Does the Fraternal Birth Order Effect Influence Handedness?

The fraternal birth order effect (FBOE) is the phenomenon whereby the probability that a man has a same-sex sexual orientation in adulthood increases with each biological older brother. Several studies have found evidence that the FBOE is limited to right-handed men, and left-handed men do not show an FBOE. Recent debates about the appropriate methods for quantifying the FBOE center on distinguishing the FBOE from other effects, such as the female fecundity effect (FFE), whereby mothers more prone to bearing gay sons are also more fecund. The FBOE and FFE are confounded in that a real FFE will result in data consistent with the FBOE under some analyses. Here, we applied some recent proposed analytic methods for the FBOE to the property of handedness. A straightforward application of Khovanova's technique to the binary trait of handedness yielded support for a fraternal birth order effect consistent with the maternal immune hypothesis, in that the ratios of handedness differed between men with one older brother only, and men with one younger brother only, while no such effect was seen in women. This effect was not seen, however, when the confounding effects of parental age were controlled for. Models including factors to simultaneously test multiple posited effects find significant female fecundity effects, as well as paternal age and birth order effects on handedness in men, but no FBOE. The effects seen in women were different, with no fecundity or parental age effects, but birth order and sex of older siblings had effects. We conclude, based on this evidence, that many of the factors thought to contribute to sexual orientation in men may also have an influence on handedness, and further note that parental age is a potential confound which may be overlooked by some analyses of the FBOE.

Zebrafish (Danio rerio) shoaling in light and dark conditions involves a complex interplay between vision and lateral line.

We know little about how - or even if in some species - fish shoal in darkness. We hypothesized that 'dark shoaling' occurs in zebrafish and therefore must depend upon lateral line sensory input. Shoaling in groups of five adult zebrafish was analyzed with motion tracking software. We measured average inter-individual distance, time near the arena wall (thigmotaxis zone) and total distance traveled under normal room light, and in near-complete darkness (infrared light at 850 nm). These observations were repeated in fish treated with cobalt chloride (CoCl2), which ablates lateral line function. In untreated controls, dark shoaling was reduced compared to in light, but nonetheless still present. Elimination of lateral line sensory input by CoCl2 treatment similarly reduced, but did not eliminate, shoaling under both light and dark. Our findings indicate that normal zebrafish shoaling in light or dark requires both visual and lateral line inputs, with neither alone sufficient for normal shoaling.

Epigenetic Regulation and Environmental Sex Determination in Cichlid Fishes.

Studying environmental sex determination (ESD) in cichlids provides a phylogenetic and comparative approach to understand the evolution of the underlying mechanisms, their impact on the evolution of the overlying systems, and the neuroethology of life history strategies. Natural selection normally favors parents who invest equally in the development of male and female offspring, but evolution may favor deviations from this 50:50 ratio when environmental conditions produce an advantage for doing so. Many species of cichlids demonstrate ESD in response to water chemistry (temperature, pH, and oxygen concentration). The relative strengths of and the exact interactions between these factors vary between congeners, demonstrating genetic variation in sensitivity. The presence of sizable proportions of the less common sex towards the environmental extremes in most species strongly suggests the presence of some genetic sex-determining loci acting in parallel with the ESD factors. Sex determination and differentiation in these species does not seem to result in the organization of a final and irreversible sexual fate, so much as a life-long ongoing battle between competing male- and female-determining genetic and hormonal networks governed by epigenetic factors. We discuss what is and is not known about the epigenetic mechanism behind the differentiation of both gonads and sex differences in the brain. Beyond the well-studied tilapia species, the 2 best-studied dwarf cichlid systems showing ESD are the South American genus Apistogramma and the West African genus Pelvicachromis. Both species demonstrate male morphs with alternative reproductive tactics. We discuss the further neuroethology opportunities such systems provide to the study of epigenetics of alternative life history strategies and other behavioral variation.

SHANK3 Genotype Mediates Speech and Language Phenotypes in a Nonclinical Population.

