Kinship Discrimination and Effects on Social Rank and Aggressiveness Levels in Iberian Red Deer Hinds

Social networks of reintroduced Przewalski's horses in the Great Gobi B Strictly Protected Area (Mongolia)

Analyzing social networks is a powerful tool for understanding the ecology of social species. While most studies focus on the role of each group member, few compare groups with different characteristics. The current population of Przewalski's horses Equus ferus przewalskii at the Great Gobi B Strictly Protected Area (Mongolia) includes groups of wild-born and captive-bred individuals with different experiences with the area (acclimatizing, long-term reintroduced, and wild-born), therefore serving as an ideal natural behavioral lab. We filmed 11 groups for 141.5 hours in summer 2018 (July), late spring 2019 (May, June), and autumn 2019 (September, October). Affiliative and agonistic interactions were recorded, and social networks were created. We tested the influence of origin, experience, season, sex, age, relative time belonging to the group, relatedness, and dominance rank on different network indices at the individual and group levels. We found that groups with greater experience in the area are generally better connected than members of the newly formed groups. However, these strong networks were created by wild-born individuals with very low interaction rates. On the contrary, inexperienced groups composed of captive-bred individuals displayed many interactions but created weak social networks. The results show a trend of behavioral transition from acclimatizing through long-term reintroduced to wild-born groups, supporting that the newly formed groups of released Przewalski's horses need time to display the typical social behavior patterns of wild-born individuals. Long-term monitoring of released Przewalski's horses is recommended to promote the success of this reintroduction program.

Pelt Biting as a Practical Indicator of Social and Environment Stress in Farmed Red Deer

Simple Summary

Agonistic behavioural interactions play a decisive role in the competition for food, space, mating opportunities, and establishing social rank. We propose the use of the number of bites on the pelt of red deer as an index of agonistic interactions between group members. Using behavioural data from a 14-year time series of a captive population of Iberian red deer (Cervus elaphus), we found that deer that were of higher social rank, heavier, living in smaller groups, or under no heat stress conditions suffer less pelt bites than those of lower social rank, lighter, living in bigger groups, or under heat stressing conditions. Hinds that gave birth earlier in the parturition period suffered less pelt biting than those that gave birth around the peak of the parturition season. Pelt biting is useful to identify management situations in which deer welfare could be at stake.

Abstract

Agonistic behavioural interactions play a decisive role in the competition for food, space, mating opportunities, and establishing social rank. We used pelt biting (number of bites on an animal’s body) as a proxy for assessing the intensity of agonistic animal interactions and how it responded to social, population, and heat stress factors. We modelled a 14-year time series of pelt biting records and observational data of agonistic interactions on a population of captive Iberian red deer (Cervus elaphus). We found that (i) the higher the social rank of deer, the lower the number of pelt bites received; (ii) increasing heat stress conditions caused deer to suffer more pelt bites; (iii) males received more bites than females; (iv) the heavier the deer, the lower the number of bites on their bodies; (v) the bigger the group, the more bites exhibited on its members; (vi) deer 5–6 years old suffered greater rate of pelt biting than younger or older deer; and (vii) hinds that gave birth earlier in the parturition period suffered less pelt biting than those that gave birth around the peak of the parturition season (p < 0.01 for all effects). Pelt biting is useful to predict management situations in which deer welfare could be at stake.

Third-party conflict interventions are kin biased in captive white-lipped peccaries (Mammalia, Tayassuidae)

Third-party interventions may regulate conflicts to reduce aggression and promote cohesion amongst group members, but are rarely documented in ungulates. The white-lipped peccary (Tayassu pecari) lives in mixed-sex herds of hundreds of individuals in Neotropical forests, which are likely to benefit from mechanisms that sustain social cohesiveness. We examined third-party conflict interventions between individuals in captive groups of white-lipped peccaries. During a period of 60 days, we recorded agonistic interactions and occurrences of third-party conflict interventions, and estimated the genetic relatedness between the individuals involved using multilocus microsatellite genotypes. Most third-party conflict interventions were by the dominant male of each group, resulting in conflict termination 100% of the time. Our results also revealed that white-lipped peccaries favour their closest relatives and that individuals showed lower levels of aggression towards kin than to non-kin, and interventions on behalf of kin were more frequent than on behalf of non-kin. Our findings support the idea that genetic relatedness is fundamental in both social structure and third-party conflict interventions in this species, allowing us to suggest that kin selection could have a key role in the evolution of social behaviour of white-lipped peccaries.

