changes in spatial and social relationships across years, we suggest that variation in the tendency to live in groups is shaped primarily by local ecological and demographic conditions.

Significance statement

Characterizing variation in conspecific relationships is critical to understanding the adaptive bases for social behavior. Using data collected over 5 successive years, we examined temporal variation in spatial and social relationships within a population of highland tuco-tucos (C. opimus) from northern Argentina. In addition to providing the first multi-year assessment of the behavior and demography of this species, our analyses generate important insights into relationships between individual behavior and population-level patterns of social organization. The behavioral variability evident in our study population suggests that C. opimus is an ideal system in which to explore the causes and consequences of individual differences in social behavior.

"Live together, die alone": The effect of re-socialization on behavioural performance and social-affective brain-related proteins after a long-term chronic social isolation stress

Loneliness affects group-living mammals triggering a cascade of stress-dependent physiological disorders. Indeed, social isolation stress is a major risk factor for several neuropsychiatric disorders including anxiety and depression. Furthermore, social isolation has a negative impact on health and fitness. However, the neurobiological consequences of long-term chronic social isolation stress (LTCSIS) manifested during the adulthood of affected individuals are not fully understood. Our study assessed the impact of LTCSIS and social buffering (re-socialization) on the behavioural performance and social-affective brain-related proteins in diurnal, social, and long-lived Octodon degus (degus). Thereby, anxiety-like and social behaviour, and social recognition memory were assessed in male and female animals subjected to a variety of stress-inducing treatments applied from post-natal and post-weaning until their adulthood. Additionally, we evaluated the relationship among LTCSIS, Oxytocin levels (OXT), and OXT-Ca2+-signalling proteins in the hypothalamus, the hippocampus, and the prefrontal cortex. Our findings suggest that LTCSIS induces anxiety like-behaviour and impairs social novelty preference whereas sociability is unaffected. On the other hand, re-socialization can revert both isolation-induced anxiety and social memory impairment. However, OXT and its signalling remained reduced in the abovementioned brain areas, suggesting that the observed changes in OXT-Ca2+ pathway proteins were permanent in male and female degus. Based on these findings, we conclude degus experience social stress differently, suggesting the existence of sex-related mechanisms to cope with specific adaptive challenges.

Influence of biochar and soil properties on soil and plant tissue concentrations of Cd and Pb: A meta-analysis

The application of biochar to soils contaminated with potentially toxic elements (PTEs) has received particular attention due to its ability to reduce PTE uptake by the plants. Therefore, we conducted a meta-analysis to identify Cd and Pb concentrations in plant shoots and roots in response to biochar application and soil properties. We collected data from 65 peer-reviewed journal articles published from 2009 to 2020 in which 66% of manuscripts were published from 2015 to 2020. The data were processed using OpenMEE software. The results pinpointed that addition of biochar to soil caused a significant decrease in shoot and root Cd and Pb concentrations as compared to untreated soils with biochar (control), and the reduction rate was affected by plant types and both biochar and soil properties. The biochar size less than 2 mm, biochar pH higher than 10, pyrolysis temperature of 401-600 °C, and the application rate higher than 2% appeared to be effective in reducing shoot and root Cd and Pb concentration. Soil properties such as pH, SOC, and texture influenced the efficiency of biochar for reducing plant Cd and Pb uptake. Biochar application increased SOC (54.3%), CEC (48.0%), pH (0.08), and EC (59.4%), and reduced soil extractable Cd (42.1%) and Pb (47.1%) concentration in comparison to control. A detailed study on the rhizosphere chemistry and uptake mechanism will help to underpin the biochar application rates and their efficiency reducing PTE mobility and plant uptake.

Higher sociability leads to lower reproductive success in female kangaroos

In social mammals, social integration is generally assumed to improve females' reproductive success. Most species demonstrating this relationship exhibit complex forms of social bonds and interactions. However, female eastern grey kangaroos (Macropus giganteus) exhibit differentiated social relationships, yet do not appear to cooperate directly. It is unclear what the fitness consequences of such sociability could be in species that do not exhibit obvious forms of cooperation. Using 4 years of life history, spatial and social data from a wild population of approximately 200 individually recognizable female eastern grey kangaroos, we tested whether higher levels of sociability are associated with greater reproductive success. Contrary to expectations, we found that the size of a female's social network, her numbers of preferential associations with other females and her group sizes all negatively influenced her reproductive success. These factors influenced the survival of dependent young that had left the pouch rather than those that were still in the pouch. We also show that primiparous females (first-time breeders) were less likely to have surviving young. Our findings suggest that social bonds are not always beneficial for reproductive success in group-living species, and that female kangaroos may experience trade-offs between successfully rearing young and maintaining affiliative relationships.

