Julien G. A. Martin

Male personality, life‐history strategies and reproductive success in a promiscuous mammal

Recent theoretical work suggests that personality is a component of life history, but links between personality and either age‐dependent reproductive success or life‐history strategy are yet to be established. Using quantitative genetic analyses on a long‐term pedigree we estimated indices of boldness and docility for 105 bighorn sheep rams (Ovis canadensis), born between 1983 and 1999, and compared these indices to their reproductive history from 2 years of age until death. Docility and boldness were highly heritable and negatively genetically correlated. Docile and bold rams survived longer than indocile and shy rams. Docility and boldness had a weak negative effect on reproductive success early in life, but a strong positive effect on older rams. Our findings highlight an important role of personality on reproductive success and suggest that personality could be an important component of life‐history strategy.

Animal temperament and human disturbance: Implications for the response of wildlife to tourism

Studies on the response of wildlife to human disturbance generally focus on demographic changes or on physiological and behavioural modifications directly related to stress response. Yet fewer studies have explored whether the distribution of individual animals in response to human disturbance is influenced by temperament. Temperament represents the consistency of responses of individuals in reaction to novel or challenging situations. Individuals are thus assumed to express highly consistent behaviour-hormonal response under specific stress conditions. In this study, we investigate the relations between exploration, grooming-scanning continuum, emotionality, and docility of individual Eastern chipmunks (Tamias striatus) and location of their burrow respective to frequentation by humans. We then assess the relationship between cortisol accumulated in the hair and both temperament and frequentation by humans. Explorative or docile chipmunks were more common in frequented areas. Hair cortisol increased with docility, but was not related to human frequentation. These results indicate that temperament may cause animals to distribute themselves in a non-random way in response to human disturbance. Integrating temperament into studies of the stress response of wildlife to humans could therefore help us understand the impact of tourism on wildlife.

Development of boldness and docility in yellow-bellied marmots

Personality traits are important because they can affect individual survival as well as how a population may respond to environmental change. How these traits arise, whether they are maintained throughout ontogeny, and how environmental factors differentially affect them throughout life is poorly understood. Understanding these pathways is important for determining the function and evolution of animal personality. We examined the development of two commonly studied personality traits, boldness and docility, in a long-term study of yellow-bellied marmots, Marmota flaviventris. Using data collected between 2002 and 2011, we quantified the repeatability within three age groups (juveniles, yearlings and adults), the correlation between age classes, and the behavioural syndromes of these two traits within the three life stages. We quantified boldness through flight initiation distance (FID) tests, and we quantified docility through marmots’ response to being trapped. We found that boldness was repeatable only in yearlings, but docility was repeatable in all age classes. We also found that juvenile docility predicted later docility. We also found no behavioural syndrome between boldness and docility in any life stage. This suggests an adaptive hypothesis: that these personality traits develop independently and at potentially age-appropriate times. Thus, the development of personality traits may facilitate animal’s coping with age-dependent requirements and constraints.

Heritable victimization and the benefits of agonistic relationships

Here, we present estimates of heritability and selection on network traits in a single population, allowing us to address the evolutionary potential of social behavior and the poorly understood link between sociality and fitness. To evolve, sociality must have some heritable basis, yet the heritability of social relationships is largely unknown. Recent advances in both social network analyses and quantitative genetics allow us to quantify attributes of social relationships and estimate their heritability in free-living populations. Our analyses addressed a variety of measures (in-degree, out-degree, attractiveness, expansiveness, embeddedness, and betweenness), and we hypothesized that traits reflecting relationships controlled by an individual (i.e., those that the individual initiated or were directly involved in) would be more heritable than those based largely on the behavior of conspecifics. Identifying patterns of heritability and selection among related traits may provide insight into which types of relationships are important in animal societies. As expected, we found that variation in indirect measures was largely explained by nongenetic variation. Yet, surprisingly, traits capturing initiated interactions do not possess significant additive genetic variation, whereas measures of received interactions are heritable. Measures describing initiated aggression and position in an agonistic network are under selection (0.3 < |S| < 0.4), although advantageous trait values are not inherited by offspring. It appears that agonistic relationships positively influence fitness and seemingly costly or harmful ties may, in fact, be beneficial. Our study highlights the importance of studying agonistic as well as affiliative relationships to understand fully the connections between sociality and fitness.

Heritability of anti-predatory traits: vigilance and locomotor performance in marmots

Animals must allocate some proportion of their time to detecting predators. In birds and mammals, such anti‐predator vigilance has been well studied, and we know that it may be influenced by a variety of intrinsic and extrinsic factors. Despite hundreds of studies focusing on vigilance and suggestions that there are individual differences in vigilance, there have been no prior studies examining its heritability in the field. Here, we present one of the first reports of (additive) genetic variation in vigilance. Using a restricted maximum likelihood procedure, we found that, in yellow‐bellied marmots (Marmota flaviventris), the heritability of locomotor ability (h2 = 0.21), and especially vigilance (h2 = 0.08), is low. These modest heritability estimates suggest great environmental variation or a history of directional selection eliminating genetic variation in these traits. We also found a significant phenotypic (rP = −0.09 ± 0.04, P = 0.024) and a substantial, but not significant, genetic correlation (rA = −0.57 ± 0.28, P = 0.082) between the two traits (slower animals are less vigilant while foraging). We found no evidence of differential survival or longevity associated with particular phenotypes of either trait. The genetic correlation may persist because of environmental heterogeneity and genotype‐by‐environment interactions maintaining the correlation, or because there are two ways to solve the problem of foraging in exposed areas: be very vigilant and rely on early detection coupled with speed to escape, or reduce vigilance to minimize time spent in an exposed location. Both strategies seem to be equally successful, and this ‘locomotor ability‐wariness’ syndrome may therefore allow slow animals to compensate behaviourally for their impaired locomotor ability.