Different maternal investment strategies for male and female calves in a polygynous mammal

Maternal effects occur when the phenotype of the mother influences that of the young to the detriment of her survival, growth or fitness. The investment of the mother can be affected by maternal body condition and/or experience. Trivers-Willard Hypothesis (TWH) and Local Resource Competition Hypothesis (LRCH) are the main hypotheses used to explain bias in birth sex-ratios in mammals, as well as for sex-biased maternal investment. Both hypotheses suggest that a different amount of investment must be expected according to the sex of the young. However, recent studies suggest that these differences are not in quantity but in the strategies: mechanisms and objectives may differ for each sex. We studied how maternal characteristics (age, body mass, body condition, and dominance status) influence relevant aspects of the birth and early growth of the calf (birth date, birth body mass, body mass at weaning, and body condition at weaning) separately for each sex; and how that investment is mediated by milk production and composition (lactose, fat, and protein). One hundred eighty-eight newborns from 75 captive red deer hinds aged from 2 to 19 years were analyzed. The main differential investment observed was related to birth date: when producing a female, hinds give birth earlier in the season only if they have a good body condition; however, when gestating a male it is the older hinds those which deliver earlier. Subsequently, milk production and composition are correlated with birth body mass in female calves, but to weaning body mass in males. Thus, only hind body mass affects the weaning body mass of female calves, compared with age and hind body mass in males. These results suggest that while TWH fits the maternal investment strategy found for male calves, it is LRCH which correlates with the maternal investment patterns observed for females.

The social network structure of a semi-free roaming European bison herd (Bison bonasus)

The use of social network analysis to better understand animal behaviour has led to an increase in the number of studies on this topic, particularly for species management and conservation as well as the welfare of captive animals. The current knowledge of social organization in the European bison (Bison bonasus) is still largely based on descriptions of group compositions, most of which were obtained during opportunistic field observations. However, the numerous conservation programs for this species can only implement effective management decisions after the analysis of its social structures. For instance, the removal of a key individual can disturb the social stability of a group and thus indirectly affect the fitness of group members. This is the first study that uses social network analysis to examine the social structure of a semi-free ranging bison herd (N = 14). Closest neighbour associations are used to calculate the eigenvector centrality and individual social strength of each animal. These two indices are combined after a principal component analysis (PCA) to form the Sociability variable, which was then tested for correlations with age, dominance rank, number of matrilines and reproductive status (lactating vs non-lactating). Results reveal strong group cohesion, with a close association of individuals belonging to the same matriline within the herd. The cumulative distribution of the eigenvector centralities follows a linear function, meaning that no individual has a highly central position compared to its congeners. Finally, a high Sociability value was not correlated to age, dominance rank or number of matrilines, but was dependent on the reproductive status of females. These results indicate the necessity to consider the social welfare of animals, for instance by taking matrilineal relationships into account when making bison groups management decisions.

Social rank affects the haematologic profile in red deer hinds

We studied the effects of social rank on the haematologic profile in a herd of 24 female Iberian red deer hinds. Social rank hierarchy was determined and blood samples were taken and analysed. After adjusting for age and body mass, dominance ranking showed a significant negative effect (ie, lower values in dominant hinds) on white blood cell (WBC) count, haemoglobin and haematocrit. Our results are similar to those reported for stressed individuals due to physical immobilisation, but do not support the predicted enhanced erythropoiesis due to higher levels of androgens. The results for WBC numbers may also reflect that subordinate hinds must allocate a higher amount of resources to immunity as a result of injuries incurred from dominant hinds, while simultaneously facing restricted access to food sources. For red blood cell (RBC) counts, the results may be due to subordinate hinds likely needing increased haematocrit and haemoglobin levels for fast flight responses. Our data show that social rank influences haematologic profile, and thus it should be considered when correctly interpreting blood analyses in social cervid species.