Non-invasive estimation of the costs of feeding competition in a neotropical primate

A key goal in behavioral ecology is to investigate the factors influencing the access to food resources and energetic condition of females, which are strong predictors of their reproductive success. We aimed to investigate how ecological factors, social factors, and reproductive state are associated with energetic condition in a wild neotropical primate using non-invasive measures. We first assessed and compared urinary C-peptide levels (uCP), the presence of urinary ketones (uKet), and behaviorally assessed energy balance (bEB) in female white-faced capuchin monkeys (Cebus imitator) living in Santa Rosa, Costa Rica. Then, we assessed how these measures were associated with feeding competition, dominance rank, and reproductive state. As predicted, uCP and bEB were positively associated with each other, and bEB was negatively associated with uKet. However, we did not find a relationship between uCP and uKet. Females showed lower uCP and bEB values during periods of intense feeding competition, but this relationship was not dependent on dominance rank. Furthermore, rank was not directly associated with uCP and bEB. Urinary ketones, on the other hand, were only produced in the most adverse conditions: by low-ranking, lactating females during periods of intense feeding competition. Behavioral strategies are assumed to maximize reproductive success and not energetic condition per se, which might explain why rank was not generally associated with energetic condition in our study population. This highlights the importance of considering potential differences between reproductive success and proxies of reproductive success, such as energetic condition or food intake, when investigating predictions of socioecological models.

Integrating Fitness Components Reveals That Survival Costs Outweigh Other Benefits and Costs of Group Living in Two Closely Related Species

Group living can be beneficial when individuals reproduce or survive better in the presence of others, but, simultaneously, there might be costs due to competition for resources. Positive and negative effects on various fitness components might thus counteract each other, so integration is essential to determine their overall effect. Here, we investigated how an integrated fitness measure (reproductive values [RVs]) based on six fitness components varied with group size among group members in cooperatively breeding red-winged and superb fairy wrens (Malurus elegans and Malurus cyaneus, respectively). Despite life-history differences between the species, patterns of RVs were similar, suggesting that the same behavioral mechanisms are important. Group living reduced RVs for dominant males, but for other group members, this was true only in large groups. Decomposition analyses showed that our integrated fitness proxy was most strongly affected by group size effects on survival and was amplified through carryover effects between years. Our study shows that integrative consideration of fitness components and subsequent decomposition analysis provide much needed insights into the key behavioral mechanisms shaping the costs and benefits of group living. Such attribution is crucial if we are to synthesize the relative importance of the myriad group size costs and benefits currently reported in the literature.

The first assessment of social organisation of the Indian Ocean humpback dolphin (Sousa plumbea) along the south coast of South Africa

The Indian Ocean humpback dolphin (Sousa plumbea (G. Cuvier, 1829)) is the most endangered marine mammal species in South Africa, and the overall decline of its abundance and group size may affect the social organisation of the species, potentially accentuating its vulnerability. Understanding the social organisation is therefore particularly relevant to conservation efforts. From photo-identification surveys along the south coast of South Africa from March 2014 to June 2015, we quantified association patterns and investigated the social organisation of Indian Ocean humpback dolphins using the half-weight index, social cluster, and network analyses. During the 101 surveys conducted and 553 h of survey effort, 98 sightings of dolphins were recorded and 65 individuals identified. Using individuals seen at least three times, this study reveals that the social network is well differentiated, as strong social divisions exist between individuals that seem to be split into four distinctive social clusters. Network strength was low; approximately half of the associations were low to moderate, whereas some individuals were strongly associated, especially between four pairs of individuals. Although this study is based on a limited number of individuals, our study nevertheless suggests that the atypical strong social bonds recorded here could result from behavioural responses following the decline in group size and abundance.

Weighing density and kinship: Aggressive behavior and time allocation in fire salamander (Salamandra infraimmaculata)

Kin-biased behavior (that is responding differentially to kin and non-kin) is thought to be adaptive in many social interactions. One example of this kin bias is behaving less aggressively toward a relative than a non-relative, a behavior which yields inclusive fitness benefits. However, data are lacking about the ability of animals to weigh their preference for kinship and the density of conspecifics simultaneously and to respond accordingly. Fire salamanders (Salamandra infraimmaculata) larviposit in high densities in ponds. Thus, larvae of different females confront competition and predation by other larvae. We studied whether larvae prefer their kin over particular density or vice versa. We experimentally used a transparent glass aquarium with inner chambers to test the responses of a focal larva toward its siblings and non-siblings. Specifically, we quantified the time a focal larva spent near its siblings or non-siblings, presented in varying densities, and the aggression level it demonstrated. We found that focal larvae spent more time near non-siblings if non-sibling and sibling groups were of equal density. The focal larvae were also more aggressive toward non-siblings. The results may be explained by the cannibalistic nature of these larvae: high density may provide more opportunities for food, especially when non-siblings are present. Further explanations for these findings may include other advantages of staying in a larger group and/or the stronger olfactory and visual stimulation offered by groups compared to a single individual. These findings suggest that larvae make differential responses toward conspecifics depending simultaneously on the level of relatedness and the density of the group. Such responses have important implications for social—aggregation decisions and may especially affect the fitness of cannibalistic species.

