On the quantitative genetics of mixture characters

Finite mixture models are helpful for uncovering heterogeneity due to hidden structure. Quantitative genetics issues of continuous characters having a finite mixture of Gaussian components as statistical distribution are explored in this article. The partition of variance in a mixture, the covariance between relatives under the supposition of an additive genetic model, and the offspring-parent regression are derived. Formulas for assessing the effect of mass selection operating on a mixture are given. Expressions for the genetic and phenotypic correlations between mixture and Gaussian traits and between two mixture traits are presented. It is found that, if there is heterogeneity in a population at the genetic or environmental level, then genetic parameters based on theory treating distributions as homogeneous can lead to misleading interpretations. Some peculiarities of mixture characters are: heritability depends on the mean values of the component distributions, the offspring-parent regression is nonlinear, and genetic or phenotypic correlations cannot be interpreted devoid of the mixture proportions and of the parameters of the distributions mixed.     

Global diversity of large branchiopods (Crustacea: Branchiopoda) in freshwater

With about 500 known species worldwide, the large brachiopods are a relatively small group of primitive crustaceans. With few exceptions they live in temporary aquatic systems that are most abundant in arid and semi arid areas. As many regions remain unexplored and as especially the number of species in clam shrimps and tadpole shrimps is underestimated due to difficult identification, the species list will increase with future surveys. The Branchiopoda are monophyletic, but inter-ordinal relationships, as well as many evolutionary relationships at lower taxonomic levels are still unclear. Ongoing molecular studies will more accurately depict species diversity and phylogenetic patterns. With the exception of some anostracan families, most families are not restricted to the northern or southern hemisphere or specific zoogeographical regions. Large branchiopods are used for the assessment of the quality and function of temporary wetlands. Due to the reduction in number and quality of temporary wetlands, several species became endangered and are red listed by the IUCN. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Comprehensive Bee Pathogen Screening in Belgium Reveals Crithidia mellificae as a New Contributory Factor to Winter Mortality

Since the last decade, unusually high honey bee colony losses have been reported mainly in North-America and Europe. Here, we report on a comprehensive bee pathogen screening in Belgium covering 363 bee colonies that were screened for 18 known disease-causing pathogens and correlate their incidence in summer with subsequent winter mortality. Our analyses demonstrate that, in addition to Varroa destructor, the presence of the trypanosomatid parasite Crithidia mellificae and the microsporidian parasite Nosema ceranae in summer are also predictive markers of winter mortality, with a negative synergy being observed between the two in terms of their effects on colony mortality. Furthermore, we document the first occurrence of a parasitizing phorid fly in Europe, identify a new fourth strain of Lake Sinai Virus (LSV), and confirm the presence of other little reported pathogens such as Apicystis bombi, Aphid Lethal Paralysis Virus (ALPV), Spiroplasma apis, Spiroplasma melliferum and Varroa destructor Macula-like Virus (VdMLV). Finally, we provide evidence that ALPV and VdMLV replicate in honey bees and show that viruses of the LSV complex and Black Queen Cell Virus tend to non-randomly co-occur together. We also noticed a significant correlation between the number of pathogen species and colony losses. Overall, our results contribute significantly to our understanding of honey bee diseases and the likely causes of their current decline in Europe.     

Factors associated with change in exacerbation frequency in COPD

Background

Patients with chronic obstructive pulmonary disease (COPD) can be categorized as having frequent (FE) or infrequent (IE) exacerbations depending on whether they respectively experience two or more, or one or zero exacerbations per year. Although most patients do not change category from year to year, some will, and the factors associated with this behaviour have not been examined.

Methods

1832 patients completing two year follow-up in the Evaluation of COPD Longitudinally to Identify Predictive Surrogate End-points (ECLIPSE) study were examined at baseline and then yearly. Exacerbations were defined by health care utilisation. Patient characteristics compared between those patients who did or did not change exacerbation category from year 1 to year 2.

Findings

Between years 1 and 2, 221 patients (17%) changed from IE to FE and 210 patients (39%) from FE to IE. More severe disease was associated with changing from IE to FE and less severe disease from FE to IE. Over the preceding year, small falls in FEV₁ and 6-minute walking distance were associated with changing from IE to FE, and small falls in platelet count associated with changing from FE to IE.

Conclusion

No parameter clearly predicts an imminent change in exacerbation frequency category.

Trial registration

SCO104960, clinicaltrials.gov identifier {"type":"clinical-trial","attrs":{"text":"NCT00292552","term_id":"NCT00292552"}}NCT00292552     

Electrophysiological identification of thermo- and hygro-sensitive receptor neurons on the antennae of the dragonfly Libellula depressa

Recent ultrastructural investigations on Odonata antennal flagellum describe two types of sensilla styloconica, T1 and T2. The styloconic sensilla are located in pits, at the bottom of deep cavities, and share common features typical of thermo-hygroreceptors. In order to ascertain if the Odonata antennae are involved in hygroreception and thermoreception, we carried out electrophysiological recordings (single cell recordings, SCR) from adult males and females of Libellula depressa L., 1758. After contact was established, the antenna was stimulated by rapid changes in temperature and humidity. The present research shows the occurrence of a dry (DC), a moist (MC) and a cold (CC) receptor neurons on the antennal flagellum of L. depressa. These data demonstrate for the first time the presence of functional thermo-hygroreceptors on the antennal flagellum of dragonflies. The present results extend our knowledge of the not visual sensory modalities of Odonata, a field of research unexplored so far.     