Mutations affecting the synaptic-scaffold gene SHANK3 represent the most common genetic causes of autism with intellectual disability, accounting for about 1-2% of cases. Rare variants of this gene have also been associated with schizophrenia, and its deletion results in the autistic condition known as Phelan-McDermid syndrome. Despite the importance of SHANK3 as a paradigmatic gene mediating neurodevelopmental disorders, its psychological effects in nonclinical populations have yet to be studied. We genotyped the nonsynonymous, functional SHANK3 SNP rs9616915 in a large population of typical individuals scored for autism spectrum traits (the Autism Quotient, AQ) and schizotypy spectrum traits (the Schizotypal Personality Questionnaire, SPQ-BR). Males, but not females, showed significant genotypic effects for the SPQ-BR subscale associated with speech and language: Odd Speech. These findings, in conjunction with animal model studies showing vocalization and auditory effects of SHANK3 mutations, and studies indicating severe language alterations and speech-associated white matter tract abnormalities in Phelan-McDermid syndrome, suggest that SHANK3 differentially affects the development and expression of human language and speech. Imaging genetic and speech-language studies of typical individuals carrying different genotypes of rs9616915 should provide novel insights into the neurological and psychological bases of speech and language alterations among individuals with SHANK3 mutations and Phelan-McDermid syndrome.

Cognitive Empathy as Imagination: Evidence From Reading the Mind in the Eyes in Autism and Schizotypy.

How is cognitive empathy related to sociality, imagination, and other psychological constructs? How is it altered in disorders of human social cognition? We leveraged a large data set (1,168 students, 62% female) on the Reading the Mind in the Eyes test (RMET), the Autism Quotient (AQ), and the Schizotypal Personality Questionnaire (SPQ-BR) to test the hypotheses that the RMET, as a metric of cognitive empathy, reflects mainly social abilities, imagination, or both. RMET showed the expected female bias in performance, though only for eyes that expressed emotions and not for neutral expressions. RMET performance was significantly, and more strongly, associated with the AQ and SPQ subscales that reflect aspects of imagination (AQ-Imagination and SPQ-Magical Ideation) than aspects of social abilities (AQ-Social, AQ-Communication, and SPQ-Interpersonal subscales). These results were confirmed with multiple regression analysis, which also implicated increased attention (AQ-Attention Switching and, marginally non-significantly, AQ-Attention to Detail) in RMET performance. The two imagination-related correlates of RMET performance also show the strongest sex biases for the AQ and SPQ: male biased in AQ-Imagination, and female biased in SPQ-Magical Ideation, with small to medium effect sizes. Taken together, these findings suggest that cognitive empathy, as quantified by the RMET, centrally involves imagination, which is underdeveloped (with a male bias) on the autism spectrum and overdeveloped (with a female bias) on the schizotypy spectrum, with optimal emotion-recognition performance intermediate between the two. The results, in conjunction with previous studies, implicate a combination of optimal imagination and focused attention in enhanced RMET performance.

Epigenetic regulation of gonadal and brain aromatase expression in a cichlid fish with environmental sex determination.

A fit animal must develop testes or ovaries, with brain and physiology to match. In species with alternative male morphs this coordination of development across tissues operates within sexes as well as between. For Pelvicachromis pulcher, an African cichlid in which early pH exposure influences both sex and alternative male morph, we sequence both copies of aromatase (cyp19a1), a key gene for sex determination. We analyze gene expression and epigenetic state, comparing gonad and brain tissue from females, alternative male morphs, and fry. Relative to brain, we find elevated expression of the A-copy in the ovaries but not testes. Methylation analysis suggests strong epigenetic regulation, with one region specifying sex and another specifying tissue. We find elevated brain expression of the B-copy with no sex or male morph differences. B-copy methylation follows that of the A-copy rather than corresponding to B-copy expression. In 30-day old fry, we see elevated B-copy expression in the head, but we do not see the expected elevated A-copy expression in the trunk that would reflect ovarian development. Interestingly, the A-copy epialleles that distinguish ovaries from testes are among the most explanatory patterns for variation among fry, suggesting epigenetic marking of sex prior to differentiation and thus laying the groundwork for mechanistic studies of epigenetic regulation of sex and morph differentiation.