Complexity of the relationship between life expectancy and overlap of lifespans

Longevity has long been recognised as a key facilitator of reciprocal altruism because repeated cooperation of partners hinges on mutual survival. Although demographic tools can be used to quantify mutual survival and expected overlapping lifespans, studies on the evolutionary theory of cooperation take only limited advantage of demography. Overlap of lifespans depends on variation in survival across ages and can be high or low independently of high or low life expectancies. Here we develop formal demographic measures to study the complex relationships between shared life expectancy of two birth cohort peers, the proportion of their lives that they can expect to overlap, and longevity. We simulate age-specific mortality schedules using a Siler model to reveal how infant and senescent mortality, along with age-independent mortality, affect the relationship between the proportion of life shared and life expectancy. We find that while the proportion of life shared can vary vastly for similar life expectancies, almost all changes to mortality schedules that result in higher life expectancies also result in higher proportions of life shared. A distinct exception occurs if life expectancy increases due to lowering the rate of senescence. In this case the proportion of life shared decreases. Our work shows that almost all selective pressures that result in higher life expectancies also result in a larger proportion of life shared. Therefore, selective forces that extend life also improve the chances that a cooperative system would be stable in terms of reciprocal interactions. Since reciprocal interactions may also reduce mortality and result in a feedback loop with the evolution of longevity, our measures and findings can be used for future cross-species comparisons that aim to disentangle predecessor and successor in the evolution of longevity and cooperation.

Faithful or not: direct and indirect effects of climate on extra-pair paternities in a population of Alpine marmots

Despite being identified an area that is poorly understood regarding the effects of climate change, behavioural responses to climatic variability are seldom explored. Climatic variability is likely to cause large inter-annual variation in the frequency of extra-pair litters produced, a widespread alternative mating tactic to help prevent, correct or minimize the negative consequences of sub-optimal mate choice. In this study, we investigated how climatic variability affects the inter-annual variation in the proportion of extra-pair litters in a wild population of Alpine marmots. During 22 years of monitoring, the annual proportion of extra-pair litters directly increased with the onset of earlier springs and indirectly with increased snow in winters. Snowier winters resulted in a higher proportion of families with sexually mature male subordinates and thus, created a social context within which extra-pair paternity was favoured. Earlier spring snowmelt could create this pattern by relaxing energetic, movement and time constraints. Further, deeper snow in winter could also contribute by increasing litter size and juvenile survival. Optimal mate choice is particularly relevant to generate adaptive genetic diversity. Understanding the influence of environmental conditions and the capacity of the individuals to cope with them is crucial within the context of rapid climate change.

Limited and fitness-neutral effects of resource heterogeneity on sociality in a communally rearing rodent

Contrasting scenarios have been proposed to explain how resource heterogeneity influences group living or sociality. First, sociality may result from individuals in larger groups attaining net fitness benefits by monopolizing access to resources ("resource-defense" hypothesis). Second, sociality may be the fitness-neutral outcome of multiple individuals using a territory with sufficient resources to sustain a group of conspecifics ("resource-dispersion" hypothesis). While previous studies have tended to support the resource-dispersion hypothesis, these analyses have typically examined only 1 or a few predictions, making it difficult to distinguish between the 2 alternatives. We conducted a 4-year field study of Octodon degus to quantify the effects of spatial heterogeneity in food and refuge distributions on group size and 2 components of reproductive success (per capita number of offspring, offspring survival) in this plural breeding and communal rearing rodent. We found only a small effect of heterogeneity of food resources on group size; the effect food resource distribution on group territory size varied across years. Group size did not vary with spatial variation in group territory size and quality. Importantly, there was no covariation between group size and quality of an individual's territory (i.e., a measure of individual access to resources), or between this measure of territory quality and reproductive success, implying no resource-based benefits to social degus. Overall, our results were more consistent with fitness-neutral relationships among spatial heterogeneity of resources, sociality, and territory size. The resource-dispersion hypothesis, however, did not provide a complete explanation for degu socioecology. Se han propuesto distintas hipótesis para explicar cómo la heterogeneidad de los recursos afecta la vida en grupos, o sociabilidad. Esta puede surgir en situaciones donde individuos en grupos grandes se benefician al monopolizar el acceso a recursos (hipótesis de defensa de recursos). Por otra parte, la vida en grupos también puede ser el resultado neutro (en términos de adecuación) de individuos que comparten un territorio con recursos suficientes (hipótesis de dispersión de recursos). Aunque algunos estudios previos han validado la hipótesis de dispersión de recursos, estos solo han evaluado un número limitado de las predicciones de esta hipótesis, lo que ha dificultado distinguir entre esta y otras hipótesis alternativas. Durante un estudio de 4 años cuantificamos los efectos de la heterogeneidad espacial de alimento y distribución de refugios sobre el tamaño de grupo y dos componentes del éxito reproductivo (número per cápita de crías, supervivencia de las crías) en Octodon degus. Se registraron efectos relativamente pequeños de la heterogeneidad espacial del alimento sobre el tamaño de grupo, y variables entre años sobre el tamaño del territorio de cada grupo. El tamaño de grupo no fue afectado por la variación espacial en el tamaño y calidad del territorio de los grupos. No se registró co-variación entre el tamaño de los grupos y la calidad del territorio de cada individuo (una medida individual del acceso a recursos), o entre la calidad del territorio individual y el éxito reproductivo, lo que sugiere ausencia de beneficios derivados del uso social de recursos en degus. En general, los resultados fueron más consistentes con un escenario de efectos neutros de la heterogeneidad espacial de recursos sobre la sociabilidad. Sin embargo, la hipótesis de dispersión de recursos no explicó el conjunto de efectos (o su ausencia) asociados a la socioecología del degu.

