Showing papers in "Behavior Genetics in 2005"

Cuticular Hydrocarbons: Their Evolution and Roles in Drosophila Pheromonal Communication

Abstract: I review the recent literature on cuticular hydrocarbons (CHs) in Drosophila. First, the major structural features of CHs are examined in a variety of species with regard to phylogeny. The genetic bases of the CH variation between and within species have been investigated with some of the genes involved characterized and manipulated. The effect of non-genetic factors as temperature, food and development is also examined with regard to CH production. Using a model involving the stimulating or the inhibiting role of CHs, it is possible to speculate on the mechanisms of CH perception and on the role(s) that these substances could play on sexual isolation and on the evolution of pheromonal communication.

Heritability of smoking initiation and nicotine dependence.

Abstract: In contrast to other aspects of smoking behavior, little attention has been paid to the genetics of nicotine dependence. In this paper, three models (single liability dimension, independent liability dimension and combined model) have been applied to data on smoking initiation and nicotine dependence (n = 1572 Dutch twin pairs, mean age 30.5). A combined model best described the data. This model postulates a smoking initiation dimension and a nicotine dependence dimension, which are not independent. For both males and females, individual differences in smoking initiation were explained by genetic (44%), shared environmental (51%) and unique environmental (5%) influences. The nicotine dependence dimension was influenced only by genetic (75%) and unique environmental (25%) factors. The substantial impact of genetic factors on nicotine dependence emphasizes the need for further research to localize and identify specific genes and pathways involved in nicotine dependence.

Infant rodent ultrasounds -- a gate to the understanding of sound communication.

Abstract: Components of the communication system between infant and adult rodents based on ultrasonic vocalizations (USVs) of infants are analyzed. USVs are most often emitted from a pup lost outside the nest in response to changes of: (i) body temperature, (ii) contact with adults/littermates, (iii) handling, and (iv) smell. These changes modulate the state of arousal and the emotional/motivational states and, as a result, USVs are produced. Acoustic properties of USVs seem to reflect the degrees of changes in arousal and emotion/motivation. Adult rodents are aroused by perceiving the USVs, locate the sender and show a phonotaxic approach to the sender. Acoustic properties of USVs in the frequency and time domains are described based on which adult rodents discriminate the USVs from other ultrasounds and take the USVs or adequate models of them as preferred goals of their phonotaxic approach. The preferred approach to adequate USVs is modulated by emotions/motivations, the sex of the receiver, hormonal states, experience with pups and neurotransmitter systems of the brain. The phonotaxis can be understood as the appetitive component of a pup-caring instinct. The consummatory act of the instinct is the retrieval of the lost pup. This retrieval is independent of USV presence, but it closes the communication loop activated by the emission of USVs. Communication with USVs can be used as a tool to investigate genetic and brain mechanisms of behavioral control.

Principles of rat communication: quantitative parameters of ultrasonic calls in rats.

Abstract: Ultrasonic calls used by rats during intraspecies communication have acoustic features, which can be selectively recognized by recipients, and possess a quantitative dimension reflecting the magnitude of the sender's response. This paper reviews basic principles of animal communication with particular attention to rat calls, and the features of ultrasonic calls, which could reflect such a quantitative aspect. Isolation calls of rat pups vary in frequency and duration and have changing sonographic structure over time. It is hypothesized that the quantitative "message" for the dam is encoded not only in the number of calls but also in frequency sweeps. The 22-kHz alarm calls of adults are characterized by a relatively constant sound frequency, marginal frequency modulation, and remarkable variability in call duration. It is hypothesized that quantitative aspect of these calls may be encoded in call length. Finally, the 50-kHz calls of adults, which are emitted in appetitive behavior are very short calls, with a relatively constant call duration, and a variable sound frequency. It is hypothesized that the peak frequency as well as the number of calls per time unit reflect the quantitative aspect in 50-kHz calls.

Widespread evidence for non-additive genetic variation in Cloninger's and Eysenck's personality dimensions using a twin plus sibling design.