AMBRA1, Autophagy, and the Extreme Male Brain Theory of Autism.

The extreme male brain theory of autism posits that its male bias is mediated by exaggeration of male-biased sex differences in the expression of autism-associated traits found in typical populations. The theory is supported by extensive phenotypic evidence, but no genes have yet been described with properties that fit its predictions. The autophagy-associated gene AMBRA1 represents one of the top genome-wide "hits" in recent GWAS studies of schizophrenia, shows sex-differential expression, and has been linked with autism risk and traits in humans and mice, especially or exclusively among females. We genotyped the AMBRA1 autism-risk SNP in a population of typical humans who were scored for the dimensional expression of autistic and schizotypal traits. Females, but not males, homozygous for the GG genotype showed a significant increase in score for the single trait, the Autism Quotient-Imagination subscale, that exhibits a strong, significant male bias in typical populations. As such, females with this genotype resembled males for this highly sexually dimorphic, autism-associated phenotype. These findings support the extreme male brain hypothesis and indicate that sex-specific genetic effects can mediate aspects of risk for autism.

The submerged plus maze as an assay for studying anxiety-like behaviour in fish.

The elevated plus maze is a commonly used and well-validated test of anxiety-related behaviour in rodents. The use of fish in behavioural neuroscience paradigms is increasing, necessitating an equivalent test for studying anxiety-like behaviour in fish. Because behaviour in the elevated plus maze is driven by aversion to open space, the submerged plus maze described here uses transparent walls to elicit similar behaviour in fish. The tendency of fish to explore or avoid the sections of the maze containing transparent walls is used as proxy for anxiety level. This submerged plus maze was designed and validated for convict cichlid (Amatitlania nigrofasciata) fish.

Spirituality, dimensional autism, and schizotypal traits: The search for meaning.

The relationships of spirituality with human social cognition, as exemplified in autism spectrum and schizophrenia spectrum cognitive variation, remain largely unstudied. We quantified non-clinical levels of autism spectrum and schizotypal spectrum traits (using the Autism Quotient and the Schizotypal Personality Questionnaire-Brief Revised) and dimensions of spirituality (using the Hardt Spirituality Questionnaire) in a large sample of undergraduate students. We tested in particular the hypothesis, based on the diametrical model of autism and psychosis, that autism should be negatively associated, and positive schizotypal traits should be positively associated, with spirituality. Our primary findings were threefold. First, in support of the diametric model, total Spirituality score was significantly negatively correlated with total Autism Quotient score, and significantly positively correlated with Positive Schizotypal traits (the Schizotypal Personality Cognitive-Perceptual subscale), as predicted. Second, these associations were driven mainly by opposite patterns regarding the Search for Meaning Spirituality subscale, which was the only subscale that was significantly negatively associated with autism, and significantly positively associated with Positive Schizotypal traits. Third, Belief in God was positively correlated with Positive Schizotypal traits, but was uncorrelated with autism traits. The opposite findings for Search for Meaning can be interpreted in the contexts of well-supported cognitive models for understanding autism in terms of weak central coherence, and understanding Positive Schizotypal traits in terms of enhanced salience.

Submerged plus maze: A novel test for studying anxiety-like behaviour in fish.

The elevated plus maze is a prominent and well-documented test for studying anxiety in rodents. Fish are becoming more prevalent in studies of anxiety, yet the elevated plus maze has not been adapted and validated for fish. In the present study, we created an aquatic version of the elevated plus maze called the 'submerged plus maze,' which is shaped like a plus symbol with four arms alternating between black and transparent walls. We used convict cichlid fish (Amatitlania nigrofasciata) and administered diazepam to validate the apparatus for studying anxiety-like behaviour. After diazepam exposure, fish spent more time in and entered more open arms than after vehicle exposure, consistent with the effect of benzodiazepines on rodents in the elevated plus maze. The submerged plus maze maintains construct validity for testing anxiety in convict cichlid fish.

