A computational neuroimaging study of reinforcement learning and goal-directed exploration in schizophrenia spectrum disorders.

BACKGROUND: Prior evidence indicates that negative symptom severity and cognitive deficits, in people with schizophrenia (PSZ), relate to measures of reward-seeking and loss-avoidance behavior (implicating the ventral striatum/VS), as well as uncertainty-driven exploration (reliant on rostrolateral prefrontal cortex/rlPFC). While neural correlates of reward-seeking and loss-avoidance have been examined in PSZ, neural correlates of uncertainty-driven exploration have not. Understanding neural correlates of uncertainty-driven exploration is an important next step that could reveal insights to how this mechanism of cognitive and negative symptoms manifest at a neural level. METHODS: We acquired fMRI data from 29 PSZ and 36 controls performing the Temporal Utility Integration decision-making task. Computational analyses estimated parameters corresponding to learning rates for both positive and negative reward prediction errors (RPEs) and the degree to which participates relied on representations of relative uncertainty. Trial-wise estimates of expected value, certainty, and RPEs were generated to model fMRI data. RESULTS: Behaviorally, PSZ demonstrated reduced reward-seeking behavior compared to controls, and negative symptoms were positively correlated with loss-avoidance behavior. This finding of a bias toward loss avoidance learning in PSZ is consistent with previous work. Surprisingly, neither behavioral measures of exploration nor neural correlates of uncertainty in the rlPFC differed significantly between groups. However, we showed that trial-wise estimates of relative uncertainty in the rlPFC distinguished participants who engaged in exploratory behavior from those who did not. rlPFC activation was positively associated with intellectual function. CONCLUSIONS: These results further elucidate the nature of reinforcement learning and decision-making in PSZ and healthy volunteers.

Uncaptured rates of postpartum venous thromboembolism: a US national analysis.

OBJECTIVE: To quantify the proportion of postpartum venous thromboembolism (VTE) readmissions, including those that occur at different hospitals from index admission, and describe risk factors for this outcome. DESIGN: Retrospective observational study. SETTING: US hospitals included in the Nationwide Readmissions Database. SAMPLE: A total of 3 719 238 patients >14 years of age with a delivery-associated hospitalisation in 2014. METHODS: Univariate analysis was performed to identify patient and hospital factors associated with readmissions. Significant factors were included in multivariate logistic regression to identify independent risk factors. Results were weighted for national estimates. MAIN OUTCOME MEASURES: Readmission with VTE to both index and different hospitals at 30, 60 and 90 days. RESULTS: The VTE cumulative readmission rate was 0.053% (n = 1477), 0.063% (n = 1765) and 0.069% (n = 1938) at 30, 60 and 90 days, respectively. Patients were readmitted to different hospitals 31% of the time within 90 days. Risk factors for different hospital VTE readmission were unique and included younger age and initial admission to a small/medium-sized hospital. Initial admission to a for-profit hospital increased the likelihood of readmission to a different hospital. CONCLUSIONS: Nearly one in three postpartum VTEs are missed by the current quality metrics, with significant implications for outcomes and quality. For-profit hospitals have a significant portion of their VTE readmissions hidden, falsely lowering their readmission rates relative to public hospitals. TWEETABLE ABSTRACT: US analysis shows 1 in 3 readmissions for postpartum venous thromboembolism currently missed.

Pharmacokinetics and pharmacodynamics of the novel monobactam LYS228 in a neutropenic murine thigh model of infection.

Objectives: The neutropenic murine thigh infection model and a dose-fractionation approach were used to determine the pharmacokinetic/pharmacodynamic (PK/PD) relationship of LYS228, a novel monobactam antibiotic with activity against Enterobacteriaceae including carbapenem-resistant strains. Methods: Mice (n = 4 per group) were inoculated with Enterobacteriaceae strains via intramuscular injection. Two hours post-bacterial inoculation, treatment with LYS228 was initiated. Animals were euthanized with CO2 24 h after the start of therapy and bacterial counts (log10 cfu) per thigh were determined. PK parameters were calculated using free (f) plasma drug levels. Results: Following a dose-fractionation study, non-linear regression analysis determined that the predominant PK/PD parameter associated with antibacterial efficacy of LYS228 was the percentage of the dosing interval that free drug concentrations remained above the MIC (%fT>MIC). In a dose-dependent manner, LYS228 reduced the thigh bacterial burden in models established with Enterobacteriaceae producing ß-lactamase enzymes of all classes (e.g. ESBLs, NDM-1, KPC, CMY-2 and OXA-48). The range of the calculated static dose was 86-649 mg/kg/day for the isolates tested, and the magnitude of the driver of efficacy was 37-83 %fT>MIC. %fT>MIC was confirmed as the parameter predominantly driving efficacy as evidenced by a strong coefficient of determination (r2 = 0.68). Neutrophils had minimal impact on the effect of LYS228 in the murine thigh infection model. Conclusions: LYS228 is efficacious in murine thigh infection models using ß-lactamase-producing strains of Enterobacteriaceae, including those expressing metallo-ß-lactamases, ESBLs and serine carbapenemases, with the PK/PD driver of efficacy identified as %T>MIC.

