Molecular characterization of 39 de novo sSMC: contribution to prognosis and genetic counselling, a prospective study.

Small supernumerary marker chromosomes (sSMCs) are structurally abnormal chromosomes that cannot be characterized by karyotype. In many prenatal cases of de novo sSMC, the outcome of pregnancy is difficult to predict because the euchromatin content is unclear. This study aimed to determine the presence or absence of euchromatin material of 39 de novo prenatally ascertained sSMC by array-comparative genomic hybridization (array-CGH) or single nucleotide polymorphism (SNP) array. Cases were prospectively ascertained from the study of 65,000 prenatal samples [0.060%; 95% confidence interval (CI), 0.042-0.082]. Array-CGH showed that 22 markers were derived from non-acrocentric markers (56.4%) and 7 from acrocentic markers (18%). The 10 additional cases remained unidentified (25.6%), but 7 of 10 could be further identified using fluorescence in situ hybridization; 69% of de novo sSMC contained euchromatin material, 95.4% of which for non-acrocentric markers. Some sSMC containing euchromatin had a normal phenotype (31% for non-acrocentric and 75% for acrocentric markers). Statistical differences between normal and abnormal phenotypes were shown for the size of the euchromatin material (more or less than 1 Mb, p = 0.0006) and number of genes (more or less than 10, p = 0.0009). This study is the largest to date and shows the utility of array-CGH or SNP array in the detection and characterization of de novo sSMC in a prenatal context.

Genetic compatibility affects division of labor in the argentine ant linepithema humile.

Division of labor is central to the organization of insect societies. Within-colony comparisons between subfamilies of workers (patrilines or matrilines) revealed genetic effects on division of labor in many social insect species. Although this has been taken as evidence for additive genetic effects on division of labor, it has never been experimentally tested. To determine the relative roles of additive and nonadditive genetic effects (e.g., genetic compatibility, epistasis, and parent-of-origin imprinting effects) on worker behavior, we performed controlled crosses using the Argentine ant Linepithema humile. Three of the measured behaviors (the efficiency to collect pupae, the foraging propensity, and the distance between non-brood-tenders and brood) were affected by the maternal genetic background and the two others (the efficiency to feed larvae and the distance between brood-tenders and brood) by the paternal genetic background. Moreover, there were significant interactions between the maternal and paternal genetic backgrounds for three of the five behaviors. These results are most consistent with parent-of-origin and genetic compatibility effects on division of labor. The finding of nonadditive genetic effects is in strong contrast with the current view and has important consequences for our understanding of division of labor in insect societies.

Genetic Polymorphisms and Susceptibility to Fungal Infections

Invasive fungal infections (IFI) are life-threatening diseases that are of particular concern in specific debilitated or immunosuppressed populations. Invasive candidiasis (IC) is the most frequent of the IFI, being one of the major causes of nosocomial bloodstream infection and a feared complication in patients with recurrent gastrointestinal surgery or prolonged stay in the intensive-care unit [1,2]. Patients with hematological malignancies or prolonged chemotherapy-induced neutropenia, and those with allogeneic hematopoietic stem cell transplantation (allo-HSCT), represent the groups at highest risk for developing invasive aspergillosis (IA), which is associated with a high mortality rate despite the increasing availability of antifungal therapies [3,4]. An increasing incidence of IA has also been reported in non-neutropenic immunosuppressed populations such as solid-organ transplant recipients or steroid-treated patients with chronic pulmonary diseases [5]. Early diagnosis of IFI is crucial for improving chances of survival [6], but is particularly challenging owing to the lack of reliable diagnostic methods [7,8]. Significant efforts during the last few decades have focused on the prevention of these severe complications. Antifungal prophylaxis in high-risk patients has been shown to reduce the incidence of IA in patients with onco-hematological malignancies [9] and that of IC in surgical intensive-care unit patients [10]. However, its widespread use raises concerns about costs, toxicity, and the risk of emergence of resistant fungal species such as non-Aspergillus moulds or non-albicansCandida spp. [4,11,12]. Prophylactic strategies usually rely on the identification of host risk factors resulting from clinical conditions (type and duration of immunosuppression, underlying diseases, and extrinsic interventions) [8,13]. Recent advances in the field of immunogenetics may change our perspective of, and approach to, preventive strategies with the identification of subgroups of patients exhibiting a genetic predisposition to IFI.

