Optimizing purebred selection for crossbred performance using QTL with different degrees of dominance

A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing.     

Drought and the organization of tree-hole mosquito communities

Summary In southeastern North America (North Florida, USA), the duration, frequency, and timing of drought differentially affect the survivorship of pre-adult tree-hole mosquitoes. Drought affects survivorship both by the direct action of dehydration on developing larvae and pupae and by the indirect modulation of predation. The drought-susceptible species, Toxorhynchites rutilus, Orthopodomyia signifera, and Anopheles barberi co-occur in more permanent holes that are larger, with larger, more vertical openings, lower down in larger trees, and contain darker water with higher conductivity, pH, and tannin-lignin content than the holes occupied by Aedes triseriatus that has drought-resistant eggs and rapid larval development. Ovipositing mosquitoes cue on physical and chemical attributes of tree holes independently of host tree species. These same attributes differ among drought-prone and drought-resistant holes but mosquitoes track these attributes more faithfully than the attributes predict tree-hole stability.     

Effect of postnatal development on calcium currents and slow charge movement in mammalian skeletal muscle

Single- (whole-cell patch) and two-electrode voltage-clamp techniques were used to measure transient (Ifast) and sustained (Islow) calcium currents, linear capacitance, and slow, voltage-dependent charge movements in freshly dissociated fibers of the flexor digitorum brevis (FDB) muscle of rats of various postnatal ages. Peak Ifast was largest in FDB fibers of neonatal (1-5 d) rats, having a magnitude in 10 mM external Ca of 1.4 +/- 0.9 pA/pF (mean +/- SD; current normalized by linear fiber capacitance). Peak Ifast was smaller in FDB fibers of older animals, and by approximately 3 wk postnatal, it was so small as to be unmeasurable. By contrast, the magnitudes of Islow and charge movement increased substantially during postnatal development. Peak Islow was 3.6 +/- 2.5 pA/pF in FDB fibers of 1-5-d rats and increased to 16.4 +/- 6.5 pA/pF in 45-50-d-old rats; for these same two age groups, Qmax, the total mobile charge measurable as charge movement, was 6.0 +/- 1.7 and 23.8 +/- 4.0 nC/microF, respectively. As both Islow and charge movement are thought to arise in the transverse-tubular system, linear capacitance normalized by the area of fiber surface was determined as an indirect measure of the membrane area of the t-system relative to that of the fiber surface. This parameter increased from 1.5 +/- 0.2 microF/cm2 in 2-d fibers to 2.9 +/- 0.4 microF/cm2 in 44-d fibers. The increases in peak Islow, Qmax, and normalized linear capacitance all had similar time courses. Although the function of Islow is unknown, the substantial postnatal increase in its magnitude suggests that it plays an important role in the physiology of skeletal muscle.     

Comparative glucose and pentose utilization by a thermophilic Lactobacillus

Abstract A thermophilic Lactobacillus , isolate VB183, was tested for comparative glucose and pentose utilization. The possible adverse effect of high concentrations of metabolic end products on cell yield was lessened or eliminated by using low substrate concentrations. Possible growth due to intracellular reserve material, was counteracted by starving the cells for 90 min before being used as inoculant. Isolate VB183 exhibited a higher growth rate on glucose (μ= 1.08 h⁻¹) than on ribose (μ= 0.76 h⁻¹). L. salivarius was included as a pentose non-fermenting control and showed no significant difference between growth on basal medium with and without ribose. VB183 was also found to utilize l (+)-arabinose but not d (−)-arabinose, stressing the importance of the isomer of the sugars tested.     

Effect of pH and the bacteriocin carnocin 54 on growth and cell morphology of two Leuconostoc strains

Leuconostoc carnosum LA54A produces carnocin 54, a bacteriocin inhibitory to Listeria and closely related lactic acid bacteria. The effects of the pH of cell-free LA54 culture supernatants on the antibacterial activity of carnocin 54 was assessed using Leuc. mesenteroides DSM 20343 and TA10C as indicator strains. Carnocin 54 showed greatest activity against both strains at pH 4.5. At pH 6.5, activity was reduced, especially against Leuc. mesenteroides TA10C. Scanning electron microscopy showed irregular and rough surfaces on bacteriocin-treated cells at both pH values.     

Morphological parameters affecting false lumen thrombosis following type B aortic dissection: a systematic study based on simulations of idealized models

Type B aortic dissection (TBAD) carries a high risk of complications, particularly with a partially thrombosed or patent false lumen (FL). Therefore, uncovering the risk factors leading to FL thrombosis is crucial to identify high-risk patients. Although studies have shown that morphological parameters of the dissected aorta are related to FL thrombosis, often conflicting results have been reported. We show that recent models of thrombus evolution in combination with sensitivity analysis methods can provide valuable insights into how combinations of morphological parameters affect the prospect of FL thrombosis. Based on clinical data, an idealized geometry of a TBAD is generated and parameterized. After implementing the thrombus model in computational fluid dynamics simulations, a global sensitivity analysis for selected morphological parameters is performed. We then introduce dimensionless morphological parameters to scale the results to individual patients. The sensitivity analysis demonstrates that the most sensitive parameters influencing FL thrombosis are the FL diameter and the size and location of intimal tears. A higher risk of partial thrombosis is observed when the FL diameter is larger than the true lumen diameter. Reducing the ratio of the distal to proximal tear size increases the risk of FL patency. In summary, these parameters play a dominant role in classifying morphologies into patent, partially thrombosed, and fully thrombosed FL. In this study, we point out the predictive role of morphological parameters for FL thrombosis in TBAD and show that the results are in good agreement with available clinical studies.

