Issues in the genetics of social behavior: revisited

INTERACTING PHENOTYPES AND THE EVOLUTIONARY PROCESS: I. DIRECT AND INDIRECT GENETIC EFFECTS OF SOCIAL INTERACTIONS

Interacting phenotypes are traits whose expression is affected by interactions with conspecifics. Commonly-studied interacting phenotypes include aggression, courtship, and communication. More extreme examples of interacting phenotypes-traits that exist exclusively as a product of interactions-include social dominance, intraspecific competitive ability, and mating systems. We adopt a quantitative genetic approach to assess genetic influences on interacting phenotypes. We partition genetic and environmental effects so that traits in conspecifics that influence the expression of interacting phenotypes are a component of the environment. When the trait having the effect is heritable, the environmental influence arising from the interaction has a genetic basis and can be incorporated as an indirect genetic effect. However, because it has a genetic basis, this environmental component can evolve. Therefore, to consider the evolution of interacting phenotypes we simultaneously consider changes in the direct genetic contributions to a trait (as a standard quantitative genetic approach would evaluate) as well as changes in the environmental (indirect genetic) contribution to the phenotype. We then explore the ramifications of this model of inheritance on the evolution of interacting phenotypes. The relative rate of evolution in interacting phenotypes can be quite different from that predicted by a standard quantitative genetic analysis. Phenotypic evolution is greatly enhanced or inhibited depending on the nature of the direct and indirect genetic effects. Further, unlike most models of phenotypic evolution, a lack of variation in direct genetic effects does not preclude evolution if there is genetic variance in the indirect genetic contributions. The available empirical evidence regarding the evolution of behavior expressed in interactions, although limited, supports the predictions of our model.

Implementation of the mouse frailty index

Frailty is considered a state of high vulnerability for adverse health outcomes for people of the same age. Those who are frail have higher mortality, worse health outcomes, and use more health care services than those who are not frail. Despite this, little is known about the biology of frailty, the effect of frailty on pharmacological or surgical outcomes, and potential interventions to attenuate frailty. In humans, frailty can be quantified using a frailty index (FI) based on the principle of deficit accumulation. The recent development of an FI in naturally ageing mice provides an opportunity to conduct frailty research in a validated preclinical model. The mouse FI has been successfully used across a wide range of applications; however, there are some factors that should be considered in implementing this tool. This review summarises the current literature, presents some original data, and suggests areas for future research on the current applications of the mouse FI, inter-rater reliability of the FI, the effect of observer characteristics and environmental factors on mouse FI scores, and the individual items that make up the FI assessment. The implementation of this tool into preclinical frailty research should greatly accelerate translational research in this important field.

Aggression in non-human vertebrates: Genetic mechanisms and molecular pathways

Aggression is an adaptive behavioral trait that is important for the establishment of social hierarchies and competition for mating partners, food, and territories. While a certain level of aggression can be beneficial for the survival of an individual or species, abnormal aggression levels can be detrimental. Abnormal aggression is commonly found in human patients with psychiatric disorders. The predisposition to aggression is influenced by a combination of environmental and genetic factors and a large number of genes have been associated with aggression in both human and animal studies. In this review, we compare and contrast aggression studies in zebrafish and mouse. We present gene ontology and pathway analyses of genes linked to aggression and discuss the molecular pathways that underpin agonistic behavior in these species. © 2015 Wiley Periodicals, Inc.

The transcriptomic and evolutionary signature of social interactions regulating honey bee caste development

The caste fate of developing female honey bee larvae is strictly socially regulated by adult nurse workers. As a result of this social regulation, nurse-expressed genes as well as larval-expressed genes may affect caste expression and evolution. We used a novel transcriptomic approach to identify genes with putative direct and indirect effects on honey bee caste development, and we subsequently studied the relative rates of molecular evolution at these caste-associated genes. We experimentally induced the production of new queens by removing the current colony queen, and we used RNA sequencing to study the gene expression profiles of both developing larvae and their caregiving nurses before and after queen removal. By comparing the gene expression profiles of queen-destined versus worker-destined larvae as well as nurses observed feeding these two types of larvae, we identified larval and nurse genes associated with caste development. Of 950 differentially expressed genes associated with caste, 82% were expressed in larvae with putative direct effects on larval caste, and 18% were expressed in nurses with putative indirect effects on caste. Estimated selection coefficients suggest that both nurse and larval genes putatively associated with caste are rapidly evolving, especially those genes associated with worker development. Altogether, our results suggest that indirect effect genes play important roles in both the expression and evolution of socially influenced traits such as caste.