Motivational deficits in schizophrenia relate to abnormalities in cortical learning rate signals.

Individuals from across the psychosis spectrum display impairments in reinforcement learning. In some individuals, these deficits may result from aberrations in reward prediction error (RPE) signaling, conveyed by dopaminergic projections to the ventral striatum (VS). However, there is mounting evidence that VS RPE signals are relatively intact in medicated people with schizophrenia (PSZ). We hypothesized that, in PSZ, reinforcement learning deficits often are not related to RPE signaling per se but rather their impact on learning and behavior (i.e., learning rate modulation), due to dysfunction in anterior cingulate and dorsomedial prefrontal cortex (dmPFC). Twenty-six PSZ and 23 healthy volunteers completed a probabilistic reinforcement learning paradigm with occasional, sudden, shifts in contingencies. Using computational modeling, we found evidence of an impairment in trial-wise learning rate modulation (α) in PSZ before and after a reinforcement contingency shift, expressed most in PSZ with more severe motivational deficits. In a subsample of 22 PSZ and 22 healthy volunteers, we found little evidence for between-group differences in VS RPE and dmPFC learning rate signals, as measured with fMRI. However, a follow-up psychophysiological interaction analysis revealed decreased dmPFC-VS connectivity concurrent with learning rate modulation, most prominently in individuals with the most severe motivational deficits. These findings point to an impairment in learning rate modulation in PSZ, leading to a reduced ability to adjust task behavior in response to unexpected outcomes. At the level of the brain, learning rate modulation deficits may be associated with decreased involvement of the dmPFC within a greater RL network.

Identification of young-of-the-year great hammerhead shark Sphyrna mokarran in northern Florida and South Carolina.

Two sharks, visually identified in the field as young-of-the-year (YOY) scalloped hammerhead Sphyrna lewini, were identified as great hammerhead Sphyrna mokarran based on nuclear-encoded single nucleotide polymorphisms (SNP) and sequences of mtDNA. Individuals were captured and released in Bulls Bay, SC, and Saint Joseph Bay, FL, in 2013 and 2014, respectively. These findings indicate S. mokarran may be pupping in or around these areas and highlight new regions that may be a productive focus for future research on early life history of S. mokarran.

Changes in Object Relations over the Course of Psychodynamic Psychotherapy.

This study explores whether object relations (OR) functioning improves over the course of psychodynamic psychotherapy, and whether this improvement is related to symptom decrease as well as therapist technique. The sample consisted of 75 outpatients engaged in short-term psychodynamic psychotherapy at a university-based psychological service clinic. OR functioning was assessed pre- and post-treatment by independent raters using the Social Cognition and Object Relations Scale from in-session patient relational narratives. The Comparative Psychotherapy Process Scale was used to assess therapist activity and psychotherapy techniques early in treatment. Independent clinical ratings of global OR and psychotherapy techniques were conducted, and rater agreement was found to be in the excellent range. Regarding the results, global OR (overall quality and level of interpersonal functioning) significantly improved with large effect size after psychodynamic therapy. Change in global OR functioning was significantly and positively related to the incidence of psychodynamic techniques in early sessions, as were number of psychotherapy sessions attended. Patient self-reported reliable change in symptomatology and reliable change in global OR were significantly related as well. Multilevel model analyses confirmed pairwise correlations accounting for therapist effects on a variety of process-outcome measures, number of sessions attended, initial levels of psychiatric symptoms, employment of therapeutic techniques as well overall OR functioning at outcome. Limitations of the present study, future research directions and implications for clinical practice are also discussed. Copyright © 2016 John Wiley & Sons, Ltd. KEY PRACTITIONER MESSAGE: Psychodynamic psychotherapy seems to be effective in improving object relations functioning. Consider use of psychodynamic techniques early in treatment with patients expressing more pathological object representations. Improvements in object relations functioning during psychodynamic psychotherapy are also related to adaptive changes in patient self-reported symptomatology. Therapist effects were also present for the study. As such therapists should be mindful to assess patient change and their use of technique at several points in treatment and flexibly adjust their approach as necessary.