Role of CCR5 genetic polymorphisms in clinical and histological outcomes of hepatitis C

Background: The CCR5 32-base deletion (CCR5D32), which results into the expression of a non-functioning receptor, has been associated with H CV c learance a nd may influence fibrosis progression i n hepatitis C . We a ssessed t he link between C CR5D32 and c linical outcomes o f HCV. Methods: Genomic D NA was isolated and analyzed b y PCR to i dentify C CR5D32 in 1 303 anti-HCV-positive persons (161 clearers and 1142 chronically infected, 1007 with a liver biopsy). Results: Overall, 200 (15.3%) w ere heterozygote a nd 16 (1.2%) homozygote for CCR5D32. H CV c learance (by univariate) was associated with m ale sex (OR 0.633, 9 5% C I 0.428-0.935, P=0.022), HCV acquisition by blood transfusion (OR 0.360, 95% CI 0.175-0.741, P =0.0056), polymorphisms at IL28B rs12979860 ( OR 0.482, 9 5% C I 0.277-0.839, P =0.0098) a nd rs8099917 ( OR 0.291, 95% CI 0.167-0.508, P=0.000014), but not with CCR5D32. However, CCR5D32 was associated with spontaneous HCV clearance when the 482 females only w ere considered, although the number of homozygotes was small (1/427 chronic vs 3/51 clearers) (OR 24.56, 95% C I 12.5-241.4, P =0.006). T he CCR5D32 deletion was not associated with liver grading and staging scores, fibrosis progression rate, or t herapy response. Conclusions: At v ariance w ith a p revious report (Nattermann et a l, 2011), suggesting that a n on-functional CCR5 m ay hamper H CV clearance, C CR5D32 appeared to b e associated with an increased spontaneous eradication in women (but not men). Given the small number of CCR5D32 homozygote persons, these data need further validation.

Genetic dissection of sodium and potassium transport along the aldosterone-sensitive distal nephron: Importance in the control of blood pressure and hypertension.

In this review, we discuss genetic evidence supporting Guyton's hypothesis stating that blood pressure control is critically depending on fluid handling by the kidney. The review is focused on the genetic dissection of sodium and potassium transport in the distal nephron and the collecting duct that are the most important sites for the control of sodium and potassium balance by aldosterone and angiotensin II. Thanks to the study of Mendelian forms of hypertension and their corresponding transgenic mouse models, three main classes of diuretic receptors (furosemide, thiazide, amiloride) and the main components of the aldosterone- and angiotensin-dependent signaling pathways were molecularly identified over the past 20years. This will allow to design rational strategies for the treatment of hypertension and for the development of the next generation of diuretics.

Redox dysregulation and oxidative stress in schizophrenia: genetic and functional anomalies of glutathione synthesis in patients and experimental models involving GABA interneurons and NMDA receptors