Indirect genetic effects and the evolution of aggression in a vertebrate system

Aggressive behaviours are necessarily expressed in a social context, such that individuals may be influenced by the phenotypes, and potentially the genotypes, of their social partners. Consequently, it has been hypothesized that indirect genetic effects (IGEs) arising from the social environment will provide a major source of heritable variation on which selection can act. However, there has been little empirical scrutiny of this to date. Here we test this hypothesis in an experimental population of deer mice (Peromyscus maniculatus). Using quantitative genetic models of five aggression traits, we find repeatable and heritable differences in agonistic behaviours of focal individuals when presented with an opponent mouse. For three of the traits, there is also support for the presence of IGEs, and estimated correlations between direct and indirect genetic (rAO,F) effects were high. As a consequence, any selection for aggression in the focal individuals should cause evolution of the social environment as a correlated response. In two traits, strong positive rAO,F will cause the rapid evolution of aggression, while in a third case changes in the phenotypic mean will be constrained by negative covariance between direct and IGEs. Our results illustrate how classical analyses may miss important components of heritable variation, and show that a full understanding of evolutionary dynamics requires explicit consideration of the genetic component of the social environment.

Issues in the search for candidate genes in mice as potential animal models of human aggression

Conceptual and methodological issues in the search for candidate genes for mouse aggression and for the development of animal models of human aggression are considered. First, the focus is on genetic and then behavioural aspects of the search for candidate genes in mice. For the genetic aspect, two approaches are presented. In mice, these are chromosome mapping of polymorphic genes and evaluation of gene (polymorphic or monomorphic) function using knockout mutants. For the behavioural aspect, several parameters, including the type of aggression, measure of aggression, test situation and opponent type can have effects on the obtained genetics. This is illustrated for the offence type of attack behaviour in mice. The current combination of sophisticated genetic and behavioural analyses will result in time in the identification of many of the genes with effects on variation and development of one or more types of murine aggression. Since mouse and humans have many homologous genes mapped to homologous chromosome regions, it is conceivable that individual genes identified for one or more types of mouse aggression may be developed as animal models for human aggression. Genetic, physiological and behavioural limitations and uses of such models are discussed.

Ontogenetic interaction between social relationships and defensive burying behavior in the rat

The present experiments clarify sexual and social relationship factors related to the development of defensive burying behavior in rats. Rats were raised in isolation, or in a variety of pairs differing in sex, age or familiarity during the juvenile and post-juvenile period. In Experiment 1, decreased burying behavior was found in both male and female rats during the juvenile stage when they were reared in isolation, or with an adult female, or for males reared with a same-age female. In Experiment 2, female rats isolated during the juvenile stage who were reared after the juvenile stage with a same-sex, non-isolated rat, showed as much burying behavior as rats reared with a littermate; this was not found for male rats. When both male and female rats isolated during the juvenile stage were reared with each other after isolation, they maintained reduced burying behavior in adulthood. These sex differences in the effect of different social groupings are likely due to the differences in social relationships during the juvenile and after puberty, when social dominance relationships emerge in male rats. In Experiment 3, the effects of social dominance relationships on burying behavior were investigated in male rats. Subordination increased the freezing tendency as a passive defense, while social tension accompanied with rearing with an adult male produced decreased burying behavior as a proactive defense. These findings suggest that affiliative relationships involving playful contacts activate and maintain burying behavior, but familiarity is not a significant factor, while dominance relationships modulate the patterns of burying behavior.

