Harry H. Marshall

Animal personality: what are behavioural ecologists measuring?

The discovery that an individual may be constrained, and even behave sub‐optimally, because of its personality type has fundamental implications for understanding individual‐ to group‐level processes. Despite recent interest in the study of animal personalities within behavioural ecology, the field is fraught with conceptual and methodological difficulties inherent in any young discipline. We review the current agreement of definitions and methods used in personality studies across taxa and systems, and find that current methods risk misclassifying traits. Fortunately, these problems have been faced before by other similar fields during their infancy, affording important opportunities to learn from past mistakes. We review the tools that were developed to overcome similar methodological problems in psychology. These tools emphasise the importance of attempting to measure animal personality traits using multiple tests and the care that needs to be taken when interpreting correlations between personality traits or their tests. Accordingly, we suggest an integrative theoretical framework that incorporates these tools to facilitate a robust and unified approach in the study of animal personality.

Social networks created with different techniques are not comparable

The recent application of social network analysis to animal populations has provided a tool to quantify group dynamics and individual social positions, which may enhance our understanding of the costs and benefits of sociality and the evolution of behavioural strategies within societies. Despite this, uncertainties remain about whether comparisons can be drawn between studies in which different sampling techniques have been used. We compared social networks constructed from two interaction and three proximity techniques that are frequently used in the literature, at both the ego network and global network levels, using data collected annually for two troops of chacma baboons, Papio ursinus, over 3 years. We obtained very different results at both the global and individual levels, demonstrating the clear distinction between networks built using different interaction and proximity techniques. While interaction techniques may be comparable at the whole global level, proximity techniques were not, and we found the opposite at the ego network level: proximity techniques could be compared whereas interaction techniques could not. As there was a clear distinction between the networks created, caution should be taken when using proximity as a proxy for social interactions (and vice versa) in social network studies. Further, our results showed high variation between troops and study seasons, reemphasizing the importance of incorporating temporal change in the analysis of social networks. Researchers should consider the effects of sampling technique on the networks produced when comparing networks created from different techniques.

Evaluating animal personalities: do observer assessments and experimental tests measure the same thing?

The animal personality literature uses three approaches to assess personality. However, two of these methods, personality ratings and experimentation, have been little compared in captivity and never compared in the wild. We assessed the boldness of wild chacma baboons Papio ursinus using both ratings and experimental methods. Boldness was experimentally assessed when individuals were presented with a novel food item during natural foraging. The boldness of the same individuals was rated on a five-point scale by experienced observers. The ratings and experimental assessments of boldness were found to correlate positively and in a linear fashion. When considered categorically the two approaches showed variable agreement depending on the number of categories assigned and the cut-off criteria adopted. We suggest that the variation between approaches arises because each method captures different aspects of personality; ratings consider personality in absolute terms (using predefined criteria) and multiple contexts, while experimental assessments consider personality in relative terms (using experimental scores relative to the population average) and in limited contexts. We encourage animal personality researchers to consider adopting both methodologies in future studies. We also propose that future studies restrict their analyses to continuous data, since the greatest comparability between methods was found with these data. However, if individuals must be categorised, we suggest that researchers either (a) analyse only those individuals categorised as bold or shy by both ratings and experimental approaches or, if these methods cannot be employed simultaneously, (b) do not use approach-specific criteria but choose a cut-off that can be compared by both approaches.

Experimental evidence of impacts of an invasive parakeet on foraging behavior of native birds

Lay Summary Invasive rose-ringed parakeets caused behavioral changes in native garden birds that reduced their feeding rates. Understanding how invasive species impact native species can be complex, especially in urban environments where many other factors are also at play. We therefore used an experiment to disentangle these factors and demonstrate that parakeets are more disruptive than a dominant native competitor.

Personality predicts the propensity for social learning in a wild primate

Social learning can play a critical role in the reproduction and survival of social animals. Individual differences in the propensity for social learning are therefore likely to have important fitness consequences. We asked whether personality might underpin such individual variation in a wild population of chacma baboons (Papio ursinus). We used two field experiments in which individuals had the opportunity to learn how to solve a task from an experienced conspecific demonstrator: exploitation of a novel food and a hidden item of known food. We investigated whether the (1) time spent watching a demonstrator and (2) changes in task-solving behaviour after watching a demonstrator were related to personality. We found that both boldness and anxiety influenced individual performance in social learning. Specifically, bolder and more anxious animals were more likely to show a greater improvement in task solving after watching a demonstrator. In addition, there was also evidence that the acquisition of social information was not always correlated with its use. These findings present new insights into the costs and benefits of different personality types, and have important implications for the evolution of social learning.

Personality predicts decision making only when information is unreliable

Phenotypic plasticity in decision making should be selected for when reliable information on current conditions is available. When current information is unreliable, however, selection should favour unresponsive behavioural phenotypes, which might lead to the emergence of personalities. We tested the hypothesis that personality will affect decision making when information is unreliable, but not when it is reliable. We measured two personality traits, boldness and anxiety, in 55 wild chacma baboons, Papio ursinus , by quantifying responses to a novel food and a mild threat, respectively, in repeated field experiments. To assess decision making under different information reliabilities, we recorded foraging decisions in two contexts. We followed the baboons as they foraged naturally with reliable information about their environment (>8900 decisions) and, to manipulate information reliability experimentally, we performed a large-scale in situ foraging experiment during which we provided the study troops with access to experimental food patches (>10 000 decisions). Importantly, the baboons could not see the food in the experimental patches until close inspection of them, and thus had unreliable information about patch quality. We found plastic foraging decisions in the presence of reliable cues, but personality-dependent decisions in the absence of such cues. Specifically, bold individuals were more likely to produce, and shy individuals scrounge, in the experimental arena but there was no effect of personality on foraging decisions under natural foraging conditions. Our results clarify the importance of information reliability in the evolution of personality and plasticity. These findings also contribute to our understanding of how individuals, and thus populations, might respond to environmental change in the future.

