Towards an Integrated Concept of Personality in Human and Nonhuman Animals.

Every individual has an idiosyncratic way of feeling, thinking and behaving, which is relatively stable across time and situations. Usually known as Personality, today this phenomenon is recognized in many species, including arthropods, fish, avian or mammals. From an evolutionary perspective, research has shown that personality differences are manifest in distinctive forms of dealing with selective pressures, with consequences for fitness. Despite these facts, the study of personality in animals other than humans is relatively new. Only two decades ago, consistent behavioral individual differences were considered 'noise' around an optimal strategy for behavioral ecologists. Also, psychologists were not interested in animal personality as a consequence of the fear of anthropomorphization and the erroneous belief that humans are unique in nature. Fortunately, this misconception seems already overcome but there are still conceptual issues preventing a unified concept of personality. Throughout this review, we first explore the etymological origins of personality and other terminological issues. We further revise the historical course of the study of personality in humans and other animals, from the perspectives of Psychology and Behavioral Ecology, on the basis of the most used approach, the trait theory. We present the study of nonhuman primates as a paradigmatic example in between both frameworks. Finally, we discuss about the necessity of a unified science of personality.

Homosexual Courtship in Young Wild Capuchin Monkeys: A Case Study.

In primates, many species exhibit same-sex sexual behaviors (SSB), defined as "genital contact or genital manipulation between same-sex individuals." Several sociosexual functions have been proposed, including proceptivity enhancement, receptivity reduction, dominance assertion, practice for heterosexual copulation, tension regulation, reconciliation, and alliance formation. Capuchin monkeys are known for their rich and flexible sexual behavioral repertoire and elaborated courtships. At present, the few reports of SSB in capuchin monkeys (genera Sapajus and Cebus) focused on mounting. Here, we describe the case observed in a population of wild yellow-breasted capuchin monkeys (Sapajus xanthosternos) in which two young males, aged 5-6 years and 19 months, performed a 15-min uninterrupted sequence of courtship behaviors and mounting. Comparing with a previously established ethogram of 20 behaviors typical for heterosexual behavior of tufted capuchins, we show that these males performed 16 of them. Thus, SSBs are already present in the repertoire of young individuals and the practice may serve to create or strengthen bonds. Although same-sex mounting and genital inspection are common in capuchins' play and other social interactions, the almost entire array of courtship behaviors has never been observed in youngsters. Additionally, this example supports the notion that primate (homo)sexual behavior is not limited to genitalia and copulation, since the observed courtship included diverse behaviors different from genital contact. Thus, we propose a broader definition of sexual behavior.

Interações sexuais entre indivíduos do mesmo sexo: um olhar evolucionista / Same-sex sexual interactions: an evolutionary perspective / Interactions sexuelles entre personnes du même sexe: une perspective évolutionniste / Interacciones sexuales entre individuos del mismo sexo: una visión evolucionista

Resumo Sob uma perspectiva evolutiva, as interações sexuais entre indivíduos do mesmo sexo foram por muito tempo consideradas um grande paradoxo. Isso por terem persistido no decorrer das gerações apesar de supostamente não oferecerem benefícios reprodutivos diretos, reduzindo, aparentemente, a aptidão individual. Apesar disso, são comuns em muitas espécies animais. Neste artigo, revisaremos algumas das hipóteses funcionais que tentam resolver esse quebra-cabeça evolutivo. Algumas dessas hipóteses consideram essas interações adaptativas, o que significa que trariam benefícios para os indivíduos. Outras as consideram neutras, derivadas de características realmente vantajosas. Por fim, existem as que consideram essas interações como não-adaptativas e potencialmente prejudiciais aos indivíduos. Ao final, abordaremos uma hipótese revolucionária que, de forma inédita, questiona se as interações sexuais envolvendo exclusivamente indivíduos de sexos diferentes seriam realmente o estado basal do comportamento sexual.

