Several personality traits are mainly expressed in a social context, and others, which are not restricted to a social context, can be affected by the social interactions with conspecifics. In this paper, we focus on the recently proposed hypothesis that social niche specialization (i.e. individuals in a population occupy different social roles) can explain the maintenance of individual differences in personality. We first present ecological and social niche specialization hypotheses. In particular, we show how niche specialization can be quantified and highlight the link between personality differences and social niche specialization. We then review some ecological factors (e.g. competition and environmental heterogeneity) and the social mechanisms (e.g. frequency-dependent, state-dependent and social awareness) that may be associated with the evolution of social niche specialization and personality differences. Finally, we present a conceptual model and methods to quantify the contribution of ecological factors and social mechanisms to the dynamics between personality and social roles. In doing so, we suggest a series of research objectives to help empirical advances in this research area. Throughout this paper, we highlight empirical studies of social niche specialization in mammals, where available.

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The Klebsiella group, found in humans, livestock, plants, soil, water and wild animals, is genetically and ecologically diverse. Many species are opportunistic pathogens and can harbour diverse classes of antimicrobial resistance genes. Healthcare-associated Klebsiella pneumoniae clones that are non-susceptible to carbapenems can spread rapidly, representing a high public health burden. Here we report an analysis of 3,482 genome sequences representing 15 Klebsiella species sampled over a 17-month period from a wide range of clinical, community, animal and environmental settings in and around the Italian city of Pavia. Northern Italy is a hotspot for hospital-acquired carbapenem non-susceptible Klebsiella and thus a pertinent setting to examine the overlap between isolates in clinical and non-clinical settings. We found no genotypic or phenotypic evidence for non-susceptibility to carbapenems outside the clinical environment. Although we noted occasional transmission between clinical and non-clinical settings, our data point to a limited role of animal and environmental reservoirs in the human acquisition of Klebsiella spp. We also provide a detailed genus-wide view of genomic diversity and population structure, including the identification of new groups.

Mesenchymal stem cells (MSC) are known to be a valuable cell source for tissue engineering and regenerative medicine. However, one of the main limiting steps in their clinical use is the amplification step. MSC expansion on microcarriers has emerged during the last few years, fulfilling the lack of classical T-flasks expansion. Even if the therapeutic potential of MSC as aggregates has been recently highlighted, cell aggregation during expansion has to be avoided. Thus, MSC culture on microcarriers has still to be improved, notably concerning cell aggregation prevention. The aim of this study was to limit cell aggregation during MSC expansion on Cytodex-1®, by evaluating the impact of several culture parameters. First, MSC cultures were performed at different agitation rates (0, 25, and 75 rpm) and different initial cell densities (25 and 50×10(6) cell g(-1) Cytodex-1®). Then, the MSC aggregates were put into contact with additional available surfaces (T-flask, fresh and used Cytodex-1®) at different times (before and after cell aggregation). The results showed that cell aggregation was partly induced by agitation and prevented in static cultures. Moreover, cell aggregation was dependent on cell density and correlated with a decrease in the total cell number. It was however shown that the aggregated organization could be dissociated when in contact with additional surfaces such as T-flasks or fresh Cytodex-1® carriers. Finally, cell aggregation could be successfully limited in spinner flask by adding fresh Cytodex-1® carriers before its onset. Those results indicated that MSC expansion on agitated Cytodex-1® microcarriers could be performed without cell aggregation, avoiding a decrease in total cell number.

SUMMARYVariation in how individuals cope behaviourally and physiologically with stressors is widespread and can have a significant impact on life-history traits and fitness. Individual coping styles are characterised by differential behavioural and adrenocortical reactivity to various challenges. As stress hormones can affect the production of reactive chemical species and the antioxidant status, individuals with different coping styles may differ also in oxidative status. Field studies on wild mammalian populations are few in number and none so far has simultaneously tested the relationship between coping style, adrenocortical reactivity and oxidative status in the same individuals. We measured individual variation in coping styles along a proactive-reactive continuum together with variation in baseline and stress-induced plasma oxidative damage, plasma non-enzymatic antioxidant capacity and cortisol in wild alpine marmots, Marmota marmota. Confirmatory path analysis revealed that different coping styles are accompanied by different baseline and stress-induced plasma oxidative statuses. Our findings also highlight the potential role of cortisol as a mediator of such differences.Key words: coping style, personality, oxidative stress, cortisol, open-field test, mammals. THE JOURNAL OF EXPERIMENTAL BIOLOGY 375Oxidative stress and coping styles and physical activities in socio-sexual contexts, which are known to differ among coping styles [e.g. mice Mus musculus (Koolhaas et al., 1999) and great tits Parus major (Carere et al., 2001; Both et al., 2005;Groothuis and Carere, 2005)], could significantly affect the biomarkers of oxidative status and thus expose individuals to oxidative challenges of different magnitudes (e.g. Alessio, 1993;Costantini et al., 2008b). Oxidative stress results from an imbalance between the production of reactive chemical species and antioxidant defences, in favour of the former with a consequent increase in the rate of generation of oxidative damage (Sies, 1991;Halliwell and Gutteridge, 2007;Costantini and Verhulst, 2009). Oxidative stress may also be defined as a disruption of redox signaling and control (Jones, 2006), which regulate the redox balance and the antioxidant response to oxidative insults.The importance of oxidative stress as one component affecting the progression of diseases, ageing and health span (sensu Salmon et al., 2010) has been recognised for decades (Harman, 1956; Beckman and Ames, 1998;Halliwell and Gutteridge, 2007). However, only recently has it been recognised that oxidative stress may also represent an important modulator of trade-offs between life-history traits in wild populations (Costantini, 2008;Dowling and Simmons, 2009;Monaghan et al., 2009;. Recent studies have also suggested that differences in oxidative stress physiology may be associated with behavioural differences. In mice selected for different levels of aggression, Costantini et al. (Costantini et al., 2008b) found higher baseline non-enzymatic antioxidant capacity in less aggressive mice. In t...