Abstract: Studies using the classical twin design often conclude that most genetic variation underlying personality is additive in nature. However, studies analyzing only twins are very limited in their ability to detect non-additive genetic variation and are unable to detect sources of variation unique to twins, which can mask non-additive genetic variation. The current study assessed 9672 MZ and DZ twin individuals and 3241 of their siblings to investigate the environmental and genetic architecture underlying eight dimensions of personality: four from Eysenck's Personality Questionnaire and four from Cloninger's Temperament and Character Inventory. Broad-sense heritability estimates from best-fitting models were two to three times greater than the narrow-sense heritability estimates for Harm Avoidance, Novelty Seeking, Reward Dependence, Persistence, Extraversion, and Neuroticism. This genetic non-additivity could be due to dominance, additive-by-additive epistasis, or to additive genetic effects combined with higher-order epistasis. Environmental effects unique to twins were detected for both Lie and Psychoticism but accounted for little overall variation. Our results illustrate the increased sensitivity afforded by extending the classical twin design to include siblings, and may provide clues to the evolutionary origins of genetic variation underlying personality.

Genetic and Environmental Contributions to Loneliness in Adults: The Netherlands Twin Register Study

Abstract: Heritability estimates based on two small studies in children indicate that the genetic contribution to individual differences in loneliness is approximately 50%. Heritability estimates of complex traits such as loneliness may change across the lifespan, however, as the frequency, duration, and range of exposure to environmental influences accrues, or as the expression of genetic factors changes. We examined data on loneliness from 8,387 young adult and adult Dutch twins who had participated in longitudinal survey studies. A measure of loneliness was developed based on factor analyses of items of the YASR (Achenbach, (1990) The Young Adult Self Report, University of Vermont, Department of Psychiatry, Burlington, VT). Variation in loneliness was analyzed with genetic structural equation models. The estimate of genetic contributions to variation in loneliness in adults was 48%, which is similar to the heritability estimates found previously in children. There was no evidence for sex or age differences in genetic architecture. Sex differences in prevalence were significant, but we did not see an association with age or birth cohort. All resemblance between twin relatives was explained by shared genes, without any suggestion of a contribution of shared environmental factors.

Pups call, mothers rush: does maternal responsiveness affect the amount of ultrasonic vocalizations in mouse pups?

Abstract: In rats and mice, the ultrasonic vocalizations emitted by pups have been suggested to modulate maternal behavior. In the present study we show that the number of calls emitted by mouse pups can reflect maternal responsiveness. Maternal responsiveness towards pups was evaluated on postnatal day 8 using a three-compartment cage test where the mother, to reach the pups, had to cross the central part of the cage containing cues from a potentially infanticidal male. Maternal responsiveness was lower when alien rather than own pups were used as stimulus. Moreover, the administration of morphine (2.5 mg/kg, i.p.) a drug known to disrupt maternal behavior, resulted in an increase of the latency to reach the pups, as well. This behavioral and pharmacological validation supports the hypothesis that this measure can represent an index of maternal motivation. Therefore, we evaluated maternal responsiveness on day 8 postpartum and pups' ultrasound emission during isolation on day 4 and 8 of life, under conditions strongly affecting the amount of maternal behavior received by pups. C57BL/6 mothers scored higher in maternal responsiveness than BALB/c females, and their pups emitted fewer calls than BALB/c pups both on days 4 and 8. Mothers of handled pups scored higher than controls in maternal responsiveness. Handled pups showed a lower rate of calls on day 8, although they did not differ from controls on day 4. These results support our hypothesis that maternal responsiveness, that is mother promptness to respond to pups' needs, is one of the factors tuning the rate of ultrasonic emission of the offspring.

A review of the methods of studies on infant ultrasound production and maternal retrieval in small rodents.

Abstract: Ultrasonic vocalizations or calls produced by young rodents have been associated with aspects of maternal behavior, in particular retrieving. We reviewed the methods of study used by investigators on each topic, focusing on intrinsic or subject variables and extrinsic or experimental variables. Intrinsic variables included the species studied, genotypes employed, number and sex composition of the litters, and the ages of mothers and pups. Extrinsic variables for studies on ultrasonic calling included: eliciting stimuli, test surroundings, and the length of observation. Extrinsic variables in studies of maternal retrieval included the testing procedure and the length of observation. The methods used in studies within each topic vary greatly. In an effort to facilitate progress in the areas, especially with respect to isolating individual genes with a contribution to ultrasonic call production or studying the effects of pharmaceutical agents on either behavior, we propose some standardization of nomenclature and/or procedure in four areas: (1) the stimuli or situations used to elicit ultrasonic calls, (2) the length of observation in ultrasonic call studies, (3) the number of pups per litter and the sex composition of litters in both ultrasonic call and maternal retrieval studies and finally, (4) the apparatus or testing situation used in studies of pup retrieval.