Bighorn Ewes Transfer the Costs of Reproduction to Their Lambs

Several studies of large mammals report no direct reproductive costs for females. Individual heterogeneity may hide fitness costs of reproduction, but mothers could also transfer some costs to their offspring. Using data on 442 lambs weaned by 146 bighorn sheep (Ovis canadensis) ewes at Ram Mountain, Alberta, we studied how reproductive effort varied with environmental and maternal conditions. During summer, lactating ewes should gain enough mass to survive the winter and to support their next gestation, while nursing their current lamb. We measured reproductive effort as summer mass gain by lambs corrected for maternal mass in June and maternal mass gain during summer. Females lowered their reproductive effort when population density increased and if they had weaned a lamb the previous year. A reduction in reproductive effort led to lower winter survival by lambs. Bighorn ewes have a conservative reproductive tactic and always favor their own body condition over that of their lambs. When resources are limited, ewes appear to transfer reproductive costs to their lambs, as expected from the much greater relative fitness consequences of a reduction in maternal than in offspring survival.

Determinants and life-history consequences of social dominance in bighorn ewes

Studies of social rank in female ungulates consistently suggest that dominance increases with age, perhaps because dyadic relationships are established early in life, when the older female is always larger than the younger one. This relationship then remains unchanged, even if for fully grown adults size and age are not correlated, suggesting that typically female ungulates normally gain little from being dominant. In contrast, social interactions among 64 marked known-age bighorn sheep ewes (Ovis canadensis) over 3 summers at Ram Mountain, Alberta, Canada, suggest that the effect of age on social rank weakened substantially for ewes older than 6 years. Mass was strongly related to rank for ewes age 7 years and older, whereas horn size had no effect on dominance. Once they reach asymptotic mass, bighorn ewes appear to challenge older but lighter females to whom they were formerly subordinate. Although these results suggest that bighorn ewes may benefit from high social rank, we found no effect of rank on reproductive success, lamb sex ratio or lamb birth date.

Age-independent and age-dependent decreases in reproduction of females.

The terminal allocation and senescence hypotheses make opposite predictions about how age-specific reproductive effort should vary during old age. There is empirical support for both hypotheses, although reports on senescence are more numerous. Individual heterogeneity and selective mortality, however, decrease our ability to measure how reproductive effort varies during late life. The damage accumulation model proposes that terminal allocation and senescence could be partly age-independent. Using a reverse-age approach, we analysed an unusually complete record of annual reproductive success for 90 bighorn ewes that died between 7 and 18years of age. We estimated age-specific and age-independent variation of reproductive effort in late-life. Reproductive effort decreased in the two last reproductions, independently of age at death. Fecundity also decreased in the last 2years of life, with a steeper decline for older individuals. Our study reveals that reproductive senescence includes both age-dependent and age-independent components.

Heritability and genetic correlations of personality traits in a wild population of yellow-bellied marmots (Marmota flaviventris)

Describing and quantifying animal personality is now an integral part of behavioural studies because individually distinctive behaviours have ecological and evolutionary consequences. Yet, to fully understand how personality traits may respond to selection, one must understand the underlying heritability and genetic correlations between traits. Previous studies have reported a moderate degree of heritability of personality traits, but few of these studies have either been conducted in the wild or estimated the genetic correlations between personality traits. Estimating the additive genetic variance and covariance in the wild is crucial to understand the evolutionary potential of behavioural traits. Enhanced environmental variation could reduce heritability and genetic correlations, thus leading to different evolutionary predictions. We estimated the additive genetic variance and covariance of docility in the trap, sociability (mirror image stimulation), and exploration and activity in two different contexts (open‐field and mirror image simulation experiments) in a wild population of yellow‐bellied marmots (Marmota flaviventris). We estimated both heritability of behaviours and of personality traits and found nonzero additive genetic variance in these traits. We also found nonzero maternal, permanent environment and year effects. Finally, we found four phenotypic correlations between traits, and one positive genetic correlation between activity in the open‐field test and sociability. We also found permanent environment correlations between activity in both tests and docility and exploration in the MIS test. This is one of a handful of studies to adopt a quantitative genetic approach to explain variation in personality traits in the wild and, thus, provides important insights into the potential variance available for selection.

Investigating Differences in Vigilance Tactic Use within and between the Sexes in Eastern Grey Kangaroos

Aggregation is thought to enhance an animal’s security through effective predator detection and the dilution of risk. A decline in individual vigilance as group size increases is commonly reported in the literature and called the group size effect. However, to date, most of the research has only been directed toward examining whether this effect occurs at the population level. Few studies have explored the specific contributions of predator detection and risk dilution and the basis of individual differences in the use of vigilance tactics. We tested whether male and female (non-reproductive or with young) eastern grey kangaroos (Macropus giganteus) adopted different vigilance tactics when in mixed-sex groups and varied in their reliance on predator detection and/or risk dilution as group size changed. This species exhibits pronounced sexual dimorphism with females being much smaller than males, making them differentially vulnerable toward predators. We combined field observations with vigilance models describing the effects of detection and dilution on scanning rates as group size increased. We found that females with and without juveniles relied on predator detection and risk dilution, but the latter adjusted their vigilance to the proportion of females with juveniles within their group. Two models appeared to equally support the data for males suggesting that males, similarly to females, relied on predator detection and risk dilution but may also have adjusted their vigilance according to the proportion of mothers within their group. Differential vulnerability may cause sex differences in vigilance tactic use in this species. The presence of males within a group that do not, or only partially, contribute to predator detection and are less at risk may cause additional security costs to females. Our results call for reexamination of the classical view of the safety advantages of grouping to provide a more detailed functional interpretation of gregariousness.