A mouse model system for genetic analysis of sociability: C57BL/6J versus BALB/cJ inbred mouse strains

BACKGROUND

Impairments in social behaviors are highly disabling symptoms of autism, schizophrenia, and other psychiatric disorders. Mouse model systems are useful for identifying the many genes and environmental factors likely to affect complex behaviors, such as sociability (the tendency to seek social interaction). To progress toward developing such a model system, we tested the hypothesis that C57BL/6J inbred mice show higher levels of sociability than BALB/cJ inbred mice.

METHODS

Mice tested for sociability were 4- and 9-week-old, male and female C57BL/6J and BALB/cJ mice. On 2 consecutive days, the sociability of each test mouse toward an unfamiliar 4-week-old DBA/2J stimulus mouse was assessed with a social choice paradigm conducted in a three-chambered apparatus. Measures of sociability included the time that the test mouse spent near versus far from the stimulus mouse, the time spent directly sniffing the stimulus mouse, and the time spent in contact between test and stimulus mice in a free interaction.

RESULTS

C57BL/6J mice showed higher levels of sociability than BALB/cJ mice overall in each of these measures.

CONCLUSIONS

We propose that C57BL/6J and BALB/cJ mice will be a useful mouse model system for future genetic and neurobiological studies of sociability.

Modulation of affect after chronic exposure to the anabolic steroid 17alpha-methyltestosterone in adult mice

A battery of behavioral tasks in C57BL/6J mice was used to assess changes in affective components of behavior after systemic exposure to the anabolic-androgenic steroid (AAS) 17alpha-methyltestosterone (7.5 mg/kg). Gonadal weight in both sexes was reduced after 16 days of AAS exposure. Changes in discrete components of social behaviors were observed. No changes were recorded in the elevated plus-maze, the light-dark transition, and defensive behavior tests on exposure to 17alpha-methyltestosterone. When compared with controls, AAS-exposed females received a greater number of shocks, and AAS-exposed males displayed a shorter recovery time to consume water after a negative reinforcer in the modified Vogel conflict test. Results show that systemic exposure to a single AAS modified social behaviors, whereas minimal effects on anxiety-related behaviors were observed according to sex.

Automated apparatus for quantitation of social approach behaviors in mice

Mouse models of social dysfunction, designed to investigate the complex genetics of social behaviors, require an objective methodology for scoring social interactions relevant to human disease symptoms. Here we describe an automated, three chambered apparatus designed to monitor social interaction in the mouse. Time spent in each chamber and the number of entries are scored automatically by a system detecting photocell beam breaks. When tested with the automated equipment, juvenile male C57BL/6J mice spent more time in a chamber containing a stranger mouse than in an empty chamber (sociability), similar to results obtained by the observer scored method. In addition, automated scoring detected a preference to spend more time with an unfamiliar stranger than a more familiar conspecific (preference for social novelty), similar to results obtained by the observer scored method. Sniffing directed at the wire cage containing the stranger mouse correlated significantly with time spent in that chamber, indicating that duration in a chamber represents true social approach behavior. Number of entries between chambers did not correlate with duration of time spent in the chambers; entries instead proved a useful control measure of general activity. The most significant social approach behavior took place in the first five minutes of both the sociability and preference for social novelty tests. Application of these methods to C57BL/6J, DBA/2J and FVB/NJ adult males revealed that all three strains displayed tendencies for sociability and preference for social novelty. To evaluate the importance of the strain of the stranger mouse on sociability and preference for social novelty, C57BL/6J subject mice were tested either with A/J strangers or with C57BL/6J strangers. Sociability and preference for social novelty were similar with both stranger strains. The automated equipment provides an accurate and objective approach to measuring social tendencies in mice. Its use may allow higher-throughput scoring of mouse social behaviors in mouse models of social dysfunction.

Social approach-avoidance behavior of inbred mouse strains towards DBA/2 mice

Little is known about the genetics of social approach-avoidance behaviors. We measured social approach-avoidance of prepubescent female C57BL/6J, DBA/2J, FVB/NJ, AKR/J, A/J, and BALB/cJ mice towards prepubescent DBA/2J female mice. C57BL/6J mice showed the greatest predominance of approach, while BALB/cJ mice showed the greatest predominance of avoidance. Thus, this phenotype is affected by spontaneous genetic variation in mice and can be measured in an assay useful for future neurogenetic studies.