The longitudinal relationship between processing speed and cognitive ability: genetic and environmental influences.

Abstract: Goals of the present study were to investigate the relationship between age changes in speed and cognition and the genetic and environmental influences on that relationship. Latent growth models and quantitative genetic methods were applied to data from the Swedish Adoption/Twin Study of Aging. The sample included 778 individuals from both complete and incomplete twin pairs who participated in at least 1 of 4 testing occasions over a 13-year-period. Four factors were constructed from 11 cognitive measures: verbal, spatial, memory, and processing speed. Results indicate that for measures of fluid abilities, the explanatory value of processing speed is paramount for both mean cognitive performance and acceleration with age. A significant proportion of the genetic influences on cognitive ability arose from genetic factors affecting processing speed. For measures of fluid abilities, it is not the linear age changes but the accelerating age changes in cognition that share genetic variance with processing speed.

Assessing reliability, heritability and general cognitive ability in a battery of cognitive tasks for laboratory mice.

Abstract: This report includes the first sibling study of mouse behavior, and presents evidence for a heritable general cognitive ability (g) factor influencing cognitive batteries. Data from a population of male and female outbred mice (n = 84), and a replication study of male sibling pairs (n = 167) are reported. Arenas employed were the T-maze, the Morris water maze, the puzzle box, the Hebb-Williams maze, object exploration, a water plus-maze, and a second food-puzzle arena. The results show a factor structure consistent with the presence of g in mice. Employing one score per arena, this factor accounts for 41% of the variance in the first study (or 36% after sex regression) and 23% in the second, where this factor also showed sibling correlations of 0.17-0.21, which translates into an upper-limit heritability estimate of around 40%. Reliabilities of many tasks are low and consequently set an even lower ceiling for inter-arena or sibling correlations. Nevertheless, the factor structure is seen to remain fairly robust across permutations of the battery composition and the current findings fit well with other recent studies.

Breeding for 50-kHz positive affective vocalization in rats.

Abstract: Adolescent and adult rats exhibit at least two distinct ultrasonic vocalizations that reflect distinct emotional states. Rats exhibit 22-kHz calls during social defeat, drug withdrawal, as well as in anticipation of aversive events. In contrast, 50-kHz calls are exhibited in high rates during play behavior, mating, as well as in anticipation of rewarding events. The neurochemistry of 22-kHz and 50-kHz calls closely matches that of negative and positive emotional systems in humans, respectively. The aim of this study was to replicate and further evaluate selective breeding for 50-kHz vocalization, in preparation for the analysis of the genetic underpinnings of the 50-kHz ultrasonic vocalization (USV). Isolate housed adolescent rats (23–26 days old) received experimenter administered tactile stimulation (dubbed “tickling”), which mimicked the rat rough-and-tumble play behavior. This stimulation has previously been shown to elicit high levels of 50-kHz USVs and to be highly rewarding in isolate-housed animals. Each tickling session consisted of 4 cycles of 15 seconds stimulation followed by 15 seconds no stimulation for a total of 2 min, and was repeated once per day across 4 successive days. Rats were then selected for either High or Low levels of sonographically verified 50-kHz USVs in response to the stimulation, and a randomly selected line served as a control (Random group). Animals emitted both 22-kHz and 50-kHz types of calls. After 5 generations, animals in the High Line exhibited significantly more 50-kHz and fewer 22-kHz USVs than animals in the Low Line. Animals selected for low levels of 50-kHz calls showed marginally more 22-kHz USVs then randomly selected animals but did not differ in the rate of 50-kHz calls. These results extend our previous findings that laboratory rats could be bred for differential rates of sonographically verified 50-kHz USVs.

Family dysfunction interacts with genes in the causation of antisocial symptoms.

Abstract: There is emerging evidence of gene-environment interaction effects on conduct problems, both from adoption studies and from a study using a measured genotype. An association between non-violent family dysfunction and conduct problems has also been reported, although not in the context of gene-environment interaction studies. The aim of this study was to examine the interaction of genes and family dysfunction in contributing to conduct problems in young people. Parents of 278 monozygotic and 378 dizygotic twin pairs, aged 5-18, from the CaStANET birth cohort twin register were questioned about zygosity, conduct problems and family environment. Using structural equation modeling we tested for main and interactive effects of genes and family dysfunction modelled as an environmental "moderator variable". Both main and gene-environment interaction effects were highly significant. It was concluded that a risk genotype conferring susceptibility to family dysfunction is responsible for most of the variance in antisocial symptoms in childhood and adolescence.