Segregating polymorphism in the NMDA receptor gene GRIN2A, schizotypy, and mental rotation among healthy individuals.

Common alleles associated with psychiatric disorders are often regarded as deleterious genes that influence vulnerability to disease, but they may also be considered as mediators of variation in adaptively structured cognitive phenotypes among healthy individuals. The schizophrenia-associated gene GRIN2A (glutamate ionotropic receptor NMDA type subunit 2a) codes for a protein subunit of the NMDA (N-methyl-D-aspartate) receptor that underlies central aspects of human cognition. Pharmacological NMDA blockage recapitulates the major features of schizophrenia in human subjects, and represents a key model for the neurological basis of this disorder. We genotyped two functional GRIN2A polymorphisms in a large population of healthy individuals who were scored for schizotypy and mental imagery/manipulation (the mental rotation test). Rare-allele homozygosity of the promoter microsatellite rs3219790 was associated with high total schizotypy (after adjustment for multiple comparisons) and with enhanced mental rotation ability (nominally, but not after adjustment for multiple comparisons), among males. These findings provide preliminary evidence regarding a genetic basis to previous reports of enhanced mental imagery in schizophrenia and schizotypy. The results also suggest that some schizophrenia-related alleles may be subject to cognitive tradeoffs involving both positive and negative effects on psychological phenotypes, which may help to explain the maintenance of psychiatric-disorder risk alleles in human populations.

Modulation of complex spike activity differs between zebrin-positive and -negative Purkinje cells in the pigeon cerebellum.

The cerebellum is organized into parasagittal zones defined by its climbing and mossy fiber inputs, efferent projections, and Purkinje cell (PC) response properties. Additionally, parasagittal stripes can be visualized with molecular markers, such as heterogeneous expression of the isoenzyme zebrin II (ZII), where sagittal stripes of high ZII expression (ZII+) are interdigitated with stripes of low ZII expression (ZII-). In the pigeon vestibulocerebellum, a ZII+/- stripe pair represents a functional unit, insofar as both ZII+ and ZII- PCs within a stripe pair respond best to the same pattern of optic flow. In the present study, we attempted to determine whether there were any differences in the responses between ZII+ and ZII- PCs within a functional unit in response to optic flow stimuli. In pigeons of either sex, we recorded complex spike activity (CSA) from PCs in response to optic flow, marked recording sites with a fluorescent tracer, and determined the ZII identity of recorded PCs by immunohistochemistry. We found that CSA of ZII+ PCs showed a greater depth of modulation in response to the preferred optic flow pattern compared with ZII- PCs. We suggest that these differences in the depth of modulation to optic flow stimuli are due to differences in the connectivity of ZII+ and ZII- PCs within a functional unit. Specifically, ZII+ PCs project to areas of the vestibular nuclei that provide inhibitory feedback to the inferior olive, whereas ZII- PCs do not. NEW & NOTEWORTHY Although the cerebellum appears to be a uniform structure, Purkinje cells (PCs) are heterogeneous and can be categorized on the basis of the expression of molecular markers. These phenotypes are conserved across species, but the significance is undetermined. PCs in the vestibulocerebellum encode optic flow resulting from self-motion, and those that express the molecular marker zebrin II (ZII+) exhibit more sensitivity to optic flow than those that do not express zebrin II (ZII-).

Topographic Organization of Inferior Olive Projections to the Zebrin II Stripes in the Pigeon Cerebellar Uvula.