Reproductive outcomes in oocyte donation cycles are associated with donor BMI.

STUDY QUESTION: When adjusting for recipient BMI, is donor body mass index (BMI) associated with IVF outcomes in donor oocyte IVF cycles? SUMMARY ANSWER: Increasing oocyte donor BMI is associated with a reduction in clinical pregnancy and live birth rates. WHAT IS KNOWN ALREADY: Increased BMI has been associated with suboptimal reproductive outcomes, particularly in assisted reproductive technology (ART) cycles. However, it remains unclear if this association implies an effect of BMI on oocyte quality and/or endometrial receptivity. STUDY DESIGN, SIZE, DURATION: A retrospective cohort study of two hundred and thirty five consecutive fresh donor oocyte IVF cycles from 1 January 2007 through 31 December 2013 at the Massachusetts General Hospital (MGH) Fertility Center. PARTICIPANTS/MATERIALS, SETTING, METHODS: Analyses included a total of 202 oocyte donors and 235 total cycles. Following adjustments for recipient BMI, the relationship between donor BMI (categorized into quartiles) and IVF outcomes was assessed. MAIN RESULTS AND THE ROLE OF CHANCE: In the entire (anonymous and known) donor population, a reduced odds of clinical pregnancy (P-trend = 0.046) and live birth (P-trend = 0.06) was observed with increasing BMI quartile. Compared with quartile 1 (BMI 17.8-21.1), odds ratio (OR) (95% CI) of clinical pregnancy was 0.9 (0.4-2.0), 0.5 (0.2-1.1) and 0.5 (0.2-1.1), and OR of live birth was 1.1 (0.5-2.6), 0.6 (0.3-1.2) and 0.6 (0.3-1.2) for quartiles 2 through 4 respectively. In anonymous donors only, the odds of clinical pregnancy (P-trend = 0.02) and live birth (P-trend = 0.03) also declined as BMI quartile increased. Compared with quartile 1 (BMI 17.8-21.1), odds ratio (OR) (95% CI) of clinical pregnancy was 0.7 (0.3-1.7), 0.5 (0.2-1.1) and 0.4 (0.1-0.9), and OR of live birth was 0.9 (0.4-2.2), 0.5 (0.3-1.2) and 0.4 (0.2-1.1) for quartiles 2 through 4 respectively. LIMITATIONS, REASONS FOR CAUTION: Limitations include the retrospective design, sample size and data from a single institution. Clinical application may not be limited to oocyte donors, though caution should be used prior to applying these principles to the general population. Data should not be interpreted to mean that all oocyte donors should be restricted to a BMI of less than 21.2 kg/m(2). WIDER IMPLICATIONS OF THE FINDINGS: Following adjustments for the respective BMI of the oocyte donor and recipient, this study demonstrates an association of preconception BMI with subsequent IVF outcomes. The observations of this study are consistent with prior animal studies, suggest a possible effect of BMI at the oocyte level prior to fertilization and implantation, and warrant further investigation. STUDY FUNDING/COMPETING INTERESTS: None.

A method for detecting recent changes in contemporary effective population size from linkage disequilibrium at linked and unlinked loci.

Estimation of contemporary effective population size (Ne) from linkage disequilibrium (LD) between unlinked pairs of genetic markers has become an important tool in the field of population and conservation genetics. If data pertaining to physical linkage or genomic position are available for genetic markers, estimates of recombination rate between loci can be combined with LD data to estimate contemporary Ne at various times in the past. We extend the well-known, LD-based method of estimating contemporary Ne to include linkage information and show via simulation that even relatively small, recent changes in Ne can be detected reliably with a modest number of single-nucleotide polymorphism (SNP) loci. We explore several issues important to interpretation of the results and quantify the bias in estimates of contemporary Ne associated with the assumption that all loci in a large SNP data set are unlinked. The approach is applied to an empirical data set of SNP genotypes from a population of a marine fish where a recent, temporary decline in Ne is known to have occurred.

