Adaptive Maternal Effects Shape Offspring Phenotype and Survival in Natal Environments.

AbstractMaternal effects can give newborns a head start in life by adjusting natal phenotypes to natal environments, yet their strength and adaptiveness are often difficult to investigate in natural populations. Here, we studied anticipatory maternal effects and their adaptiveness in common lizards in a seminatural experimental system. Specifically, we investigated how maternal environments (i.e., vegetation cover) and maternal phenotype (i.e., activity levels and body length) can shape offspring phenotype. We further studied whether such maternal effects influenced offspring survival in natal environments varying with respect to vegetation cover, conspecific density, and, consequently, maternal fitness. More active females from dense vegetation habitats produced bigger offspring than their less active counterparts, the contrary being true for sparse vegetation habitats. Moreover, females from dense vegetation habitats produced more active offspring and more active offspring survived better in dense vegetation habitats, resulting in greater maternal fitness through maternal effects. These results suggest adaptive anticipatory maternal effects, induced by vegetation structure and mediated by activity levels that may shape early-life prospects in natal environments.

Early life parameters and personality affect oxidative status during adulthood in an altricial rodent.

It is increasingly recognized that alterations of the cellular oxidative status might be an important cost underlying challenging early life conditions. For example, an increased litter size can impose challenges as the offspring will face increased competition for maternal resources. Within a litter, individuals with relatively higher starting mass typically show higher growth rates, which can lead to increased oxidative damage. We investigated the long-term consequences of these early life parameters on the oxidative status in mature mound-building mice (Mus spicilegus). Individual differences in the animals' exploration tendency were assessed by repeated open field and novel object tests. We predicted less exploratory phenotypes, which typically show a higher stress responsiveness, to be particularly susceptible to possible effects of these early life parameters on oxidative status. We quantified oxidative damage of DNA (8-hydroxy-2'-deoxyguanosine levels, 8-OHdG) and proteins (protein carbonyl content, PCC), and activities of the antioxidants catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD) in liver and skeletal muscle tissue. 8-OHdG levels were positively associated with CAT and SOD in both tissues, indicating that increased oxidative DNA damage was associated with an upregulation of antioxidant production. Hepatic DNA damage after maturity was increased in animals from larger litters. In less exploratory animals, DNA damage and the activity of CAT and SOD in the muscle were increased, but only in individuals with higher relative starting mass (measured on postnatal day 9). This interaction may be explained by the typically higher adrenocortical activity in less exploratory phenotypes and by the higher growth in relatively heavier pups, two factors known to increase oxidative stress. These findings contribute to enlightening the complex interplay between early life conditions, personality, and oxidative status.

Individual differences in early body mass affect thermogenic performance and sibling interactions in litter huddles of the house mouse.

We asked whether within-litter differences in early body mass are associated with differences in house mouse pups' thermogenic performance and whether such variation predicts individual differences in competitive interactions for thermally more advantageous positions in the huddle. We explored pups' thermogenic performance in isolation by measuring changes in (maximal) peripheral body temperatures during a 5-min thermal challenge using infrared thermography. Changes in peripheral body temperature were significantly explained by individual differences in body mass within a litter; relatively lighter individuals showed an overall quicker temperature decrease leading to lower body temperatures toward the end of the thermal challenge compared to heavier littermates. Within the litter huddle, relatively lighter pups with a lower thermogenic performance showed consistently more rooting and climbing behavior, apparently to reach the thermally advantageous center of the huddle. This suggests that within-litter variation in starting body mass affects the pups' thermal and behavioral responses to environmental challenges.

Personality modulates proportions of CD4+ regulatory and effector T cells in response to socially induced stress in a rodent of wild origin.

The way how individuals respond to chronic challenges can vary tremendously, and such differences are closely linked to personality. The few available studies on individual differences in stress-related immunosuppression in non-human mammals have been mainly carried out with laboratory strains. We conducted a study in male mound-building mice (Mus spicilegus) of wild origin. We distinguished between high (HAN) and low anxious/neophobic (LAN) personality types, quantified by subjects' consistent and associated behavioral responses in repeated elevated plus maze and novel object tests. After reaching maturity, parts of the subjects were regularly confronted to different resident pairs over a period of 5days to provoke a condition of chronic social stress, while others were used as untreated controls. We measured fecal corticosteroid metabolite (FCM) concentrations and different cellular immune parameters from blood and spleen. Socially confronted HAN showed higher increases in FCM concentrations than LAN, indicating a more pronounced physiological stress response in the former personality type. HAN of the experimental group also showed lower percentages of effector T cells (Teff) and higher regulatory T cells (Treg) in the spleen; the latter are known for their immunosuppressive activity. Considering the ratio of Teff/Treg, animals with higher increases in FCM concentrations during the late period of the experiment showed a stronger shift towards Treg cells, supporting immunosuppressive effects of chronically elevated corticosteroid levels. Summarizing, our results strongly suggest that immunomodulatory effects of socially induced stress were altered by individual differences in anxiety/neophobia, emphasizing the significance of personality in shaping physiological responses to challenge.

Stable individual differences in separation calls during early development in cats and mice.

BACKGROUND: The development of ethologically meaningful test paradigms in young animals is an essential step in the study of the ontogeny of animal personality. Here we explore the possibility to integrate offspring separation (distress) calls into the study of consistent individual differences in behaviour in two species of mammals, the domestic cat (Felis silvestris catus) and the mound-building mouse (Mus spicilegus). Such vocal responses in young mammals are a potentially useful test option as they represent an important element of mother-offspring communication with strong implications for offspring survival. In addition, the neural control of vocalisation is closely associated with emotional state. RESULTS: We found marked similarities in the pattern of individual responses of the young of both species to separation from their mother and littermates. In the domestic cat as well as in the mound-building mouse, individual differences in the frequency of calls and to a lesser extent in locomotor activity were repeatable across age, indicating the existence of personality types. Such consistencies across age were also apparent when only considering relative individual differences among litter siblings. In both species, however, individual patterns of vocalisation and locomotor activity were unrelated. This suggests that these two forms of behavioural responses to isolation represent different domains of personality, presumably based on different underlying neurophysiological mechanisms. CONCLUSIONS: Brief separation experiments in young mammals, and particularly the measurement of separation calls, provide a promising approach to study the ontogeny of personality traits. Future long-term studies are needed to investigate the association of these traits with biologically meaningful and potentially repeatable elements of behaviour during later life.