On the distance of genetic relationships and the accuracy of genomic prediction in pig breeding

Background

With the advent of genomic selection, alternative relationship matrices are used in animal breeding, which vary in their coverage of distant relationships due to old common ancestors. Relationships based on pedigree (A) and linkage analysis (G_LA) cover only recent relationships because of the limited depth of the known pedigree. Relationships based on identity-by-state (G) include relationships up to the age of the SNP (single nucleotide polymorphism) mutations. We hypothesised that the latter relationships were too old, since QTL (quantitative trait locus) mutations for traits under selection were probably more recent than the SNPs on a chip, which are typically selected for high minor allele frequency. In addition, A and G_LA relationships are too recent to cover genetic differences accurately. Thus, we devised a relationship matrix that considered intermediate-aged relationships and compared all these relationship matrices for their accuracy of genomic prediction in a pig breeding situation.

Methods

Haplotypes were constructed and used to build a haplotype-based relationship matrix (G_H), which considers more intermediate-aged relationships, since haplotypes recombine more quickly than SNPs mutate. Dense genotypes (38 453 SNPs) on 3250 elite breeding pigs were combined with phenotypes for growth rate (2668 records), lean meat percentage (2618), weight at three weeks of age (7387) and number of teats (5851) to estimate breeding values for all animals in the pedigree (8187 animals) using the aforementioned relationship matrices. Phenotypes on the youngest 424 to 486 animals were masked and predicted in order to assess the accuracy of the alternative genomic predictions.

Results

Correlations between the relationships and regressions of older on younger relationships revealed that the age of the relationships increased in the order A, G_LA, G_H and G. Use of genomic relationship matrices yielded significantly higher prediction accuracies than A. G_H and G, differed not significantly, but were significantly more accurate than G_LA.

Conclusions

Our hypothesis that intermediate-aged relationships yield more accurate genomic predictions than G was confirmed for two of four traits, but these results were not statistically significant. Use of estimated genotype probabilities for ungenotyped animals proved to be an efficient method to include the phenotypes of ungenotyped animals.     

A Non‐parametric Conditional Bivariate Reference Region with an Application to Height/Weight Measurements on Normal Girls

A conceptually simple two‐dimensional conditional reference curve is described. The curve gives a decision basis for determining whether a bivariate response from an individual is “normal” or “abnormal” when taking into account that a third (conditioning) variable may influence the bivariate response. The reference curve is not only characterized analytically but also by geometric properties that are easily communicated to medical doctors – the users of such curves. The reference curve estimator is completely non‐parametric, so no distributional assumptions are needed about the two‐dimensional response. An example that will serve to motivate and illustrate the reference is the study of the height/weight distribution of 7–8‐year‐old Danish school girls born in 1930, 1950, or 1970.     

Hygroreceptors in the larva of Libellula depressa (Odonata: Libellulidae)

Ultrastructural and electrophysiological (single-cell recordings) investigations were carried out on the coeloconic sensilla borne by the apical antenna of the larvae of Libellula depressa (Odonata: Libellulidae). These sensilla appear as pegs located in pits. One of them is a compound sensillum constituted of two fused pegs in a common pit and the other two are single pegs located in separated pits close to each other. Coeloconic sensilla show position and ultrastructural details very similar to those described in insect hygroreceptors. The electrophysiological recordings on the apical antennae of the last larval instar of L. depressa clearly show the presence of moist and dry cells responding antagonistically to humidity changes. This study gives the first evidence of hygroreceptors in dragonfly larvae and represents the first electrophysiological approach to larval sensilla of aquatic insects. The presence of hygroreceptors in L. depressa larvae is in agreement with the hygropositive response shown by these insects in laboratory and field behavioural experiments.     

Influenza B virus BM2 protein has ion channel activity that conducts protons across membranes

Successful uncoating of the influenza B virus in endosomes is predicted to require acidification of the interior of the virus particle. We report that a virion component, the BM2 integral membrane protein, when expressed in Xenopus oocytes or in mammalian cells, causes acidification of the cells and possesses ion channel activity consistent with proton conduction. Furthermore, coexpression of BM2 with hemagglutinin (HA) glycoprotein prevents HA from adopting its low-pH-induced conformation during transport to the cell surface, and overexpression of BM2 causes a delay in intracellular transport in the exocytic pathway and causes morphological changes in the Golgi. These data are consistent with BM2 equilibrating the pH gradient between the Golgi and the cytoplasm. The transmembrane domain of BM2 protein and the influenza A virus A/M2 ion channel protein both contain the motif HXXXW, and, for both proteins, the His and Trp residues are important for channel function.