The importance of the altricial - precocial spectrum for social complexity in mammals and birds - a review

Various types of long-term stable relationships that individuals uphold, including cooperation and competition between group members, define social complexity in vertebrates. Numerous life history, physiological and cognitive traits have been shown to affect, or to be affected by, such social relationships. As such, differences in developmental modes, i.e. the ‘altricial-precocial’ spectrum, may play an important role in understanding the interspecific variation in occurrence of social interactions, but to what extent this is the case is unclear because the role of the developmental mode has not been studied directly in across-species studies of sociality. In other words, although there are studies on the effects of developmental mode on brain size, on the effects of brain size on cognition, and on the effects of cognition on social complexity, there are no studies directly investigating the link between developmental mode and social complexity. This is surprising because developmental differences play a significant role in the evolution of, for example, brain size, which is in turn considered an essential building block with respect to social complexity. Here, we compiled an overview of studies on various aspects of the complexity of social systems in altricial and precocial mammals and birds. Although systematic studies are scarce and do not allow for a quantitative comparison, we show that several forms of social relationships and cognitive abilities occur in species along the entire developmental spectrum. Based on the existing evidence it seems that differences in developmental modes play a minor role in whether or not individuals or species are able to meet the cognitive capabilities and requirements for maintaining complex social relationships. Given the scarcity of comparative studies and potential subtle differences, however, we suggest that future studies should consider developmental differences to determine whether our finding is general or whether some of the vast variation in social complexity across species can be explained by developmental mode. This would allow a more detailed assessment of the relative importance of developmental mode in the evolution of vertebrate social systems.

Pre-orbital gland opening during aggressive interactions in rusa deer (Rusa timorensis)

The opening of the preorbital gland in cervids has a visual meaning and is frequently associated with agonistic and/or stress related situations. Apart from in red deer, this behaviour has scarcely been studied and the range of situations when it may occur remains unclear. In this study we report the unusual case of preorbital gland opening in rusa deer, Rusa timorensis, associated to direct aggressive agonistic interaction (biting/kicking) between two adult hinds. This case observed in Tierpark Berlin (Germany) is the first one ever recorded in female-female interactions in cervids. Preorbital gland opening was also studied in 116 social interactions in Plzeň Zoo (Czech Republic). Preorbital gland opening by the dominant adult male was twice observed with relation to alert behaviour, which is also rare. In order to contextualise our observations we summarise the current knowledge about the behaviour associated with preorbital gland opening in R. timorensis and in cervids in general.

Social dominance is associated with individual differences in heart rate and energetic response to food restriction in female red deer

Energy expenditure is a key mechanism underlying animal ecology, yet why individuals often differ in metabolic rate even under identical conditions remains largely unexplained. Individual variation in metabolism might be explained by correlations with other behavioral and physiological traits, with individual syndromes having environment- or state-dependent costs and benefits to fitness. We tested whether social rank within herds of female red deer is associated with individual differences in resting heart rate, an index of metabolic rate, and energetic response to monthly periods of food restriction during winter in a large outdoor enclosure near Vienna, Austria. Social rank had a strong positive effect on average daily heart rate, independent of the effects of food intake, air temperature, body temperature, and body mass. Subordinate individuals had lower heart rates than dominants, and consequently they suffered lower rates of body mass loss during periods of restricted pellet food supply. A greater capacity to minimize energy requirements might benefit the survival of subdominant female red deer during periods of negative energy balance in winter. Our study provides empirical support in a large mammal for linkages in behavior and metabolism within individuals that have environment-dependent consequences to the energy budget.

Benefits for dominant red deer hinds under a competitive feeding system: food access behavior, diet and nutrient selection