Expanded characterization of the social interaction abnormalities in mice lacking Dvl1

Dvl1 is one of three murine Dishevelled genes widely expressed in embryonic development and in the adult central nervous system. Dishevelled proteins are a necessary component of the Wnt and planar cell polarity developmental signaling pathways. We reported previously that mice deficient in Dvl1 exhibited abnormal social interaction and sensorimotor gating. To assess the validity of our earlier findings, we replicated the previous behavioral tests and included several new assays. The behaviors assessed included: social interaction, sensorimotor reflexes, motor activity, nociception, prepulse inhibition of acoustic startle (PPI) and learning and memory. Assessments with an explicit social component included: social dominance test, whisker trimming, nest building, home-cage huddling and ultrasonic vocalization rate analysis in pups. In addition, separate cohorts of wildtype and Dvl1-null mice were assessed for social recognition of a conspecific. Replicating the original report, Dvl1-null mice were impaired in several tasks containing an explicit social component. However, no impairment was observed in the social memory task. A previously observed deficit in PPI did not replicate in two institutions. In conclusion, we provide evidence that the social interaction phenotype of Dvl1-deficient mice has a strong genetic influence, but the sensorimotor gating deficit was subject to environmental influences. The specificity of observed social interaction deficits also suggests that lack of Dvl1 is associated with deficits in the recognition of social hierarchy and dominance.

Individual differences in response to a stranger: social impulsivity as a dimension of temperament in vervet monkeys (Cercopithecus aethiops sabaeus)

Social impulsivity in response to a stranger was assessed in male vervet monkeys (Cercopithecus aethiops sabaeus) using the Intruder Challenge Test. Vervets (N = 128, ages 3-18 years) were presented with an unfamiliar adult male at the periphery of the home enclosure. An index of impulsivity reflecting variation in the tendency to rapidly approach, engage, and challenge the intruder was derived from factor analysis of behavioral responses. Scale reliability (alpha = .84) and test-retest consistency (intraclass correlation = .83) were high, indicating that this index reliably and efficiently measures a stable aspect of temperament from impulsive to inhibited. Impulsivity scores peaked at age 4, when vervet males typically emigrate from the natal group. The highest ranking males in each group were more likely to score in the moderate range, whereas lower ranking males were more likely to score in the highest (impulsive) or lowest (inhibited) quartiles.

Social interaction and sensorimotor gating abnormalities in mice lacking Dvl1

Mice completely deficient for Dvl1, one of three mouse homologs of the Drosophila segment polarity gene Dishevelled, were created by gene targeting. Dvl1-deficient mice are viable, fertile, and structurally normal. Surprisingly, these mice exhibited reduced social interaction, including differences in whisker trimming, deficits in nest-building, less huddling contact during home cage sleeping, and subordinate responses in a social dominance test. Sensorimotor gating was abnormal, as measured by deficits in prepulse inhibition of acoustic and tactile startle. Thus, Dvl1 mutants may provide a model for aspects of several human psychiatric disorders. These results are consistent with an interpretation that common genetic mechanisms underlie abnormal social behavior and sensorimotor gating deficits and implicate Dvl1 in processes underlying complex behaviors.

A proposed test battery and constellations of specific behavioral paradigms to investigate the behavioral phenotypes of transgenic and knockout mice

Behavioral phenotyping of transgenic and knockout mice requires rigorous, formal analyses. Well-characterized paradigms can be chosen from the established behavioral neuroscience literature. This review describes (1) a series of neurological and neuropsychological tests which are effectively used as a first screen for behavioral abnormalities in mutant mice, and (2) a series of specific behavioral paradigms, clustered by category. Included are multiple paradigms for each category, including learning and memory, feeding, analgesia, aggression, anxiety, depression, schizophrenia, and drug abuse models. Examples are given from the experiences of the authors, in applying these experimental designs to transgenic and knockout mice. Extensive references for each behavioral paradigm are provided, to allow new investigators to access the relevant literature on behavioral methodology.