     

Evolutionary Divergence of the Genetic Architecture Underlying Photoperiodism in the Pitcher-Plant Mosquito, Wyeomyia Smithii

We determine the contribution of composite additive, dominance, and epistatic effects to the genetic divergence of photoperiodic response along latitudinal, altitudinal, and longitudinal gradients in the pitcher-plant mosquito, Wyeomyia smithii. Joint scaling tests of crosses between populations showed wide-spread epistasis as well as additive and dominance differences among populations. There were differences due to epistasis between an alpine population in North Carolina and populations in Florida, lowland North Carolina, and Maine. Longitudinal displacement resulted in differences due to epistasis between Florida and Alabama populations separated by 300 km but not between Maine and Wisconsin populations separated by 2000 km. Genetic differences between New Jersey and Ontario did not involve either dominance or epistasis and we estimated the minimum number of effective factors contributing to a difference in mean critical photoperiod of 5 SD between them as n(E) = 5. We propose that the genetic similarity of populations within a broad northern region is due to their more recent origin since recession of the Laurentide Ice Sheet and that the unique genetic architecture of each population is the result of both mutation and repeated migration-founder-flush episodes during the dispersal of W. smithii in North America. Our results suggest that differences in composite additive and dominance effects arise early in the genetic divergence of populations while differences due to epistasis accumulate after more prolonged isolation.     

A study on the minimum number of loci required for genetic evaluation using a finite locus model

For a finite locus model, Markov chain Monte Carlo (MCMC) methods can be used to estimate the conditional mean of genotypic values given phenotypes, which is also known as the best predictor (BP). When computationally feasible, this type of genetic prediction provides an elegant solution to the problem of genetic evaluation under non-additive inheritance, especially for crossbred data. Successful application of MCMC methods for genetic evaluation using finite locus models depends, among other factors, on the number of loci assumed in the model. The effect of the assumed number of loci on evaluations obtained by BP was investigated using data simulated with about 100 loci. For several small pedigrees, genetic evaluations obtained by best linear prediction (BLP) were compared to genetic evaluations obtained by BP. For BLP evaluation, used here as the standard of comparison, only the first and second moments of the joint distribution of the genotypic and phenotypic values must be known. These moments were calculated from the gene frequencies and genotypic effects used in the simulation model. BP evaluation requires the complete distribution to be known. For each model used for BP evaluation, the gene frequencies and genotypic effects, which completely specify the required distribution, were derived such that the genotypic mean, the additive variance, and the dominance variance were the same as in the simulation model. For lowly heritable traits, evaluations obtained by BP under models with up to three loci closely matched the evaluations obtained by BLP for both purebred and crossbred data. For highly heritable traits, models with up to six loci were needed to match the evaluations obtained by BLP.     

Exploring Beneficial/Virulence Properties of Two Dairy-Related Strains of Streptococcus infantarius subsp. infantarius

The genus Streptococcus includes various species, remarkably different in their behavior, applications, virulence, and safety. Taxonomically Streptococcus infantarius subsp. infantarius belonging to the Streptococcus bovis group, which includes several pathogen species, however, has been found as predominant species in some African dairy products that are widely consumed and considered to be safe. Streptococcus infantarius subsp. infantarius’ safety may be questioned due to the association of this species with clinical cases. In this study, isolates from dairy origin were selected based on their bacteriocinogenic potential and differentiated by their RAPD-PCR profiles. Two strains were identified by 16S rRNA sequencing as St. infantarius subsp. infantarius and investigated regarding their potential beneficial properties and factors related to virulence and safety. A series of in vitro tests included properties related to survival in the gastrointestinal tract and beneficial intestinal activities. Production of bacteriocin/s, detection of related genes, and partial characterization of expressed antimicrobial protein were evaluated. Genes related to folate biosynthesis were detected in both studied strains. Evaluation of physiological tests related to strains virulence, adhesion, and resistance to antibiotics and detections of virulence and biogenic amines production-related genes were also investigated. Taking in consideration all the aspects of the specific nature of St. infantarius subsp. infantarius K1–4 and K5–1 (beneficial properties and virulence characteristics), both strains cannot be considered safe for human or other animals application, even though they have been isolated from dairy products. This study is highlighting the importance of evaluation for presence of potential virulence factors in newly characterized strains in order to be confident in their safety.