Are animal personality, body condition, physiology and structural size integrated? A comparison of species, populations and sexes, and the value of study replication

A major question in behavioural ecology is why behaviour, physiology and morphology are often integrated into syndromes. In great tits, Parus major, for example, explorative males are larger (vs. smaller) and leaner (vs. heavier) compared to less explorative individuals. Unfortunately, considerable debate exists on whether patterns found in specific studies are replicable. This debate calls for study replication among species, populations and sexes. We measured behavioural (exploration), physiological (breathing rate) and morphological traits (body mass, tarsus length, wing length, bill length) in two species (great vs. blue tits Cyanistes caeruleus), two populations (Forstenrieder Park vs. Starnberg) and two sexes (males vs. females). We then tested whether the same pattern of integration characterized all unique combinations of these three biological categories (hereafter called datasets). We used a multi-year repeated measures set-up to estimate among-individual trait correlation matrices for each dataset. We then used structural equation modelling to test for size-dependent behaviour and physiology, size-corrected (i.e. size-independent) behaviour-physiology correlations and size-corrected body mass-dependent behaviour and physiology. Finally, we used meta-analyses to test which structural paths were generally (vs. conditionally) supported (vs. unsupported). We found general and consistent support for size-dependent physiology and size-corrected body mass-dependent physiology across datasets: faster breathers were smaller but heavier for their size. Unexpectedly, condition-dependent behaviour was not supported: explorative birds were neither leaner, nor was this relationship heterogeneous across datasets. All other hypothesized patterns were dataset-specific: the covariance between size and behaviour, and between behaviour and physiology differed in sign between datasets, and both were, on average, not supported. This heterogeneity was not explained by any of our moderators: species, population or sex. The specific pattern of size- and condition-dependent physiology reported for a unique combination of species, population, and sex, thus generally predicted those in others. Patterns of size- or condition-dependent behaviour (i.e. ‘personality’), or behaviour-physiology syndromes reported in specific datasets, by contrast, did not. These findings call for studies revealing the ecological background of this variation and highlight the value of study replication to help understand whether patterns of phenotypic integration reported in one study can be generalized

The consequences and underlying mechanisms of animal personality in dunnocks (Prunella modularis)

In behavioural ecology, the research of animal personality, that is, consistent between individual differences in behaviour, has attracted a considerable amount of attention during the last two decades. While past research has mainly focused on the description of personality traits in animal populations, we still know very little about the ecological and evolutionary relevance, and the mechanisms maintaining such personality traits. This thesis seeks out to increase our understanding of the consequences and underlying mechanisms of animal personality. I used observational data to examine the long-term stability of four behavioural traits (boldness, provisioning, activity and vigilance) in a wild population of dunnocks (Prunella modularis; Chapter 2). On the one hand, dunnocks showed moderate to high repeatability in flight-initiation distance (FID) and parental provisioning over the entire study period of three years and across different age classes (age 1 to 6 years). Repeatability estimates of males and females differed in provisioning behaviour from each other. On the other hand, dunnocks displayed low levels of repeatability for activity and vigilance. Despite this, no behavioural syndromes were found, suggesting that selection did not favour specific combinations of the four investigated traits. I also investigated which role personality traits play in the spatial distribution of behavioural phenotypes (Chapter 3). Specifically, I tested empirically tested whether personality or habituation is responsible for the non random distribution of shy and bold individuals. My results suggest that an individual’s personality type largely determines the habitat in which an individual settles. These findings highlight the role personality plays in shaping population structure and lending support to the theory of personality-mediated speciation.Using a molecular approach, I investigated the underlying genetic basis of animal personality (Chapter 4). By comparing a native (United Kingdom, UK) and an introduced population (New Zealand, NZ) of dunnocks, I showed that the introduced population has lower genetic diversity in two ‘personality genes’, DRD4 and SERT, than the UK population. Additionally, I found 38 significant associations between polymorphisms in DRD4 and SERT, and two repeatable behavioural traits; FID and mating status. My results indicate that anthropogenic-caused introductions may influence the genetic diversity of ‘personality genes’, and also corroborate the genetic influence of DRD4 and SERT on personality traits. Finally, I employed meta-analyses (Chapter 5) to assess which of the two proposed physiological traits, hormone levels or metabolic rates is more likely the underlying mechanism shaping personality differences. Results of these analyses suggested that variation in metabolic rates is one of the key drivers regulating between-individual differences in behaviour. On the other hand, hormone levels seem to be more likely to control for variation at the within-individual level. Taken together, my thesis makes an important contribution to our understanding of the ecological and evolutionary consequences and underlying mechanisms of animal personality. Further, my work highlights the importance of studying personality traits in wild populations