Genetic variation of Prochilodus lineatus (Valenciennes, 1836) from Paraná, Baía, Miranda, and Corumbá rivers, Brazil.

The curimbatá (Prochilodus lineatus) is one of the migratory species in the Paraná River Basin impacted by the construction of dams. Mitochondrial DNA sequences and random amplified polymorphic DNA (RAPD) fragments were used to investigate genetic variability and geographic structure of five populations of curimbatá from the Paraná River Basin. A total of 1815 bp from seven polymerase chain reaction-amplified fragments representing five protein-coding mitochondrial genes were sequenced from 12 individuals. Estimates of nucleotide sequence divergence ranged from 0.00 to 0.95%. A total of 86 RAPD markers from 58 individuals were detected. Results from the Fisher exact test indicated that P. lineatus is not genetically subdivided, although significant differences in the frequencies of a few RAPD fragments were observed. This study provides useful information for stocking and management programs for resource planning of P. lineatus.

Selection and sex-biased dispersal in a coastal shark: the influence of philopatry on adaptive variation.

Sex-biased dispersal is expected to homogenize nuclear genetic variation relative to variation in genetic material inherited through the philopatric sex. When site fidelity occurs across a heterogeneous environment, local selective regimes may alter this pattern. We assessed spatial patterns of variation in nuclear-encoded, single nucleotide polymorphisms (SNPs) and sequences of the mitochondrial control region in bonnethead sharks (Sphyrna tiburo), a species thought to exhibit female philopatry, collected from summer habitats used for gestation. Geographic patterns of mtDNA haplotypes and putatively neutral SNPs confirmed female philopatry and male-mediated gene flow along the northeastern coast of the Gulf of Mexico. A total of 30 outlier SNP loci were identified; alleles at over half of these loci exhibited signatures of latitude-associated selection. Our results indicate that in species with sex-biased dispersal, philopatry can facilitate sorting of locally adaptive variation, with the dispersing sex facilitating movement of potentially adaptive variation among locations and environments.

Latent structure of cognition in schizophrenia: a confirmatory factor analysis of the MATRICS Consensus Cognitive Battery (MCCB).

BACKGROUND: The number of separable cognitive dimensions in schizophrenia has been debated. Guided by the extant factor analytic literature, the NIMH Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative selected seven cognitive domains relevant to treatment studies in schizophrenia: speed of processing, attention/vigilance, working memory, verbal learning, visual learning, reasoning and problem solving, and social cognition. These domains are assessed in the MATRICS Consensus Cognitive Battery (MCCB). The aim of this study was to conduct a confirmatory factor analysis (CFA) of the beta battery of the MCCB to compare the fit of the MATRICS consensus seven-domain model to other models in the current literature on cognition in schizophrenia. METHOD: Using data from 281 schizophrenia outpatients, we compared the seven correlated factors model with alternative models. Specifically, we compared the 7-factor model to (a) a single-factor model, (b) a three correlated factors model including speed of processing, working memory, and general cognition, and (c) a hierarchical model in which seven first-order factors loaded onto a second-order general cognitive factor. RESULTS: Multiple fit indices indicated the seven correlated factors model was the best fit for the data and provided significant improvement in model fit beyond the comparison models. CONCLUSIONS: These results support the assessment of these seven cognitive dimensions in clinical trials of interventions to improve cognition in schizophrenia. Because these cognitive factors are separable to some degree, it is plausible that specific interventions may have differential effects on the domains.

Contemporary population structure and post-glacial genetic demography in a migratory marine species, the blacknose shark, Carcharhinus acronotus.

Patterns of population structure and historical genetic demography of blacknose sharks in the western North Atlantic Ocean were assessed using variation in nuclear-encoded microsatellites and sequences of mitochondrial (mt)DNA. Significant heterogeneity and/or inferred barriers to gene flow, based on microsatellites and/or mtDNA, revealed the occurrence of five genetic populations localized to five geographic regions: the southeastern U.S Atlantic coast, the eastern Gulf of Mexico, the western Gulf of Mexico, Bay of Campeche in the southern Gulf of Mexico and the Bahamas. Pairwise estimates of genetic divergence between sharks in the Bahamas and those in all other localities were more than an order of magnitude higher than between pairwise comparisons involving the other localities. Demographic modelling indicated that sharks in all five regions diverged after the last glacial maximum and, except for the Bahamas, experienced post-glacial, population expansion. The patterns of genetic variation also suggest that the southern Gulf of Mexico may have served as a glacial refuge and source for the expansion. Results of the study demonstrate that barriers to gene flow and historical genetic demography contributed to contemporary patterns of population structure in a coastal migratory species living in an otherwise continuous marine habitat. The results also indicate that for many marine species, failure to properly characterize barriers in terms of levels of contemporary gene flow could in part be due to inferences based solely on equilibrium assumptions. This could lead to erroneous conclusions regarding levels of connectivity in species of conservation concern.

