Dorsal fin in the white shark, Carcharodon carcharias: a dynamic stabilizer for fast swimming

Transverse sections of the skin in the dorsal fin of the white shark, Carcharodon carcharias, tiger shark, Galeocerdo cuvier, and spotted raggedtooth shark, Carcharias taurus, show large numbers of dermal fiber bundles, which extend from the body into the fin. The bundles are tightly grouped together in staggered formation (not arranged in a straight line or in rows). This arrangement of dermal fibers gives tensile strength without impeding fiber movement. Tangential sections indicate that the fibers in all three species are strained and lie at angles in excess of 60 degrees . Of the three species investigated the dermal fibers in C. carcharias are the most densely concentrated and extend furthest distally along the dorsal fin. The overall results indicate that the dorsal fin of C. carcharias functions as a dynamic stabilizer and that the dermal fibers are crucial to this role. The fibers work like riggings that stabilize a ship's mast. During fast swimming, when the problems of yaw and roll are greatest, hydrostatic pressure within the shark increases and the fibers around the body, including in the dorsal fin, become taut, thereby stiffening the fin. During slow swimming and feeding the hydrostatic pressure is reduced, the fibers are slackened, and the muscles are able to exert greater bending forces on the fin via the radials and ceratotrichia. In C. carcharias there is a trade-off for greater stiffness of the dorsal fin against flexibility.     

Multilevel genetic analyses of two European supercolonies of the Argentine ant, Linepithema humile

Some ants have an extraordinary unicolonial social organization, whereby individuals mix freely among physically separated nests. Recently, it was shown that the European population of Linepithema humile consisted of two enormous unicolonial supercolonies. Workers of the same supercolony are never aggressive to each other. In contrast, aggressiveness is invariably high between workers from different supercolonies. Here we investigated whether gene flow occurs between two supercolonies. We identified a contact zone in which we sampled 46 nests. For each nest, aggression tests were conducted against workers from reference nests from both supercolonies. Workers were always very aggressive towards workers of one of the supercolonies but not to workers of the other. Thus, all nests could be clearly assigned to one of the two supercolonies. For 22 of the 46 nests, we genotyped 15-16 workers at five microsatellite loci. A four-level hierarchical analysis of variance revealed very strong genetic differentiation between the two supercolonies (F(SUPERCOLONY-TOTAL) = 0.541) and low differentiation between sectors (i.e. group of nests connected together with trails) within supercolonies (F(SECTOR-SUPERCOLONY) = 0.064). The very high differentiation between the two supercolonies indicates a lack of ongoing gene flow, a conclusion further bolstered by the finding that the two supercolonies share no common alleles at two of the five microsatellite loci. A Bayesian clustering method also revealed the occurrence of two distinct clusters. These clusters exactly match the grouping obtained by aggression tests. None of the 332 genotyped individuals were admixed despite the fact that some nests of the two supercolonies were separated by less than 30 m. These results demonstrate that the two supercolonies have completely separate gene pools.     

Nonparametric estimation of ROC curves in the absence of a gold standard

In the evaluation of diagnostic accuracy of tests, a gold standard on the disease status is required. However, in many complex diseases, it is impossible or unethical to obtain such a gold standard. If an imperfect standard is used, the estimated accuracy of the tests would be biased. This type of bias is called imperfect gold standard bias. In this article we develop a nonparametric maximum likelihood method for estimating ROC curves and their areas of ordinal-scale tests in the absence of a gold standard. Our simulation study shows that the proposed estimators for the ROC curve areas have good finite-sample properties in terms of bias and mean squared error. Further simulation studies show that our nonparametric approach is comparable to the binormal parametric method, and is easier to implement. Finally, we illustrate the application of the proposed method in a real clinical study on assessing the accuracy of seven specific pathologists in detecting carcinoma in situ of the uterine cervix.     

Larval morphology, genetic divergence, and contrasting levels of host manipulation between forms of Pomphorhynchus laevis (Acanthocephala)

Studies on parasite species with a wide geographic and ecological range may be confounded by still equivocal taxonomic identification. Here, we investigated genetic polymorphism and behavioural changes induced in a common intermediate host, in two different forms of Pomphorhynchus laevis based on the morphology of the larval infective stage (cystacanth). A 'smooth type' (S) and a 'wrinkled type' (W) of cystacanth were distinguished based on their surface and shape. We analysed sequence divergence at both nuclear (ribosomal gene 18S rDNA, and ribosomal internal transcribed spacers, ITS1/ITS2) and mitochondrial (cytochrome c oxidase subunit 1) genes of P. laevis cystacanths and adults at various geographical scales. A high level of sequence divergence at ITS1, ITS2 and cytochrome c oxidase subunit 1 (11, 8 and 20%, respectively) was found between these two forms. The divergence pattern consistently discriminated two groups independently of geographic origin or host, and was congruent with larval morphology. The two forms also strongly differed in the intensity of behavioural change induced in their common intermediate host, Gammarus pulex, with the S-type parasite inducing a positive phototactism, whereas W-type infected gammarids were as photophylic as uninfected ones. Overall, our data strongly support the specific status of these two forms. We suggest that smooth cystacanths correspond to P. laevis, whereas wrinkled cystacanths might correspond to the previously described and poorly documented, Pomphorhynchus tereticollis, considered a synonym of P. laevis. This study also confirms the value of a joint analysis of internal transcribed spacers and cytochrome c oxidase subunit 1 genes to biogeographic studies on these species. Finally, we emphasize the importance of linking morphological and biological characteristics of acanthocephalan cystacanths to molecular data, in the study of the evolutionary ecology and systematics of this group.     