Objective: Converging evidence speak in favor of an abnormal susceptibility to oxidative stress in schizophrenia. A decreased level of glutathione (GSH), the principal non-protein antioxidant and redox regulator, was observed both in cerebrospinal-fluid and prefrontal cortex of schizophrenia patients (Do et al., 2000). Results: Schizophrenia patients have an abnormal GSH synthesis most likely of genetic origin: Two independent case-control studies showed a significant association between schizophrenia and a GAG trinucleotide repeat (TNR) polymorphism in the GSH key synthesizing enzyme glutamate-cysteine-ligase (GCL) catalytic subunit (GCLC) gene. The most common TNR genotype 7/7 was more frequent in controls, whereas the rarest TNR genotype 8/8 was three times more frequent in patients. The disease-associated genotypes correlated with a decrease in GCLC protein expression, GCL activity and GSH content. Such a redox dysregulation during development could underlie the structural and functional anomalies in connectivity: In experimental models, GSH deficit induced anomalies similar to those observed in patients. (a) morphology: In animal models with GSH deficit during the development we observed in prefrontal cortex a decreased dendritic spines density in pyramidal cells and an abnormal development of parvalbumine (but not of calretinine) immunoreactive GABA interneurones in anterior cingulate cortex. (b) physiology: GSH depletion in hippocampal slices induces NMDA receptors hypofunction and an impairment of long term potentiation. In addition, GSH deficit affected the modulation of dopamine on NMDA-induced Ca 2+ response in cultured cortical neurons. While dopamine enhanced NMDA responses in control neurons, it depressed NMDA responses in GSH-depleted neurons. Antagonist of D2-, but not D1-receptors, prevented this depression, a mechanism contributing to the efficacy of antipsychotics. The redox sensitive ryanodine receptors and L-type calcium channels underlie these observations. (c) cognition: Developing rats with low [GSH] and high dopamine lead deficit in olfactory integration and in object recognition which appears earlier in males that females, in analogy to the delay of the psychosis onset between man and woman. Conclusion: These clinical and experimental evidence, combined with the favorable outcome of a clinical trial with N-Acetyl Cysteine, a GSH precursor, on both the negative symptoms (Berk et al., submitted) and the mismatch negativity in an auditory oddball paradigm supported the proposal that a GSH synthesis impairment of genetic origin represent, among other factors, one major risk factor in schizophrenia.

Genetic and phenotypic architecture of metabolic syndrome-associated components in dyslipidemic and normolipidemic subjects: the GEMS Study.

Atherogenic dyslipidemia, manifest by low HDL-cholesterol and high TG levels, is an important component of ATP-III defined metabolic syndrome. Here, we dissected the phenotypic and genetic architecture of these traits by assessing their relationships with other metabolically relevant measures, including plasma adipo-cytokines, highly sensitive C-reactive protein (hsCRP) and LDL particle size, in a large family data set (n=2800) and in an independent set of dyslipidemic cases (n=716) and normolipidemic controls (n=1073). We explored the relationships among these phenotypes using variable clustering and then estimated their genetic heritabilities and cross-trait correlations. In families, four clusters explained 61% of the total variance, with one adiposity-related cluster (including hsCRP), one BP-related cluster, and two lipid-related clusters (HDL-C, TG, adiponectin and LDL particle size; apoB and non-HDL-C). A similar structure was observed in dyslipidemic cases and normolipidemic controls. The genetic correlations in the families largely paralleled the phenotype clustering results, suggesting that common genes having pleiotropic effects contributed to the correlations observed. In summary, our analyses support a model of metabolic syndrome with two major components, body fat and lipids, each with two subcomponents, and quantifies their degree of overlap with each other and with metabolic-syndrome related measures (adipokines, LDL particle size and hsCRP).

Association Study of Common Genetic Variants and HIV-1 Acquisition in 6,300 Infected Cases and 7,200 Controls.

Multiple genome-wide association studies (GWAS) have been performed in HIV-1 infected individuals, identifying common genetic influences on viral control and disease course. Similarly, common genetic correlates of acquisition of HIV-1 after exposure have been interrogated using GWAS, although in generally small samples. Under the auspices of the International Collaboration for the Genomics of HIV, we have combined the genome-wide single nucleotide polymorphism (SNP) data collected by 25 cohorts, studies, or institutions on HIV-1 infected individuals and compared them to carefully matched population-level data sets (a list of all collaborators appears in Note S1 in Text S1). After imputation using the 1,000 Genomes Project reference panel, we tested approximately 8 million common DNA variants (SNPs and indels) for association with HIV-1 acquisition in 6,334 infected patients and 7,247 population samples of European ancestry. Initial association testing identified the SNP rs4418214, the C allele of which is known to tag the HLA-B*57:01 and B*27:05 alleles, as genome-wide significant (p = 3.6×10(-11)). However, restricting analysis to individuals with a known date of seroconversion suggested that this association was due to the frailty bias in studies of lethal diseases. Further analyses including testing recessive genetic models, testing for bulk effects of non-genome-wide significant variants, stratifying by sexual or parenteral transmission risk and testing previously reported associations showed no evidence for genetic influence on HIV-1 acquisition (with the exception of CCR5Δ32 homozygosity). Thus, these data suggest that genetic influences on HIV acquisition are either rare or have smaller effects than can be detected by this sample size.