Sex-based differences in the adaptive value of social behavior contrasted against morphology and environment

The adaptive nature of sociality has long been a central question in ecology and evolution. However, the relative importance of social behavior for fitness, compared to morphology and environment, remains largely unknown. We assessed the importance of sociality for fitness (lamb production and survival) in a population of mark6d bighorn sheep (Ovis canadensis) over 16 years (n = 1022 sheep-years). We constructed social networks from observations (n = 38,350) of group membership (n = 3150 groups). We then tested whether consistent individual differences in social behavior (centrality) exist and evaluated their relative importance compared to factors known to affect fitness: mass, age, parental effects, and population density. Sheep exhibited consistent individual differences in social centrality. Controlling for maternal carryover effects and age, the positive effect of centrality in a social network on adult female lamb production and survival was equal or greater than the effect of body mass or population density. Social centrality had less effect on male survival and no effect on adult male lamb production or lamb survival. Through its effect on lamb production and survival, sociality in fission-fusion animal societies may ultimately influence population dynamics equally or more than morphological or environmental effects.

Social and ecological factors influencing offspring survival in wild macaques

Premature loss of offspring decreases direct fitness of parents. In gregarious mammals, both ecological and social variables impact offspring survival and may interact with each other in this regard. Although a number of studies have investigated factors influencing offspring loss in mammals, we still know very little on how different factors interact with one another. We therefore investigated fetal and infant mortality in 3 large groups of wild crested macaques (Macaca nigra) over a period of up to 5 years by including potential social causes such as maternal dominance rank, male immigration, between group encounters, and ecological conditions such as rainfall in a multivariate survival analysis using Cox proportional hazards model. Infant but not fetal survival was most impaired after a recent takeover of the alpha-male position by an immigrant male. Furthermore, infant survival probability increased when there was an increase in number of group adult females and rainfall. Fetal survival probability also increased with an increase of these 2 factors, but more in high-ranking than low-ranking females. Fetal survival, unlike that of infants, was also improved by an increase of intergroup encounter rates. Our study thus stresses the importance of survival analyses using a multivariate approach and encompassing more than a single offspring stage to investigate the determinants of female direct fitness. We further provide evidence for fitness costs and benefits of group living, possibly deriving from high pressures of both within- and between-group competition, in a wild primate population.

Reproductive correlates of social network variation in plurally breeding degus (Octodon degus)

Studying the causes and reproductive consequences of social variation can provide insight into the evolutionary basis of sociality. Individuals are expected to behave adaptively to maximize reproductive success, but reproductive outcomes can also depend on group structure. Degus (Octodon degus) are plurally breeding rodents, in which females allonurse indiscriminately. However, communal rearing does not appear to enhance female reproductive success, and larger group sizes are correlated with decreasing per capita pup production. To further investigate mechanisms underlying these patterns, we asked how differences in sex, season and average group reproductive success are related to degu association networks. We hypothesized that if reproductive differences mirror social relationships, then females (core group members) should show stronger and more stable associations than males, and female association strength should be strongest during lactation. We also hypothesized that, at the group level, social cohesion would increase reproductive output, while social conflict would decrease it. Females did have higher association strength and more preferred partners than males, but only during lactation, when overall female associations increased. Females also had more stable preferred social partnerships between seasons. A measure of social cohesion (average association strength) was not related to per capita pup production of female group members, but potential social conflict (heterogeneity of association strengths) was negatively related to per capita pup production of female group members. Our results highlight temporal and multilevel patterns of social structure that may reflect reproductive costs and benefits to females.