A female signal reflects MHC genotype in a social primate

BackgroundMales from many species are believed to advertise their genetic quality through striking ornaments that attract mates. Yet the connections between signal expression, body condition and the genes associated with individual quality are rarely elucidated. This is particularly problematic for the signals of females in species with conventional sex roles, whose evolutionary significance has received little attention and is poorly understood. Here we explore these questions in the sexual swellings of female primates, which are among the most conspicuous of mammalian sexual signals and highly variable in size, shape and colour. We investigated the relationships between two components of sexual swellings (size and shape), body condition, and genes of the Major Histocompatibility Complex (MHC) in a wild baboon population (Papio ursinus) where males prefer large swellings.ResultsAlthough there was no effect of MHC diversity on the sexual swelling components, one specific MHC supertype (S1) was associated with poor body condition together with swellings of small size and a particular shape. The variation in swelling characteristics linked with the possession of supertype S1 appeared to be partially mediated by body condition and remained detectable when taking into account the possession of other supertypes.ConclusionsThese findings suggest a pathway from immunity genes to sexual signals via physical condition for the first time in females. They further indicate that mechanisms of sexual selection traditionally assigned to males can also operate in females.

Exploring Foraging Decisions in a Social Primate Using Discrete-Choice Models

There is a growing appreciation of the multiple social and nonsocial factors influencing the foraging behavior of social animals but little understanding of how these factors depend on habitat characteristics or individual traits. This partly reflects the difficulties inherent in using conventional statistical techniques to analyze multifactor, multicontext foraging decisions. Discrete-choice models provide a way to do so, and we demonstrate this by using them to investigate patch preference in a wild population of social foragers (chacma baboons Papio ursinus). Data were collected from 29 adults across two social groups, encompassing 683 foraging decisions over a 6-month period and the results interpreted using an information-theoretic approach. Baboon foraging decisions were influenced by multiple nonsocial and social factors and were often contingent on the characteristics of the habitat or individual. Differences in decision making between habitats were consistent with changes in interference-competition costs but not with changes in social-foraging benefits. Individual differences in decision making were suggestive of a trade-off between dominance rank and social capital. Our findings emphasize that taking a multifactor, multicontext approach is important to fully understand animal decision making. We also demonstrate how discrete-choice models can be used to achieve this.

Reproductive competition triggers mass eviction in cooperative banded mongooses

In many vertebrate societies, forced eviction of group members is an important determinant of population structure, but little is known about what triggers eviction. Three main explanations are: (i) the reproductive competition hypothesis, (ii) the coercion of cooperation hypothesis, and (iii) the adaptive forced dispersal hypothesis. The last hypothesis proposes that dominant individuals use eviction as an adaptive strategy to propagate copies of their alleles through a highly structured population. We tested these hypotheses as explanations for eviction in cooperatively breeding banded mongooses (Mungos mungo), using a 16-year dataset on life history, behaviour and relatedness. In this species, groups of females, or mixed-sex groups, are periodically evicted en masse. Our evidence suggests that reproductive competition is the main ultimate trigger for eviction for both sexes. We find little evidence that mass eviction is used to coerce helping, or as a mechanism to force dispersal of relatives into the population. Eviction of females changes the landscape of reproductive competition for remaining males, which may explain why males are evicted alongside females. Our results show that the consequences of resolving within-group conflict resonate through groups and populations to affect population structure, with important implications for social evolution.

Explaining negative kin discrimination in a cooperative mammal society

Significance Kin selection theory predicts that animals will direct altruism toward closer genetic relatives and aggression toward more distantly related individuals. Our 18-y study of wild banded mongooses reveals that, unusually, dominant individuals target females who are more closely related to them for violent eviction from the group. This puzzling result can be explained by selection for unrelated individuals to resist eviction and for related individuals to submit more easily. In support of this idea, we show that kin are targeted for aggression only when individuals are capable of resisting. Our results suggest that, where potential victims can oppose aggression, the usual predictions of kin selection theory can be reversed. Kin selection theory predicts that, where kin discrimination is possible, animals should typically act more favorably toward closer genetic relatives and direct aggression toward less closely related individuals. Contrary to this prediction, we present data from an 18-y study of wild banded mongooses, Mungos mungo, showing that females that are more closely related to dominant individuals are specifically targeted for forcible eviction from the group, often suffering severe injury, and sometimes death, as a result. This pattern cannot be explained by inbreeding avoidance or as a response to more intense local competition among kin. Instead, we use game theory to show that such negative kin discrimination can be explained by selection for unrelated targets to invest more effort in resisting eviction. Consistent with our model, negative kin discrimination is restricted to eviction attempts of older females capable of resistance; dominants exhibit no kin discrimination when attempting to evict younger females, nor do they discriminate between more closely or less closely related young when carrying out infanticidal attacks on vulnerable infants who cannot defend themselves. We suggest that in contexts where recipients of selfish acts are capable of resistance, the usual prediction of positive kin discrimination can be reversed. Kin selection theory, as an explanation for social behavior, can benefit from much greater exploration of sequential social interactions.