Sudden death: ethical and legal problems of post-mortem forensic genetic testing for hereditary cardiac diseases.

Hereditary non-structural diseases such as catecholaminergic polymorphic ventricular tachycardia (CPVT), long QT, and the Brugada syndrome as well as structural disease such as hypertrophic cardiomyopathy (HCM) and arrhythmogenic right ventricular cardiomyopathy (ARVC) cause a significant percentage of sudden cardiac deaths in the young. In these cases, genetic testing can be useful and does not require proxy consent if it is carried out at the request of judicial authorities as part of a forensic death investigation. Mutations in several genes are implicated in arrhythmic syndromes, including SCN5A, KCNQ1, KCNH2, RyR2, and genes causing HCM. If the victim's test is positive, this information is important for relatives who might be themselves at risk of carrying the disease-causing mutation. There is no consensus about how professionals should proceed in this context. This article discusses the ethical and legal arguments in favour of and against three options: genetic testing of the deceased victim only; counselling of relatives before testing the victim; counselling restricted to relatives of victims who tested positive for mutations of serious and preventable diseases. Legal cases are mentioned that pertain to the duty of geneticists and other physicians to warn relatives. Although the claim for a legal duty is tenuous, recent publications and guidelines suggest that geneticists and others involved in the multidisciplinary approach of sudden death (SD) cases may, nevertheless, have an ethical duty to inform relatives of SD victims. Several practical problems remain pertaining to the costs of testing, the counselling and to the need to obtain permission of judicial authorities.

Genetic and phenotypic population divergence on a microgeographic scale in brown trout.

Salmonid populations of many rivers are rapidly declining. One possible explanation is that habitat fragmentation increases genetic drift and reduces the populations' potential to adapt to changing environmental conditions. We measured the genetic and eco-morphological diversity of brown trout (Salmo trutta) in a Swiss stream system, using multivariate statistics and Bayesian clustering. We found large genetic and phenotypic variation within only 40 km of stream length. Eighty-eight percent of all pairwise F(ST) comparisons and 50% of the population comparisons in body shape were significant. High success rates of population assignment tests confirmed the distinctiveness of populations in both genotype and phenotype. Spatial analysis revealed that divergence increased with waterway distance, the number of weirs, and stretches of poor habitat between sampling locations, but effects of isolation-by-distance and habitat fragmentation could not be fully disentangled. Stocking intensity varied between streams but did not appear to erode genetic diversity within populations. A lack of association between phenotypic and genetic divergence points to a role of local adaptation or phenotypically plastic responses to habitat heterogeneity. Indeed, body shape could be largely explained by topographic stream slope, and variation in overall phenotype matched the flow regimes of the respective habitats.

Low dispersing species : population genetic processes in space and time : the genus "Trochulus" (Gastropoda: Hygromiidae) as a case study