Social dominance is widely known to facilitate access to food resources in many animal species such as deer. However, research has paid little attention to dominance in ad libitum access to food because it was thought not to result in any benefit for dominant individuals. In this study we assessed if, even under ad libitum conditions, social rank may allow dominant hinds to consume the preferred components of food. Forty-four red deer hinds (Cervus elaphus) were allowed to consume ad libitum meal consisting of pellets of sunflower, lucerne and orange, and seeds of cereals, corn, cotton, and carob tree. The meal was placed only in one feeder, which reduced accessibility to a few individuals simultaneously. During seven days, feeding behavior (order of access, time to first feeding bout, total time spent feeding, and time per feeding bout) were assessed during the first hour. The relative abundance of each meal component was assessed at times 0, 1 and 5 h, as well as its nutritional composition. Social rank was positively related to the amount of time spent feeding during the 1(st) h (P = 0.048). Selection indices were positively correlated with energy (P = 0.018 during the 1(st) h and P = 0.047 from 1(st) to 5(th)) and fat (only during the 1(st) h; P = 0.036), but also negatively with certain minerals. Thus, dominant hinds could select high energy meal components for longer time under an ad libitum but restricted food access setting. Selection indices showed a higher selectivity when food availability was higher (1(st) hour respect to 1(st) to 5(th)). Finally, high and low ranking hinds had longer time per feeding bout than mid ones (P = 0.011), suggesting complex behavioral feeding tactics of low ranking social ungulates.

Direct versus indirect effects of social rank, maternal weight, body condition and age on milk production in Iberian red deer ( Cervus elaphus hispanicus)

Social rank in cervids and other mammals is not entirely predicted by body weight, but in most cases influences access to food directly. Milk provisioning depends on maternal weight and on daily food intake. Usually, body weight, body condition, age and social rank are inter-correlated making it very difficult to discern the relative importance of each variable to milk production. This study used path analysis to assess direct versus indirect effects of these variables on milk production of 62 Iberian red deer hinds (Cervus elaphus hispanicus). Once the known direct effects of body weight and body condition were set as fixed, hind age and social rank did not affect milk production directly. In contrast, they exerted an indirect influence through the correlation both with hind body weight and body condition. Body weight exerted an effect on milk production nearly twice as great as that of body condition. This study shows, for the first time in a wild mammal, the relative importance of social rank, body weight, body condition and age in affecting milk production ability.

Kin in space: social viscosity in a spatially and genetically substructured network

Population substructuring is a fundamental aspect of animal societies. A growing number of theoretical studies recognize that who-meets-whom is not random, but rather determined by spatial relationships or illustrated by social networks. Structural properties of large highly dynamic social systems are notoriously difficult to unravel. Network approaches provide powerful ways to analyse the intricate relationships between social behaviour, dispersal strategies and genetic structure. Applying network analytical tools to a colony of the highly gregarious Galápagos sea lion (Zalophus wollebaeki), we find several genetic clusters that correspond to spatially determined 'network communities'. Overall relatedness was low, and genetic structure in the network can be interpreted as an emergent property of philopatry and seems not to be primarily driven by targeted interactions among highly related individuals in family groups. Nevertheless, social relationships between directly adjacent individuals in the network were stronger among genetically more similar individuals. Taken together, these results suggest that even small differences in the degree of relatedness can influence behavioural decisions. This raises the fascinating prospect that kin selection may also apply to low levels of relatedness within densely packed animal groups where less obvious co-operative interactions such as increased tolerance and stress reduction are important.

Development of body condition in hinds of Iberian red deer during gestation and its effects on calf birth weight and milk production

Reproductive effort affects body reserves and subsequent ability to reproduce. In fact, the energy costs of gestation and lactation in hinds of red deer have a marked effect on maternal condition. The objectives of this study were to examine the development of hind monthly body condition during gestation in relation to reproductive rest, age and age class, just as its effects on total milk yield and calf birth weight. Eighty hinds of Iberian red deer were used as subjects during 2 years of study. They had ad libitum access to food and water. Animals were weighed weekly, and body condition was individually assessed. Milking was carried out under anesthesia with a milking machine followed by hand milking to collect the remaining milk. Age and reproductive rest influenced body condition, improving with age (coefficient: 0.10+/-0.01; P<0.001) and reproductive rest (mean+/-SEM, 3.75+/-0.05 vs. 3.25+/-0.02, with and without rest respectively; P<0.001). Hind age correlated positively with her body condition (R=0.62, P<0.001), however, when age class was included in the model, age was not significant. The greater the age class (up to age class 4) the greater the body condition; however, hinds of age class 5 had a lower body condition, but no significant differences were observed. Development of the body condition during gestation was different to age class 1 with respect to the others, just as between hinds that rested the preceding year and those that did not.