Opposite Effects of Androgen Receptor CAG Repeat Length on Increased Risk of Left-Handedness in Males and Females

Abstract: Prenatal exposure to testosterone has been hypothesised to effect lateralization by influencing cell death in the foetal brain. Testosterone binds to the X chromosome linked androgen receptor, which contains a polymorphic polyglutamine CAG repeat, the length of which is positively correlated with testosterone levels in males, and negatively correlated in females. To determine whether the length of the androgen receptor mediates the effects of testosterone on laterality, we examined the association between the number of CAG repeats in the androgen receptor gene and handedness for writing. Association was tested by adding regression terms for the length of the androgen receptor alleles to a multi-factorial-threshold model of liability to left-handedness. In females we found the risk of left-handedness was greater in those with a greater number of repeats (p=0.04), this finding was replicated in a second independent sample of female twins (p=0.014). The length of the androgen receptor explained 6% of the total variance and 24% of the genetic variance in females. In males the risk of left-handedness was greater in those with fewer repeats (p=0.02), with variation in receptor length explaining 10% of the total variance and 24% of the genetic variance. Thus, consistent with Witelson's theory of testosterone action, in all three samples the likelihood of left handedness increased in those individuals with variants of the androgen receptor associated with lower testosterone levels.

Selective breeding for an infant phenotype: rat pup ultrasonic vocalization (USV).

Abstract: To examine processes underlying generational and developmental influences on anxiety, this laboratory produced two lines of (N:NIH strain) rats, selectively bred on the basis extreme rates of ultrasonic vocalization in 2 minutes of isolation at Postnatal Day 10. The research reviewed in this article focuses on: (1) establishment of the selectively bred lines; (2) defining infant behavioral and physiological phenotypes and (3) determining whether infantile USV phenotypes endure over development. The High and Low lines have diverged widely in their USV rates from each other and from the Random control line, which has maintained N:NIH strain rates overall from generation to generation. Beginning in the 11th generation, High USV pups have shown significantly higher frequencies of defecation and urination during isolation screening than the Low USV and random control line. Both lines show altered autonomic regulation of heart rates (HR) in response to stressors as juveniles and adults. These differences in HR responses in High and Low lines appear to be mediated by changes in the balance of sympathetic versus parasympathetic mechanisms. Other behavioral characteristics of the High line are consistent with an "anxious"/ "depressive" phenotype, such as vocalizations to touch in a novel environment, and performance in the Porsolt Swim, whereas Low line shows few differences in anxiety behavior. Future work will resolve the similarities and differences in the High and Low phenotypes and provide a developmental perspective to the growing body of information about affective regulation in humans and animals provided by selectively bred animal models.

Contributions of genes and environments to stability and change in externalizing and internalizing problems during elementary and middle school.

Abstract: We examined longitudinally collected behavioral reports by teachers on a unique twin sample at the ages of 7, 8, 9, 10, 11, and 12 years. As twin and adoption studies implicate the role of genetic influence on behavioral problems found to be stable in epidemiological samples, the current study employs a developmental behavior genetic model to examine the extent to which genetic and environmental contributions to problem behaviors are stable and/or change during development. In this sample of 410 monozygotic (MZ) and 354 dizygotic (DZ) twins, MZ twins were rated as more similar than DZ twins on average. In general, boys were more frequently rated as displaying externalizing behaviors than were girls across each of the six observations, while girls' internalizing problems were found not to be significantly different from boys'. For both sexes, stability in externalizing problem behaviors was due to a single common genetic factor whose effects acted pleiotropically at each age in the presence of unique environmental influences that were transmitted from age-to-age. Change was largely due to uncorrelated age-specific non-shared environmental and additive genetic effects. Contributions to stability for internalizing problems were due to age-to-age transmission of earlier expressed genetic effects. Change for girls and boys internalizing problems were largely due to environmental experiences unique to siblings along with uncorrelated age-specific genetic effects. These results further inform the notion that individual environments are important factors in the etiology of problem behaviors, but suggest that heritable contributions to phenotypic stability are largely the same across middle childhood and early adolescence. Clinical implications of these findings are discussed.

Heritability of word recognition in middle-aged men varies as a function of parental education.