RÉSUMÉ Une espèce est rarement composée d'une population unique. Parce que les individus ont des capacités de dispersion limitées et que les paysages sont des mosaïques d'habitats, la plupart des espèces sont plutôt composées de sous-populations connectées par la migration. Cette variation spatiale influence directement la distribution de la variabilité génétique dans et entre les populations. Durant ce travail, nous avons abordé certains des processus populationnels qui ont joué un rôle supposé dans l'apparition de nouvelles espèces au sein du genre Trochulus. Plus précisément, nous avons tenté d'évaluer les impacts respectifs de l'isolement passé (facteurs historiques) et présent (facteurs locaux). Nous avons d'abord pu montrer que les faibles capacités de dispersion des escargots terrestres ont directement influencé leur histoire évolutive à toutes les échelles spatiales et temporelles. En réduisant l'effet homogénéisant de la migration, une faible dispersion maintient dans les populations les traces génétiques d'évènements passés. A l'échelle de la distribution globale de Trochulus villosus, ces traces ont permis de reconstruire une histoire faite d'isolements et d'expansions de populations. En combinant des données génétiques avec une modélisation de la niche climatique passée, il a été possible de proposer un scénario significativement meilleur que toutes les hypothèses alternatives que nous avons testées. A l'échelle locale par contre, l'héritage historique est difficile à distinguer de la dynamique actuelle. Ce fut le cas des lignées mitochondriales du complexe sericeus-hispidus : les deux principales lignées étaient phylogénétiquement éloignées, avaient eu des démographies passées différentes et corrélaient avec des différences morphologiques. D'un autre côté, le flux de gène nucléaire était fort, contredisant l'idée de deux espèces cryptiques isolées reproductivement. Pour pouvoir conclure à la présence ou non de deux espèces, il nous a manqué des informations locales sur la dynamique des populations et les conditions écologiques que l'on trouve dans la région d'étude. Enfin, nous avons pu souligner que la connectivité entre populations d'escargots est soumise à la qualité des habitats et à leur organisation spatiale. Les escargots sont dépendants d'un habitat et s'y adaptent, comme l'indiquent la présence de «poils » uniquement sur la coquille d'espèces vivant dans des habitats humides ou la corrélation entre morphologie et habitat au sein du complexe sericeus-hispidus. Logiquement donc, les escargots migrent préférentiellement au travers d'habitats favorables comme l'a montré la réduction de flux de gènes au travers des prairies chez T. villosus (une espèce forestière). De ces données, nous pouvons supposer que les populations d'escargots en particulier, et des espèces à faible dispersion en général, ont de fortes chances d'être affectées par les changements climatiques, avec de probables implications pour leurs histoires évolutives. SUMMARY : Species rarely consists in a single population. Because individuals have limited dispersal abilities, because landscapes are habitat patchworks, most species are made of several subpopulations connected by migration. This spatial variation has consequences on the distribution of genetic diversity within and between populations, creating a structure among the populations. During the present work, we investigated some of the population processes assumed to have played an important role on the speciation within the genus Trochulus. More specifically, we questioned the respective impacts of past (historical factors) or present (local factors) population isolations. We first could show that the poor dispersal abilities of land snails have had profound impacts on their evolutionary histories at all spatial and temporal scales. Low dispersal maintains a strong signature of past events in the populations by minimising the homogenising effects of geneflow. At the scale of Trochulus villosus global distribution, they allowed to retrieve the detailed history of this species population isolations and expansions. Combining a large genetic dataset with paleo-climatic niche modelling ended up with a historical scenario significantly better than all traditional alternatives we tested. At local scale on the contrary, past events become difficult to tease apart from ongoing processes. This was the case for the divergent mitochondria) lineages within the sericeus-hispidus complex: the two principal lineages appeared to be phylogenetically distant, to have experienced different demographic histories and to correlate with morphological differences. On the other hand, nuclear (present day) geneflow was high, contradicting the idea of two reproductively isolated cryptic species. Information on the local population dynamics and environmental conditions are lacking to be able to decide whether past isolation has indeed resulted here in new species. Finally, we emphasised the importance of the habitat types present in a landscape as well as their spatial organisation for the population connectivity of land snails. These species are tightly dependent on a habitat and adapt to it as shown by thé occurrence of hair-like structures only in species living in humid environments or by the correlation between shell morphology and habitat in the sericeus-hispidus complex. As a result, land snails preferentially migrate through favourable habitats: Trochulus villosus, a forest species, had its geneflow significantly reduced across meadows. From these data, we can hypothesise that the populations of land snails in particular and of low dispersing species in general are likely to be strongly affected by the ongoing climate changes, with potential major consequences on their evolutionary histories.

Neurally Adjusted Ventilatory Assist (NAVA) improves the matching of diaphragmatic electrical activity and tidal volume in comparison to pressure support (PS) under non invasive ventilation