This study was aimed at mapping the organization of the projections from the inferior olive (IO) to the ventral uvula in pigeons. The uvula is part of the vestibulocerebellum (VbC), which is involved in the processing of optic flow resulting from self-motion. As in other areas of the cerebellum, the uvula is organized into sagittal zones, which is apparent with respect to afferent inputs, the projection patterns of Purkinje cell (PC) efferents, the response properties of PCs and the expression of molecular markers such as zebrin II (ZII). ZII is heterogeneously expressed such that there are sagittal stripes of PCs with high ZII expression (ZII+), alternating with sagittal stripes of PCs with little to no ZII expression (ZII-). We have previously demonstrated that a ZII+/- stripe pair in the uvula constitutes a functional unit, insofar as the complex spike activity (CSA) of all PCs within a ZII+/- stripe pair respond to the same type of optic flow stimuli. In the present study we sought to map the climbing fiber (CF) inputs from the IO to the ZII+ and ZII- stripes in the uvula. We injected fluorescent Cholera Toxin B (CTB) of different colors (red and green) into ZII+ and ZII- bands of functional stripe pair. Injections in the ZII+ and ZII- bands resulted in retrograde labeling of spatially separate, but adjacent regions in the IO. Thus, although a ZII+/- stripe pair represents a functional unit in the pigeon uvula, CF inputs to the ZII+ and ZII- stripes of a unit arise from separate regions of the IO.

A genetic locus for paranoia.

The psychological effects of brain-expressed imprinted genes in humans are virtually unknown. Prader-Willi syndrome (PWS) is a neurogenetic condition mediated by genomic imprinting, which involves high rates of psychosis characterized by hallucinations and paranoia, as well as autism. Altered expression of two brain-expressed imprinted genes, MAGEL2 and NDN, mediates a suite of PWS-related phenotypes, including behaviour, in mice. We phenotyped a large population of typical individuals for schizophrenia-spectrum and autism-spectrum traits, and genotyped them for the single-nucleotide polymorphism rs850807, which is putatively functional and linked with MAGEL2 and NDN Genetic variation in rs850807 was strongly and exclusively associated with the ideas of reference subscale of the schizophrenia spectrum, which is best typified as paranoia. These findings provide a single-locus genetic model for analysing the neurological and psychological bases of paranoid thinking, and implicate imprinted genes, and genomic conflicts, in human mentalistic thought.

The SETDB2 locus: evidence for a genetic link between handedness and atopic disease.

The gene SETDB2, which mediates aspects of laterality in animal model systems, has recently been linked with human handedness as measured continuously on a scale from strong left to strong right. By contrast, it was marginally associated with a left-right dichotomous measure, and it showed no evidence of association with absolute handedness strength independent of direction. We genotyped the SETDB2 handedness-associated single nucleotide polymorphism, rs4942830, in a large healthy population likewise phenotyped for continuous, absolute, and dichotomous handedness variables. Our results demonstrated significant effects of rs4942830 genotype on continuous handedness, and weaker, marginal effects on dichotomous handedness, but no effects on absolute handedness. These results help to establish the locus marked by the SNP rs4942830 as a strong candidate for mediating human handedness. Intriguingly, rs4942830 is also in complete linkage disequilibrium with rs386770867, a polymorphism recently shown to affect human serum levels of IgE production and other atopic phenotypes. These findings implicate this locus in the longstanding links of handedness with asthma and other atopic diseases.

Segregating polymorphisms of FOXP2 are associated with measures of inner speech, speech fluency and strength of handedness in a healthy population.

We genotyped a healthy population for three haplotype-tagging FOXP2 SNPs, and tested for associations of these SNPs with strength of handedness and questionnaire-based metrics of inner speech characteristics (ISP) and speech fluency (FLU), as derived from the Schizotypal Personality Questionnaire-BR. Levels of mixed-handedness were positively correlated with ISP and FLU, supporting prior work on these two domains. Genotype for rs7799109, a SNP previously linked with lateralization of left frontal regions underlying language, was associated with degree of mixed handedness and with scores for ISP and FLU phenotypes. Genotype of rs1456031, which has previously been linked with auditory hallucinations, was also associated with ISP phenotypes. These results provide evidence that FOXP2 SNPs influence aspects of human inner speech and fluency that are related to lateralized phenotypes, and suggest that the evolution of human language, as mediated by the adaptive evolution of FOXP2, involved features of inner speech.