Abstract: Although it is of lifelong importance, reading ability is studied primarily in children and adolescents. We examined variation in word recognition in 347 middle-aged male twin pairs. Overall heritability (a2) was 0.45, and shared environmental influences (c2) were 0.28. However, parental education moderated heritability such that a2 was 0.21 at the lowest parental education level and 0.69 at the highest level; c2 was 0.52 and 0.00, respectively. This constitutes a parental education × environment interaction. The higher heritability was due to a decrease in the magnitude of shared environmental factors, rather than an increase in the magnitude of genetic factors. Other cognitive studies have reported gene × environment interactions, but patterns may differ as a function of age or specific cognitive abilities. Our results suggest that shared environmental factors in families with low parental education have long-lasting effects on word recognition ability, well beyond any critical period for developing reading proficiency.

Genetic effects on physical health: Lower at higher income levels.

Abstract: Given the robust finding that people in higher income groups tend to experience better physical health, there is interest in identifying mechanisms underlying this gradient. Using a nationwide sample of 719 twin pairs from the National Survey of Midlife Development in the United States, we investigated the possibility that gene-environment interaction underlies the income-health gradient. We observed that genetic variance associated with 2 measures of physical health, number of chronic illnesses and body mass index, each declined significantly with increasing income. This interaction effect could not be removed by adjusting income for the presence of health insurance coverage and education, suggesting that the interaction is not simply a result of differences in levels of those characteristics with income.

The genetic basis of academic achievement on the Queensland Core Skills Test and its shared genetic variance with IQ.

Abstract: First, this study examined genetic and environmental sources of variation in performance on a standardised test of academic achievement, the Queensland Core Skills Test (QCST) (Queensland Studies Authority, 2003a) Second, it assessed the genetic correlation among the QCST score and Verbal and Performance IQ measures using the Multidimensional Aptitude Battery (MAB), [Jackson, D N (1984) Multidimensional Aptitude Battery manual Port Huron, MI:Research Psychologist Press, Inc] Participants were 256 monozygotic twin pairs and 326 dizygotic twin pairs aged from 15 to 18 years (mean 17 years ± 04 [SD]) when achievement tested, and from 15 to 22 years (mean 16 years ± 04 [SD]) when IQ tested Univariate analysis indicated a heritability for the QCST of 072 Adjustment to this estimate due to truncate selection (downward adjustment) and positive phenotypic assortative mating (upward adjustment) suggested a heritability of 076 The phenotypic (081) and genetic (091) correlations between the QCST and Verbal IQ (VIQ) were significantly stronger than the phenotypic (057) and genetic (064) correlations between the QCST and Performance IQ (PIQ) The findings suggest that individual variation in QCST performance is largely due to genetic factors and that common environmental effects may be substantially accounted for by phenotypic assortative mating Covariance between academic achievement on the QCST and psychometric IQ (particularly VIQ) is to a large extent due to common genetic influences

Mixed-Effects Variance Components Models for Biometric Family Analyses

Abstract: Recent substantive research on biometric analyses of twin and family data has used both a biometric path analysis model (PAM) and a biometric variance components model (VCM). Methodological research on these same topics have suggested benefits of using linear structural equation model algorithms (SEMA) as well as mixed effect multilevel algorithms (MEMA). To better understand the potential similarities and differences among these approaches we first highlight the algebraic equivalence between the standard biometric PAM and the corresponding biometric VCM models for family data. Second, we demonstrate how several SEMA programs based on either the PAM or VCM approach produce equivalent estimates for all phenotypic and biometric parameters. Third, we show how the biometric VCM approach (but not the PAM approach) can be easily programmed using current MEMA programs (e.g., SAS PROC MIXED). We then expand the scope of these different approaches to include measured covariates, observed variable interactions and multiple relatives within each family. MEMA software is compared to SEMA software for programming complex models, including the flexibility of data input, treatment of missing data, inclusion of covariates, and ease of accommodating varying numbers of observations (per family or individual).

Continuity and change in preschool ADHD symptoms: longitudinal genetic analysis with contrast effects.

Abstract: The genetic and environmental mediation of continuity and change in parent-reported ADHD symptoms were investigated in a cohort of over 6000 twin pairs at 2, 3 and 4 years of age. Genetic analyses of the cross-sectional data yielded heritability estimates of 0.78–0.81 at each age, with contrast effects. A common pathway model provided the best fit to the longitudinal data, indicating that genetic influences underlie 91% of the stable variance in ADHD symptomatology. In other words, what is stable for ADHD symptoms is largely genetic. Contrast effects acting in the same direction at different ages contributed to the observed continuity:longitudinal correlations were greater for dizygotic than monozygotic twins.