INTRODUCTION. Patient-ventilator asynchrony is a frequent issue in non invasivemechanical ventilation (NIV) and leaks at the patient-mask interface play a major role in itspathogenesis. NIV algorithms alleviate the deleterious impact of leaks and improve patient-ventilator interaction. Neurally adusted ventilatory assist (NAVA), a neurally triggered modethat avoids interferences between leaks and the usual pneumatic trigger, could further improvepatient-ventilator interaction in NIV patients.OBJECTIVES. To evaluate the feasibility ofNAVAin patients receiving a prophylactic postextubationNIV and to compare the respective impact ofPSVandNAVAwith and withoutNIValgorithm on patient-ventilator interaction.METHODS. Prospective study conducted in 16 beds adult critical care unit (ICU) in a tertiaryuniversity hospital. Over a 2 months period, were included 17 adult medical ICU patientsextubated for less than 2 h and in whom a prophylactic post-extubation NIV was indicated.Patients were randomly mechanically ventilated for 10 min with: PSV without NIV algorithm(PSV-NIV-), PSV with NIV algorithm (PSV-NIV+),NAVAwithout NIV algorithm (NAVANIV-)and NAVA with NIV algorithm (NAVA-NIV+). Breathing pattern descriptors, diaphragmelectrical activity, leaks volume, inspiratory trigger delay (Tdinsp), inspiratory time inexcess (Tiexcess) and the five main asynchronies were quantified. Asynchrony index (AI) andasynchrony index influenced by leaks (AIleaks) were computed.RESULTS. Peak inspiratory pressure and diaphragm electrical activity were similar in thefour conditions. With both PSV and NAVA, NIV algorithm significantly reduced the level ofleak (p\0.01). Tdinsp was not affected by NIV algorithm but was shorter in NAVA than inPSV (p\0.01). Tiexcess was shorter in NAVA and PSV-NIV+ than in PSV-NIV- (p\0.05).The prevalence of double triggering was significantly lower in PSV-NIV+ than in NAVANIV+.As compared to PSV,NAVAsignificantly reduced the prevalence of premature cyclingand late cycling while NIV algorithm did not influenced premature cycling. AI was not affectedby NIV algorithm but was significantly lower in NAVA than in PSV (p\0.05). AIleaks wasquasi null with NAVA and significantly lower than in PSV (p\0.05).CONCLUSIONS. NAVA is feasible in patients receiving a post-extubation prophylacticNIV. NAVA and NIV improve patient-ventilator synchrony in different manners. NAVANIV+offers the best patient-ventilator interaction. Clinical studies are required to assess thepotential clinical benefit of NAVA in patients receiving NIV.

IL28B alleles associated with poor hepatitis C virus (HCV) clearance protect against inflammation and fibrosis in patients infected with non-1 HCV genotypes.

Genetic polymorphisms near IL28B are associated with spontaneous and treatment-induced clearance of hepatitis C virus (HCV), two processes that require the appropriate activation of the host immune responses. Intrahepatic inflammation is believed to mirror such activation, but its relationship with IL28B polymorphisms has yet to be fully appreciated. We analyzed the association of IL28B polymorphisms with histological and follow-up features in 2335 chronically HCV-infected Caucasian patients. Assessable phenotypes before any antiviral treatment included necroinflammatory activity (n = 1,098), fibrosis (n = 1,527), fibrosis progression rate (n = 1,312), and hepatocellular carcinoma development (n = 1,915). Associations of alleles with the phenotypes were evaluated by univariate analysis and multivariate logistic regression, accounting for all relevant covariates. The rare G allele at IL28B marker rs8099917-previously shown to be at risk of treatment failure-was associated with lower activity (P = 0.04), lower fibrosis (P = 0.02) with a trend toward lower fibrosis progression rate (P = 0.06). When stratified according to HCV genotype, most significant associations were observed in patients infected with non-1 genotypes (P = 0.003 for activity, P = 0.001 for fibrosis, and P = 0.02 for fibrosis progression rate), where the odds ratio of having necroinflammation or rapid fibrosis progression for patients with IL28B genotypes TG or GG versus TT were 0.48 (95% confidence intervals 0.30-0.78) and 0.56 (0.35-0.92), respectively. IL28B polymorphisms were not predictive of the development of hepatocellular carcinoma. CONCLUSION: In chronic hepatitis C, IL28B variants associated with poor response to interferon therapy may predict slower fibrosis progression, especially in patients infected with non-1 HCV genotypes.