Visitor survey February 2015

To quantify the levels of human disturbance in the study area, we counted the number of visitors in each of the 141 squares that covered our study area. In total, we conducted three surveys (February 2014, August 2014, February 2015), each over a period of 24 consecutive days

Flight-initiation-distance, age, and sampling interval data

Flight-initiation distance measurements, age, and sampling interval of 99 individuals used in 'Personality-matching habitat choice, rather than behavioural plasticity, is a likely driver of a phenotype-environment covariance'

Visitor survey August 2014

To quantify the levels of human disturbance in the study area, we counted the number of visitors in each of the 141 squares that covered our study area. In total, we conducted three surveys (February 2014, August 2014, February 2015), each over a period of 24 consecutive days

Dominance relationships and coalitionary aggression against conspecifics in female carrion crows

Cooperation is a prevailing feature of many animal systems. Coalitionary aggression, where a group of individuals engages in coordinated behaviour to the detriment of conspecific targets, is a form of cooperation involving complex social interactions. To date, evidence has been dominated by studies in humans and other primates with a clear bias towards studies of male-male coalitions. We here characterize coalitionary aggression behaviour in a group of female carrion crows consisting of recruitment, coordinated chase, and attack. The individual of highest social rank liaised with the second most dominant individual to engage in coordinated chase and attack of a lower ranked crow on several occasions. Despite active intervention by the third most highly ranked individual opposing the offenders, the attack finally resulted in the death of the victim. All individuals were unrelated, of the same sex, and naive to the behaviour excluding kinship, reproduction, and social learning as possible drivers. Instead, the coalition may reflect a strategy of the dominant individual to secure long-term social benefits. Overall, the study provides evidence that members of the crow family engage in coordinated alliances directed against conspecifics as a possible means to manipulate their social environment.</p

Visitor survey February 2014

To quantify the levels of human disturbance in the study area, we counted the number of visitors in each of the 141 squares that covered our study area. In total, we conducted three surveys (February 2014, August 2014, February 2015), each over a period of 24 consecutive days

Territories and assigned squares

For each breeding season, individuals were assigned to a grid of 141 squares covering the whole study area

Data from: Personality-matching habitat choice, rather than behavioural plasticity, is a likely driver of a phenotype–environment covariance

An emerging hypothesis of animal personality posits that animals choose the habitat that best fits their personality, and that the match between habitat and personality can facilitate population differentiation, and eventually speciation. However, behavioural plasticity and the adjustment of behaviours to new environments have been a classical explanation for such matching patterns. Using a population of dunnocks (Prunella modularis), we empirically tested whether personality or behavioural plasticity is responsible for the non-random distribution of shy and bold individuals in a heterogeneous environment. We found evidence for bold individuals settling in areas with high human disturbance, but also that birds became bolder with increasing age. Importantly, personality primarily determines the distribution of individuals, and behavioural adjustment over time contributes very little to the observed patterns. We cannot, however, exclude a possibility of very early behavioural plasticity (a type of developmental plasticity) shaping what we refer to as ‘personality’. Nonetheless, our findings highlight the role personality plays in shaping population structure, lending support to the theory of personality-mediated speciation. Moreover, personality-matching habitat choice has important implications for population management and conservation