Experimental Manipulation of Sexual Selection and the Evolution of Courtship Song in Drosophila pseudoobscura

Abstract: Courtship song serves as a sexual signal and may contribute to reproductive isolation between closely related species. Using lines of Drosophila pseudoobscura experimentally selected under different sexual selection regimes, we tested whether increased promiscuity and enforced monogamy led to evolutionary changes in courtship song elements. In D. pseudoobscura, males produce both a low and high rate repetition song. We found that both song types diverged after selection and that the direction of changes was consistent with ordered hypotheses of predicted directions of change under the different mating system structures. In particular, latency to the initiation of song and duration of the interpulse interval (IPI) decreased in highly promiscuous lines and increased in monogamous lines. These results suggest that courtship song may rapidly evolve under different mating system structures, representing either functional evolution of more stimulatory song under conditions of strong sexual selection, or might result from increased courtship vigor, or represent correlated evolution. Some speciation theory predicts that increased sexual selection should result in increased variance of traits between allopatric populations, facilitating reproductive isolation. We also found that courtship song elements were not equally variable between replicate lines.

Mutations and natural genetic variation in the courtship song of Drosophila.

Abstract: All Drosophila species have a courtship repertoire by which a male stimulates a female to mate with him. In many species, males vibrate their wings to produce courtship song, an element of courtship that plays an important role in female choice. Each species has a unique courtship song, with the major differences among species songs being in timing and/or structure. Analysis of genetic mutations has revealed 17 genes that affect courtship song in Drosophila melanogaster. Most of the genes were first identified as affecting another trait and were subsequently shown to affect song. Quantitative genetic studies have demonstrated a polygenetic additive genetic architecture for many song traits. Few candidate genes, identified through the classical genetic approach, coincide with the regions implicated as affecting natural variation. With many new tools in genetic analysis and the multiple Drosophila genome projects currently underway, the ability to relate mutational and quantitative analyses will improve.

Reformulating and simplifying the DF analysis model.

Abstract: DeFries-Fulker (DF) Analysis for unselected populations is reformulated as a no-intercept model with centered variables and only two independent variables. The reformulation serves three purposes. First, the original formulation implicitly estimated two different values for c2 and two values for h2. The new formulation resolves this ambiguity. Second, because the original formulation estimated h2 with the coefficient from a regression-interaction term, whether to center the interaction variables was unclear. The new formulation explicitly resolves this issue. Finally, the new formulation estimates fewer parameters, and therefore improves estimation efficiency and statistical power.

Personality and coping: a study of twins reared apart and twins reared together.

Abstract: The relative importance of genetic and environmental factors for stress coping styles, age and gender differences, and the relationship between coping styles and personality traits were assessed in middle-aged and older adult twins reared apart and reared together, as part of the ongoing Swedish Adoption/Twin Study of Aging (SATSA). The Billings and Moos Coping Measure was administered to 1339 individual twins (in 446 intact pairs). The mean age was 58.0 ± 12.8. Moderate genetic influences and significant gender differences in variance estimates were found for the three coping scales (Problem Solving, Turning to Others, and Avoidance). Turning to Others and Avoidance in women also showed shared rearing environmental influences. In contrast, no age differences in variance estimates were found in this sample. Multivariate model fitting indicated that genetic influences on adults’ coping differentially reflect genetic factors in common with personality traits. The sources of covariation also showed significant gender differences.

The role of male courtship song in species recognition in Drosophila montana.

Abstract: In many Drosophila species the male courtship song is an essential part of a successful courtship, playing a role in species-recognition and/or in sexual selection exercised by the females on conspecific males. In Drosophila montana, specific traits of the courtship song (the length and the carrier frequency of sound pulses) have earlier been shown to play an important role in intraspecific mate choice. Here we show that the male song (especially the interpulse interval) also plays a role in species-recognition, maintaining sexual isolation between sympatric species. We succeeded in breaking down sexual isolation between D. montana females and D. lummei males by playing the females simulated courtship song with a species-specific interpulse interval while they were courted by a mute (wingless) male. Involvement of different song traits in intra- and interspecific mate choice suggests that the song may be affected by both directional and stabilizing selection.