Early Cretaceous radiolarians of the Northeast Indian Ocean (leg 123 - site 765, site 766 and dsdp site 261) - The Antarctic-Tethys connection

During ODP Leg 123, abundant and well-preserved Neocomian radiolarians were recovered at Site 765 (Argo Abyssal Plain) and Site 766 (lower Exmouth Plateau). Assemblages are characterized by the numerical dominance of a small number of non-tethyan forms and by the scarcity of tethyan taxa. Remarkable contrasts exist between radiolarian assemblages extracted from claystones of Site 765 and reexamined DSDP Site 26 1, and faunas recovered from radiolarian sand layers, only found at Site 765. Clay faunas are unusual in their low diversity of apparently ecologically tolerant (or solution resistant?), ubiquist species, whereas sand faunas are dominated by non-tethyan taxa. Comparisons with Sites 766 and 26 1, as well as sedimentological observations, lead to the conclusion that this faunal contrast resulted from a difference in provenance, rather than from hydraulic sorting or selective dissolution. The ranges of 27 tethyan taxa from Site 765 were compared to the tethyan radiolarian zonation by Jud (1992) by means of the Unitary Associations Method. This calculation allows to directly date the Site 765 assemblages and to estimate the amount of truncation of ranges for tethyan taxa. Over 70% of the already few tethyan species of Site 765, have truncated ranges during the Valanginian-Hauterivian. Radiolarian assemblages recovered from claystones at Sites 765 and 261 in the Argo Basin apparently reflect restricted oceanic conditions during the latest Jurassic-Barremian. Neither sedimentary facies nor faunal associations bear any resemblance to what we know from typical tethyan sequences. We conclude that the Argo Basin was paleoceanographically separated from the Tethys during the Late Jurassic and part of the Early Cretaceous by its position at higher paleolatitudes and/or by enclosing land masses. Assemblages recovered from radiolarian sand layers are dominated by non-tethyan species that are interpreted as circumantarctic. Their first appearance in the late Berriasian-early Valanginian predates the oceanization of the Indo-Australian breakup (M11, late Valanginian), but coincides with a sharp increase in margin-derived pelagic turbidites. The Indo-Australian rift zone and the adjacent margins must have been submerged deeply enough to allow an intermittent influx of circumantarctic cold water into the Argo Basin, creating increased bottom current activity. Cold-water radiolarians carried into the Argo Basin upwelled along the margin, died, and accumulated in radiolarite layers due to winnowing by bottom currents. High rates of faunal change and the sharp increase of bottom current activity are thought to be synchronous with possible pronounced late Berriasian-early Valanginian lowstands in sea level. Hypothetically, both phenomena might have been.caused by a tendency to glaciation on the Antarctic-Australian continent, which was for the first time isolated from the rest of Gondwana by oceanic seaways as a result of Jurassic-Early Cretaceous sea-floor spreading. The absence of most typical tethyan radiolarian species during the Valanginian-Hauterivian is interpreted as reflecting a time of strong influx of circumantarctic cold water following oceanization (M11) and rapid spreading between Southeast India and West Australia. The reappearance and gradual abundance/diversity increase of tethyan taxa, along with the still dominant circumantarctic species are thought to result from overall more equitable climatic conditions during the Barremian-early Aptian and from the establishment of an oceanic connection with the Tethys Ocean during the early Aptian.

Not one odour but two: A new model for nestmate recognition.

Recognition systems play a key role in a range of biological processes, including mate choice, immune defence and altruistic behaviour. Social insects provide an excellent model for studying recognition systems because workers need to discriminate between nestmates and non-nestmates, enabling them to direct altruistic behaviour towards closer kin and to repel potential invaders. However, the level of aggression directed towards conspecific intruders can vary enormously, even among workers within the same colony. This is usually attributed to differences in the aggression thresholds of individuals or to workers having different roles within the colony. Recent evidence from the weaver ant Oecophylla smaragdina suggests that this does not tell the whole story. Here I propose a new model for nestmate recognition based on a vector template derived from both the individual's innate odour and the shared colony odour. This model accounts for the recent findings concerning weaver ants, and also provides an alternative explanation for why the level of aggression expressed by a colony decreases as the diversity within the colony increases, even when odour is well-mixed. The model makes additional predictions that are easily tested, and represents a significant advance in our conceptualisation of recognition systems.