Parthenogenesis in a whitetip reef shark Triaenodon obesus involves a reduction in ploidy.

Genetic analysis of a female whitetip reef shark Triaenodon obesus and her stillborn pup, assumed to be of parthenogenetic origin, revealed that the pup was homozygous at all 24 nuclear-encoded microsatellites assayed, consistent with the idea that diploidy in the pup had been restored via terminal fusion. Flow cytometric analysis, however, indicated that the genome size of the pup was no more than half that of the mother, and microscopy revealed that nuclear volume was c. 1.73 times larger in the mother than in the pup. Together these data suggest that the pup was genetically haploid, developing directly from an unfertilized egg; as far as is known, this is the first observation of a spontaneously produced haploid vertebrate.

The effect of physicians' body weight on patient attitudes: implications for physician selection, trust and adherence to medical advice.

BACKGROUND: Research has documented negative stigma by health providers toward overweight and obese patients, but it is unknown whether physicians themselves are vulnerable to weight bias from patients. PURPOSE: This study assessed public perceptions of normal weight, overweight or obese physicians to identify how physicians' body weight affects patients' selection, trust and willingness to follow the medical advice of providers. METHODS: An online sample of 358 adults were randomly assigned to one of three survey conditions in which they completed a questionnaire assessing their perceptions of physicians who were described as normal weight, overweight or obese. Participants also completed a measure of explicit weight bias (Fat Phobia Scale) to determine whether antifat attitudes are associated with weight-related perceptions of physicians. RESULTS: Respondents reported more mistrust of physicians who are overweight or obese, were less inclined to follow their medical advice, and were more likely to change providers if the physician was perceived to be overweight or obese, compared to normal-weight physicians who elicited significantly more favorable reactions. These weight biases remained present regardless of participants' own body weight. Inspection of interaction effects revealed opposing effects of weight bias between the obese/overweight and normal-weight physician conditions. Stronger weight bias led to higher trust, more compassion, more inclination to follow advice, and less inclination to change doctors when the physician was presented as normal weight. In contrast, stronger weight bias led to less trust, less compassion, less inclination to follow advice and higher inclination to change doctors when the physician was presented as obese. CONCLUSIONS: This study suggests that providers perceived to be overweight or obese may be vulnerable to biased attitudes from patients, and that providers' excess weight may negatively affect patients' perceptions of their credibility, level of trust and inclination to follow medical advice.

Does mating behaviour affect connectivity in marine fishes? Comparative population genetics of two protogynous groupers (Family Serranidae).

Pelagic larval duration (PLD) has been hypothesized to be the primary predictor of connectivity in marine fishes; however, few studies have examined the effects that adult reproductive behaviour may have on realized dispersal. We assessed gene flow (connectivity) by documenting variation in microsatellites and mitochondrial DNA sequences in two protogynous species of groupers, the aggregate spawning red hind, Epinephelus guttatus, and the single-male, harem-spawning coney, Cephalopholis fulva, to ask whether reproductive strategy affects connectivity. Samples of both species were obtained from waters off three islands (Puerto Rico, St. Thomas and St. Croix) in the Caribbean Sea. Despite the notion that aggregate spawning of red hind may facilitate larval retention, stronger signals of population structure were detected in the harem-spawning coney. Heterogeneity and/or inferred barriers, based on microsatellites, involved St. Croix (red hind and coney) and the west coast of Puerto Rico (coney). Heterogeneity and/or inferred barriers, based on mitochondrial DNA, involved St. Croix (coney only). Genetic divergence in both species was stronger for microsatellites than for mitochondrial DNA, suggesting sex-biased dispersal in both species. Long-term migration rates, based on microsatellites, indicated asymmetric gene flow for both species in the same direction as mean surface currents in the region. Red hind had higher levels of variation in microsatellites and lower levels of variation in mitochondrial DNA. Long-term effective size and effective number of breeders were greater for red hind; estimates of θ(f) , a proxy for long-term effective female size, were the same in both species. Patterns of gene flow in both species appear to stem in part from shared aspects of larval and adult biology, local bathymetry and surface current patterns. Differences in connectivity and levels of genetic variation between the species, however, likely stem from differences in behaviour related to reproductive strategy.