Environmental mediation and the twin design.

Abstract: Behavior genetic twin designs are increasingly used to study the effects of a measured environment whilst controlling for genetic variation. In this research note, we show that, in the context of the classical twin design, (1) when the environmental variable is necessarily shared between twins, the notion of controlling for genetic influence is logically flawed and (2) when the environmental variable varies between twins in the same family, partial control for genetic influence is possible, but only if appropriate analytic models are used, which is commonly not the case. Based on a simple simulation study, recommendations are given as to which methods should be applied and which should be avoided.

Examination of the effect of the polymorphic CGG repeat in the FMR1 gene on cognitive performance.

Abstract: A CGG repeat sequence located in the 5′ untranslated region of the FMR1 gene is polymorphic with respect to size and stability of the repeat during parent-offspring transmission. When expanded to over 200 repeats, the gene is hypermethylated and silenced, leading to fragile X syndrome (FXS). Recently, alleles with large unmethylated repeat tracts (premutations) have been associated with ovarian failure and a late-onset tremor/ataxia syndrome, symptoms unrelated to FXS. To further investigate the phenotype consequence of high repeat alleles, we have analyzed Wechsler adult intelligence scales-III (WAIS-III) measures on 66 males and 217 females with a wide range of repeat sizes. Among females only, we found that FMR1 repeat size and transcript level significantly explained approximately 4% of the variance in the Verbal IQ summary measure, suggesting that this polymorphism is one of many factors that influence variation in cognitive performance. Because of the well established association of increasing repeat size with decreasing age at menopause, we also investigated the reproductive stage and use of hormone replacement therapy (HRT) as a covariate to model verbal intelligence quotient (VIQ). We found that it explained an additional 5% of the variance in VIQ, but did not interact with FMR1 repeat and transcript level.

Sexual selection and speciation in hawaiian Drosophila.

Abstract: Many ideas about sexual selection and speciation have been stimulated by considering Hawaiian Drosophila. In turn, the ideas and models have stimulated research with the flies, particularly members of the planitibia group. This paper describes high points of some of the models and reviews data that are relevant to understanding sexual selection and speciation in this species group.

Genetic covariation between event-related potential (ERP) and behavioral non-ERP measures of working-memory, processing speed, and IQ

Abstract: The aim of this study was to identify genetic covariants for fundamental measures of brain function (event-related potentials (ERPs): P300 latency and slow wave amplitude recorded in a working-memory task) and more complex cognitive measures (behavioral non-ERP measures: working-memory performance, information processing speed, IQ). Data were collected from 252 monozygotic and 297 dizygotic twin pairs aged 16. Multivariate modeling identified two independent genetic factors associated with processing speed that also influenced working-memory performance (one reflected the duration of neural activity required to evaluate target information, the other reflected more general cognitive and speed-related abilities). However, the allocation of neural resources, as assessed by ERP slow wave amplitude measures, was not associated with the other cognitive measures investigated. Thus, of the ERP measures examined, P300 latency, but not slow wave amplitude, may be an informative measure to include (i.e., with working-memory performance) in future multivariate linkage and association analyses of cognitive function.

Distinct influences of neonatal epidermal growth factor challenge on adult neurobehavioral traits in four mouse strains.

Abstract: Epidermal growth factor (EGF) receptor (ErbB1) signals regulate dopaminergic development and function and are implicated in schizophrenia. We evaluated genetic effects on neurobehavioral changes induced by neonatal EGF administration, using four mouse strains. Subcutaneous EGF administration increased phosphorylation of brain ErbB1 in all strains, although DBA/2 and C57BL/6 mice had lower basal phosphorylation. Neonatal EGF treatment differentially influenced physical and behavioral/cognitive development, depending on mouse strain. Prepulse inhibition was decreased in DBA/2 and C57BL/6 mice but not C3H/He and ddY mice. Locomotor activity was accelerated in DBA/2 mice, but reduced in ddY mice. EGF treatment enhanced fear-learning performance with a tone cue in DBA/2 mice, but decreased performance with tone and context cues in C3H/He and ddY mice, respectively. The strain-dependent behavioral sensitivity was correlated with basal ErbB1 phosphorylation. Genetic components regulating brain ErbB1 signaling strongly influence the direction and strength of behavioral responses stemming from the neonatal neurotrophic perturbation.