chifish: a computer program testing for genetic heterogeneity at multiple loci using chi‐square and Fisher's exact test

chifish is a 32‐bit Windows/DOS program evaluating divergence at multiple gene loci. It tests the hypothesis of no difference at any locus both by means of Pearson's traditional chi‐square and by using Fisher's method of combining P values obtained by Fisher's exact test. Input data are read from a file formatted for genepop . Commonly used population genetics software do not perform chi‐square tests, and the simultaneous application of both techniques aids in situations where poor power of the ‘exact approach’ may prevent detection of true differentiation (e.g. few populations and few alleles per locus).     

Thermal ecology of natterjack toads (Bufo calamita) in a semiarid landscape

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To monitor the seasonal variation of body temperature (t_b) in free-ranging adult Bufo calamita, 15 toads were radio-tracked at Mas de Melons (Catalonia, Spain) using temperature-sensitive transmitters implanted to the abdominal cavity.     

莫诺苷对大鼠局灶性脑缺血再灌注损伤神经功能的影响

目的观察中药山茱萸的有效成分莫诺苷对大鼠局灶性脑缺血再灌注后神经功能的影响。方法Wistar雄性大鼠随机分为假手术组、模型组、莫诺苷小剂量组（30 mg/kg）、莫诺苷中剂量组（90 mg/kg）、莫诺苷大剂量组（270 mg/kg）、维生素E（VE）（35 mg/kg）,采用线栓法制作大鼠局灶性脑缺血再灌注模型,缺血30 min后再灌注3 d,应用Zea Longa法、爬网格、平行木、吊绳、Ludmila Belayev 12分评分法,观察莫诺苷对神经功能缺损的改善作用。结果与模型组比较,莫诺苷给药组（小、中、大剂量）Zea Longa法评分均差异极显著（P〈0.01）;与模型组比较,莫诺苷给药组（小、中、大剂量）吊绳法评分均差异极显著（P〈0.01）;Ludmila Belayev 12分评分法评分与模型组比较,莫诺苷大剂量组差异极显著（P〈0.001）,中剂量组差异极显著（P〈0.01）。结论莫诺苷对局灶性脑缺血再灌注模型大鼠有改善行为学评分的作用。     

The influence of phylogenetic uncertainty on the detection of positive Darwinian selection

The power of maximum likelihood tests of positive selection on protein-coding genes depends heavily on detecting and accounting for potential biases in the studied data set. Although the influence of transition:transversion and codon biases have been investigated in detail, little is known about how inaccuracy in the phylogeny used during the calculations affects the performance of these tests. In this study, 3 empirical data sets are analyzed using sets of simulated topologies corresponding to low, intermediate, and high levels of phylogenetic uncertainty. The detection of positive selection was largely unaffected by errors in the underlying phylogeny. However, the number of sites identified as being under positive selection tended to be overestimated.     

Media- and method-dependent variations in minimal inhibitory concentrations of antiplaque agents on oral bacteria

AIMS: To determine minimal inhibitory concentrations (MICs) and the percentage of nonsusceptible bacteria-- those still cultivable above a threshold concentration--in human supragingival dental plaque and saliva for antiplaque/antimicrobial agents including triclosan (TCS) and trichlorocarbanilide (TCC), and a new potential antimicrobial, 2-t-butyl-5-(4-t-butylphenyl)-phenol (DTBBP). METHODS AND RESULTS: Broth and agar dilution-based MIC tests were performed using 28 oral and nonoral bacterial strains representing 17 species. MICs for TCS were lowest and more than 100-fold lower than DTBBP (P < 0.0005) by both methods. MICs for TCS were lower in broth-based tests compared with TCC. The additions of defibrinated blood to agar and horse serum to broth increased MICs--in the case of TCS, 10- to 15-fold. Significantly higher proportions of nonsusceptible plaque and salivary bacteria were recovered from agar media containing DTBBP or TCC compared with TCS (P < 0.05). CONCLUSIONS: TCS is a more effective antimicrobial agent than either TCC or DTBBP as determined by in vitro testing. SIGNIFICANCE AND IMPACT OF THE STUDY: The utility of in vitro testing for antiplaque agents as a predictor of in vivo efficacy is affected by the methods used.     

An adaptive test for a subset of coefficients in a multivariate regression model

An adaptive multivariate test is proposed for a subset of regression coefficients in a linear model. This adaptive method uses the studentized deleted residuals to calculate an appropriate weight for each observation. The weights are then used to compute Wilk's lambda for the weighted model. The adaptive test is performed by permuting the independent variables corresponding to those parameters that are assumed to equal zero in the null hypothesis. The permuted variables are then weighted to obtain a permutation test statistic that is used to estimate the p-value. An example is presented of a multivariate regression that uses systolic and diastolic blood pressure as dependent variables with age and body mass index as independent variables. The simulation results show that the adaptive test maintains its size for the three multivariate error distributions that were used in the study. For normal error models the power of the adaptive test nearly equaled that of the non-adaptive test. For models that used non-normal errors the adaptive test was considerably more powerful than the traditional non-adaptive test.