Abstract From an evolutionary point of view, same-sex sexual interactions have long been considered a major paradox. This is because they have persisted throughout generations despite, presumably, not offering direct reproductive benefits and, apparently, reducing individual fitness. Nonetheless, same-sex sexual interactions are common in many animal species. This paper reviews some functional hypotheses that seek to solve this evolutionary puzzle: some consider it adaptative, meaning that these behaviors would bring benefits to individuals; others see it as a neutral by-product of other advantageous characteristics. A third branch understand same-sex sexual interactions to be non-adaptative and potentially deleterious to individuals. Finally, this paper discusses a revolutionary hypothesis that, unprecedently, questions whether sexual interactions involving exclusively individuals of the opposite sex are in fact the basal state of sexual behavior.

Résumé Du point de vue de l'évolution, les interactions sexuelles entre personnes du même sexe ont longtemps été considérées comme un grand paradoxe majeur. En effet, elles ont persisté au fil des générations bien qu'elles n'offrent vraisemblablement pas d'avantages reproductifs directs et qu'elles réduisent apparemment la valeur adaptative individuelle. Néanmoins, sont courantes chez de nombreuses espèces animales. Cet article passe en revue certaines hypothèses fonctionnelles qui cherchent à résoudre cette énigme évolutive : certaines considèrent les interactions comme adaptatives, ce qui signifie que ces comportements apporteraient des avantages aux individus ; d'autres voient les comme un sous-produit neutre d'autres caractéristiques avantageuses. Une troisième branche les comprend comme étant non-adaptatives et potentiellement délétères pour les individus. Enfin, on discute d'une hypothèse révolutionnaire qui, sans précédent, remet en question le fait que les interactions sexuelles impliquant exclusivement des individus du sexe opposé serait l'état ancestral du comportement sexuel.

Resumen Desde una perspectiva evolutiva, las interacciones sexuales entre individuos del mismo sexo han sido consideradas por mucho tiempo como una enorme paradoja. Esto es debido a que han persistido generación tras generación a pesar de, supuestamente, no ofrecer beneficios reproductivos directos, reduciendo, aparentemente, la aptitud individual. Sin embargo, son comunes en muchas especies de animales. En este artículo repasaremos algunas de las hipótesis funcionales que intentan resolver este rompecabezas evolutivo. Algunas de estas hipótesis consideran que estas interacciones son adaptativas, lo que trae benefícios a los individuos. Otras hipótesis las consideran neutras, derivadas de características realmente ventajosas. Mientras que otras consideran estas interacciones como no adaptativas y potencialmente perjudiciales para los individuos. Por último, expondremos una hipótesis revolucionaria que, de manera inédita, cuestiona si las interacciones sexuales que involucran exclusivamente a individuos de diferentes sexos son realmente el estado basal del comportamiento sexual.

Assessing the personality structure of wild capuchin monkeys (Sapajus xanthosternos) using trait rating and behavioral coding.

The study of personality in nonhuman primates has increased substantially, but most studies so far have been conducted with captive animals. In addition, few studies investigated the personality of Neotropical (Platyrrhini) monkeys. If we aim at investigating the ecological and social significance of personality in nonhuman primates, conducting studies of wild populations and covering a wide range of taxa is essential. In this study, we analyzed the personality structure of a wild group of Neotropical monkeys, the yellow-breasted capuchin (Sapajus xanthosternos). We adopted two widespread methods: trait rating, using the Hominoid Personality Questionnaire, and behavioral coding, analyzing 13 behaviors and 3 derived variables. We described 3 traits with trait rating, labeled Openness-Neuroticism, Assertiveness, and Attentiveness-Sociability. We also described 3 traits with behavioral coding, labeled Prosociality, Aggressiveness, and Reactivity to Humans. Comparing both methods we found not only broad convergences between the structures obtained (e.g., both showed prosocial and aggressive traits) but also some differences (e.g., Openness-Neuroticism was not clearly defined with behavioral coding), concluding that combining both methods provided complementary findings. Some socioecological variables seem to influence the expression of personality in captive versus wild living monkeys. For example, in our study, assertive individuals were more vigilant, whereas in the studies in captivity, neurotic individuals were more vigilant. These questions highlight the need for more research in wild conditions and enlarging the number of species and populations studied. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

A longitudinal assessment of behavioral development in wild capuchins: Personality is not established in the first 3 years.

