Maintenance Of Individual Differences Research Articles

Individual differences are consistent across changes in mating status and mediated by biogenic amines

Although aspects of an individual’s state are well-known to influence the expression of behavior, it is still unclear how elements of state affect consistent among-individual differences in behavior. With binary, irreversible elements of state, such as mating status, there may be optimal behavioral phenotypes before and after mating, with individuals often prioritizing mate acquisition before and resource acquisition after. Yet, limited plasticity may prevent optimal behavior in both contexts. Additionally, it remains largely unknown if some consistencies in neural or physiological traits may limit the ability of the organism to respond to state changes. In this study, we investigated how changes in a binary state variable, mating status, affected both the mean expression and among-individual variation in behavior and web structure of the redback spider, Latrodectus hasselti. Furthermore, we explored the role of biogenic amines in potentially mediating individual differences in behavior and web structure. We found that mated females were overall more aggressive than virgin females and also built webs structured primarily for capturing prey rather than safety. We also found that individual differences in behavior and web structure were maintained across mating statuses, which indicates the stability of these traits and may drive personality-specific state-dependent fitness trade-offs. Finally, we found that aggressive spiders had higher central nervous system dopamine levels. Interestingly, web structure was often correlated with a catabolite of tyramine (N-acetyltyramine), suggesting that variation in amine catabolism, and not the concentrations of the amines themselves, may drive individual differences in some traits. Our results demonstrate that although individuals show plasticity in response to changes in state, specifically mating status, individuals also maintain among-individual differences across this state change. Thus, aggressive individuals before mating will tend to be aggressive after. This maintenance of individual differences across state may drive differential fitness benefits before and after mating for different behavioral phenotypes. Furthermore, we show that biogenic amines and their catabolites are related to individual differences, thus identifying a potential mechanism underlying consistent variation.

An experimental test of density-dependent selection on temperament traits of activity, boldness and sociability.

Temperament traits are seen in many animal species, and recent evolutionary models predict that they could be maintained by heterogeneous selection. We tested this prediction by examining density-dependent selection in juvenile common lizards Zootoca vivipara scored for activity, boldness and sociability at birth and at the age of 1 year. We measured three key life-history traits (juvenile survival, body growth rate and reproduction) and quantified selection in experimental populations at five density levels ranging from low to high values. We observed consistent individual differences for all behaviours on the short term, but only for activity and one boldness measure across the first year of life. At low density, growth selection favoured more sociable lizards, whereas viability selection favoured less active individuals. A significant negative correlational selection on activity and boldness existed for body growth rate irrespective of density. Thus, behavioural traits were characterized by limited ontogenic consistency, and natural selection was heterogeneous between density treatments and fitness traits. This confirms that density-dependent selection plays an important role in the maintenance of individual differences in exploration-activity and sociability.

Social environment influences the relationship between genotype and gene expression in wild baboons

Variation in the social environment can have profound effects on survival and reproduction in wild social mammals. However, we know little about the degree to which these effects are influenced by genetic differences among individuals, and conversely, the degree to which social environmental variation mediates genetic reaction norms. To better understand these relationships, we investigated the potential for dominance rank, social connectedness and group size to modify the effects of genetic variation on gene expression in the wild baboons of the Amboseli basin. We found evidence for a number of gene-environment interactions (GEIs) associated with variation in the social environment, encompassing social environments experienced in adulthood as well as persistent effects of early life social environment. Social connectedness, maternal dominance rank and group size all interacted with genotype to influence gene expression in at least one sex, and either in early life or in adulthood. These results suggest that social and behavioural variation, akin to other factors such as age and sex, can impact the genotype-phenotype relationship. We conclude that GEIs mediated by the social environment are important in the evolution and maintenance of individual differences in wild social mammals, including individual differences in responses to social stressors.