Inferior olivary projection to the zebrin II stripes in lobule IXcd of the pigeon flocculus: A retrograde tracing study.

Zebrin II (ZII; a.k.a. aldolase C) is expressed heterogeneously in Purkinje cells (PCs) such that there are sagittal stripes of high expression (ZII+) interdigitated with stripes of little or no expression (ZII-). The pigeon flocculus receives visual-optokinetic information and is important for generating compensatory eye movements. It consists of 4 sagittal zones based on PC complex spike activity (CSA) in response to rotational optokinetic stimuli. There are two zones where CSA responds best to rotation about the vertical axis (VA), interdigitated with two zones where CSA responds best to rotation about an horizontal axis (HA). These optokinetic zones relate to the ZII stripes in folium IXcd of the flocculus, such that an optokinetic zone spans a ZII+/- pair: the HA zones span the P5+/- and P7+/- ZII stripe pairs, whereas the VA zones correspond to ZII stripe pairs P4+/- and P6+/-. In the present study, we used fluorescent retrograde tracing to determine the olivary inputs to the ZII+ and ZII- stripes within the functional pairs. We found that separate but adjacent areas of the medial column of the inferior olive (mcIO) project to the ZII+ and ZII- stripes within each of the functional pairs. Thus, although a ZII+/- stripe pair represents a functional unit in the pigeon flocculus insofar as the CSA of all PCs in the stripe pair encodes similar sensory information, the olivary inputs to the ZII+ and ZII- stripes arise from different, although adjacent, regions of the mcIO.

Isotocin neuronal phenotypes differ among social systems in cichlid fishes.

Social living has evolved numerous times across a diverse array of animal taxa. An open question is how the transition to a social lifestyle has shaped, and been shaped by, the underlying neurohormonal machinery of social behaviour. The nonapeptide neurohormones, implicated in the regulation of social behaviours, are prime candidates for the neuroendocrine substrates of social evolution. Here, we examined the brains of eight cichlid fish species with divergent social systems, comparing the number and size of preoptic neurons that express the nonapeptides isotocin and vasotocin. While controlling for the influence of phylogeny and body size, we found that the highly social cooperatively breeding species (n = 4) had fewer parvocellular isotocin neurons than the less social independently breeding species (n = 4), suggesting that the evolutionary transition to group living and cooperative breeding was associated with a reduction in the number of these neurons. In a complementary analysis, we found that the size and number of isotocin neurons significantly differentiated the cooperatively breeding from the independently breeding species. Our results suggest that isotocin is related to sociality in cichlids and may provide a mechanistic substrate for the evolution of sociality.

Are there consistent behavioral differences between sexes and male color morphs in Pelvicachromis pulcher?

Adult sex ratios in the kribensis cichlid (Pelvicachromis pulcher) are influenced by environmental conditions during early development. These environmental sex-determining factors may also organize life-long variation in social behavior within each sex. If this is true, then individual differences in behavior may be, at least in part, expressions of the relative strength of sexual differentiation of that individual. As adults, kribensis males take on one of four alternative color morphs. Males of the yellow morph tend toward breeding monogamously and are produced at higher frequency under female-biasing environmental conditions, while males of the red morph tend more towards breeding polygynously and are produced more frequently by male-biasing early environments. Here we test whether these two alternative kribensis male color morphs show consistent behavioral differences as predicted by an underlying behavioral syndrome of relative feminization to masculinization. We compare these males to females in five different behavioral tests: an aggression assay, an open field exploration task, a novel environment emergence task, and three cerebral lateralization tests. We hypothesize that red males will show more exaggerated sex differences across all behaviors. We find that red males are hypermasculinized as predicted with respect to aggressive behavior and activity levels, but not all behaviors follow this pattern. We find no evidence for a common behavioral syndrome underlying personality traits across females, yellow males and red males.