Animal personality is defined as consistent individual differences across time and situations, but little is known about how or when those differences are established during development. Likewise, several studies described the personality structure of adult capuchin monkeys, without assessing the ontogeny of these personality traits. We analyzed the behavioral repertoire of 12 wild infants (9 males, 3 females) yellow-breasted capuchin monkeys (Sapajus xanthosternos), in Una Biological Reserve (Bahia, Brazil). Each infant was observed and filmed weekly from birth until 36 months, through daily focal sampling. We analyzed the behavior of each individual in 10 developmental points. By means of component reduction (principal component analysis), we obtained four behavioral traits: Sociability, Anxiety, Openness, and Activity. We investigated whether there were developmental effects on those traits by fitting regression models for the effect of time on behavioral traits, controlling for monkey identity, sex, and cohort. Sociability (decreasing) and Anxiety (increasing) changed significantly along development. By means of repeatability analysis, we did not find intra-individual consistency across time in those traits, so we cannot discriminate stable personality traits in early ontogeny. Our results show that the personality structure of capuchin monkeys is not established during early development, in agreement with the literature on human personality.

Predatory threat of harpy eagles for yellow-breasted capuchin monkeys in the Atlantic Forest.

We describe seven encounters between different harpy eagle individuals (Harpia harpyja) and a group of yellow-breasted capuchin monkeys (Sapajus xanthosternos) in Una Biological Reserve. These interactions lasted 58 min on average. In each of those encounters, the capuchin monkeys used particular behavioral strategies against the harpy eagle that were not employed in reaction to other aerial predators. We did not observe any successful predation events, but after one of those encounters an infant disappeared from the capuchin group. As a whole, these observations indicate that the presence of harpy eagles in the group's home range increases predation risk for capuchin monkeys. The present report also suggests a reoccupation by H. harpyja of this area, as no previous recent records identify harpy eagle occurrence in Una Biological Reserve.

Efeito do clima sobre a navegação de macacos-prego (Sapajus nigritus) em área de Mata Atlântica / Weather Effects on Navigation Patterns of Capuchin Monkeys (Sapajus nigritus) in the Atlantic Forest

No estudo da cognição espacial de primatas selvagens, a capacidade de representação da localização espacial de objetivos é habitualmente inferida por mudanças no padrão de deslocamento. A maioria das pesquisas nessa área observa se existem variações na linearidade e velocidade, em função do objetivo. Contudo, poucas pesquisas têm estudado se outros fatores poderiam afetar esses padrões, como variáveis climáticas. O objetivo deste trabalho foi verificar se variações em precipitação e temperatura modificam os padrões de deslocamento de um grupo de macacos-prego da Mata Atlântica. Os macacos foram acompanhados por um ano durante as duas estações consideradas para coletar dados comportamentais. Os dados climáticos foram fornecidos pelo INMET e as rotas foram coletadas com tecnologia GPS. Analisaram-se segmentos diários para objetivos espaciais e segmentos sem objetivo. Em cada segmento calculou-se velocidade e linearidade. Os resultados mostraram que existiu pouca influência da chuva nas variáveis controladas. Entretanto, algumas medidas de linearidade foram afetadas significativamente pela temperatura. Por incluir mudanças da distribuição do alimento, a sazonalidade foi mais explicativa de velocidade e linearidade que as variáveis climáticas. Nossos resultados sugerem que mudanças de velocidade e linearidade em deslocamentos para objetivo são indicadores confiáveis de representação de localização espacial.(AU)

In studies of wild primates spatial cognition by means of natural observation, changes in navigation patterns, particularly travel speed and linearity depending on the spatial target, are usually considered as indicative of the ability of representing and locating spatial goals. However, few investigations have considered whether other factors, such as climatic conditions, could be affecting those navigation patterns. Our goal here was to verify if variations on rainfall and temperature can modify the navigation patterns of a black capuchin monkeys group in the Brazilian Atlantic Forest. For collecting behavioural data, the group was followed during a year in both seasons. The National Institute of Meteorology (INMET) provided the weather data and routes were collected with GPS technology. Goal and non-goal daily segments were analyzed. For each segment, travel speed and linearity index were calculated. Results showed that there was little influence of rainfall on the controlled variables. Nevertheless, some measurements of linearity were influenced by temperature. Seasonality was a better predictor of travel speed and linearity than weather conditions due to changes in food distribution. Our results suggest that changes in travel speed and linearity towards goals are good indicators of the representation of spatial locations.(AU)