Heritability and Fitness Correlates of Personality in the Ache, a Natural-Fertility Population in Paraguay

The current study assessed the heritability of personality in a traditional natural-fertility population, the Ache of eastern Paraguay. Self-reports (n = 110) and other-reports (n = 66) on the commonly used Big Five Personality Inventory (i.e., extraversion, agreeableness, conscientiousness, neuroticism, openness) were collected. Self-reports did not support the Five Factor Model developed with Western samples, and did not correlate with other-reports for three of the five measured personality factors. Heritability was assessed using factors that were consistent across self- and other-reports and factors assessed using other-reports that showed reliabilities similar to those found in Western samples. Analyses of these items in combination with a multi-generation pedigree (n = 2,132) revealed heritability estimates similar to those found in most Western samples, although we were not able to separately estimate the influence of the common environment on these traits. We also assessed relations between personality and reproductive success (RS), allowing for a test of several mechanisms that might be maintaining heritable variation in personality. Phenotypic analyses, based largely on other-reports, revealed that extraverted men had higher RS than other men, but no other dimensions of personality predicted RS in either sex. Mothers with more agreeable children had more children, and parents mated assortatively on personality. Of the evolutionary processes proposed to maintain variation in personality, assortative mating, selective neutrality, and temporal variation in selection pressures received the most support. However, the current study does not rule out other processes affecting the evolution and maintenance of individual differences in human personality.

Stability and instability of childhood traits: Implications for personality development of animals

Concepts of animal personality and human temperament are nearly identical, both emphasizing overt behaviors rather than conscious processes, and assuming a primary role of biology in shaping individual differences. A point of divergence is emphasis on development among temperament scholars. Whereas most definitions of personality and temperament emphasize differential continuity-the maintenance of individual differences in behavioral tendencies over time-several behaviors demonstrate absolute discontinuity-age-related changes in mean levels. Attention to species-wide changes in behaviors may generate insight regarding the forces that govern individual differences. Differential continuity may also be heterotypic, with an inferred genotypic attribute being manifest in different behaviors at different ages. Structural continuity-persistence of correlational patterns among variables at different ages-represents a tool for identifying coherence in the common underpinnings of these diverse behaviors. This article describes research exemplifying these forms of continuity in humans, and suggests potential implications for animal personality investigations.

The maintenance of individual differences in the sensitivity of acute and neuropathic pain behaviors to electroacupuncture in rats

“Responder” Sprague–Dawley (SD) rats that were sensitive to electroacupuncture (EA) in an acute thermal pain test (i.e. tail flick latency [TFL] test) maintained sensitivity to EA in the warm allodynia test after peripheral nerve injury. Similarly, the “non-responder” SD rats that were insensitive to EA in the TFL test were also insensitive to EA in the allodynia test. The EA-induced analgesic effects in the TFL test were significantly higher in CCK-A receptor deficient, Otsuka Long-Evans Tokushima Fatty (OLETF) rats than in their littermates, Long-Evans Tokushima Otsuka (LETO) rats. Similarly, the anti-allodynic effects of EA were significantly greater in OLETF rats than in LETO rats. These results suggest that the individual differences in the sensitivity of acute pain behavior to EA were maintained in neuropathic pain behavior following peripheral nerve injury, and that CCK-A receptor expression plays an important role in mediating this phenomenon.

Role of the adrenal gland in early post-hatching differentiation of alternative male phenotypes in the tree lezard ( Urosaurus ornatus)

During development, sex steroids are important in establishing differences between males and females. However, sex steroids also are involved in the development and maintenance of individual differences in morphology and behavior within each sex. As adults, male tree lizards ( Urosaurus ornatus) exhibit alternative reproductive tactics correlated with dewlap (throat fan) coloration. Males with orange-blue dewlaps are aggressive and territorial, whereas males with orange dewlaps are less aggressive and employ a satellite strategy. Dewlap coloration develops within the first 90 days after hatching and remains fixed throughout life. Recent work demonstrates that individual males differ in progesterone and testosterone secretion during development, suggesting that these hormones regulate the development of alternative male phenotypes. The current work uses in vitro incubation of adrenal and gonadal tissues to identify the source of progesterone and testosterone during the period of male differentiation and to follow ontogenetic changes in hormone release. The results indicate that, in all developmental stages sampled, adrenal incubations primarily contain progesterone and corticosterone whereas gonadal incubations contain primarily testosterone. These data indicate that the hatchling adrenal is the primary source of progesterone during early post-hatching development. Since progesterone has been demonstrated to play a role in the establishment of individual differences in morphology and behavior in male tree lizards, our results suggest that the hatchling adrenal gland plays an important role in post-hatching development of alternative male phenotypes.