Cognition in schizophrenia and schizo-affective disorder: impairments that are more similar than different.

BACKGROUND: Cognition is increasingly being recognized as an important aspect of psychotic disorders and a key contributor to functional outcome. In the past, comparative studies have been performed in schizophrenia and schizo-affective disorder with regard to cognitive performance, but the results have been mixed and the cognitive measures used have not always assessed the cognitive deficits found to be specific to psychosis. A set of optimized cognitive paradigms designed by the Cognitive Neuroscience Test Reliability and Clinical Applications for Schizophrenia (CNTRACS) Consortium to assess deficits specific to schizophrenia was used to measure cognition in a large group of individuals with schizophrenia and schizo-affective disorder. METHOD: A total of 519 participants (188 with schizophrenia, 63 with schizo-affective disorder and 268 controls) were administered three cognitive paradigms assessing the domains of goal maintenance in working memory, relational encoding and retrieval in episodic memory and visual integration. RESULTS: Across the three domains, the results showed no major quantitative differences between patient groups, with both groups uniformly performing worse than healthy subjects. CONCLUSIONS: The findings of this study suggests that, with regard to deficits in cognition, considered a major aspect of psychotic disorder, schizophrenia and schizo-affective disorder do not demonstrate major significant distinctions. These results have important implications for our understanding of the nosological structure of major psychopathology, providing evidence consistent with the hypothesis that there is no natural distinction between cognitive functioning in schizophrenia and schizo-affective disorder.

Effect of gender and race on the week 48 findings in treatment-naïve, HIV-1-infected patients enrolled in the randomized, phase III trials ECHO and THRIVE.

OBJECTIVES: A week 48 efficacy and safety analysis with respect to gender and race was conducted using pooled data from the phase III, double-blind, double-dummy efficacy comparison in treatment-naïve, HIV-infected subjects of TMC278 and efavirenz (ECHO) and TMC278 against HIV, in a once-daily regimen versus efavirenz (THRIVE) trials. METHODS: Treatment-naïve, HIV-1-infected adults were randomized to receive rilpivirine (RPV; TMC278) 25 mg once a day (qd), or efavirenz (EFV) 600 mg qd, plus tenofovir/emtricitabine (ECHO) or tenofovir/emtricitabine, zidovudine/lamivudine or abacavir/lamivudine (THRIVE). RESULTS: A total of 1368 participants (76% male and 61% White, of those with available race data) were randomized and treated. No gender-related differences in response rate (percentage of patients with HIV-1 viral load < 50 HIV-1 RNA copies/mL, using an intent-to-treat, time-to-loss-of-virological-response algorithm) were observed (RPV: men, 85%; women, 83%; EFV: men, 82%; women, 83%). Response rates were lower in Black compared with Asian and White participants (RPV: 75% vs. 95% and 85%, respectively; EFV: 74% vs. 93% and 83%, respectively); this finding was mostly a result of higher discontinuation and virological failure rates in Black patients. Safety findings were generally similar across race and gender subgroups. However, nausea occurred more commonly in women than in men in both treatment groups. In men, diarrhoea was more frequent in the EFV group, and abnormal dreams/nightmares were more frequent in men in both the EFV and RPV groups. CONCLUSIONS: Overall response rates were high for both RPV and EFV. No gender differences were observed. However, response rates were lower among Black patients, regardless of treatment group. Gender appeared to influence the incidence of gastrointestinal adverse events and abnormal dreams/nightmares for both treatments.

Population structure in Chilean hake Merluccius gayi as revealed by mitochondrial DNA sequences.

Genetic variation and divergence among samples of Chilean hake Merluccius gayi, from three localities off the coast of Chile and one locality off the coast of northern Peru, were assessed using sequences from the control region of mitochondrial DNA. Homogeneity tests revealed occurrence of at least three distinct genetic stocks of M. gayi within the region sampled. Factors potentially contributing to genetic divergence among M. gayi probably include hydrodynamics and behaviour.