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Marie GB Hansen Mette Christoffersen Line R Thuesen Morten R Petersen Anders M Bojesen 《Acta veterinaria Scandinavica》2010,52(1):3
Background
Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum are able to infect horses. However, the extend to which Danish horses are infected and seroconvert due to these two bacteria is unknown. The aim of the present study was to evaluate the seroprevalence of B. burgdorferi sensu lato and A. phagocytophilum in Danish horses.Methods
A total of 390 blood samples collected from all major regions of Denmark and with a geographical distribution corresponding to the density of the Danish horse population were analyzed. All samples were examined for the presence of antibodies against B. burgdorferi sensu lato and A. phagocytophilum by the use of the SNAP®4DX ® ELISA test.Results
Overall, 29.0% of the horses were seropositive for B. burgdorferi sensu lato whereas 22.3% were seropositive for A. phagocytophilum.Conclusions
Antibodies against B burgdorferi sensu lato and A. phagocytophilum are commonly found among Danish horses thus showing that Danish horses are frequently infected by these organisms.4.
Response of grazing snails to phosphorus enrichment of modern stromatolitic microbial communities 总被引:1,自引:0,他引:1
JAMES J. ELSER JOHN H. SCHAMPEL MARCIA KYLE JAMES WATTS EVAN W. CARSON THOMAS E. DOWLING CAROL TANG PETER D. ROOPNARINE 《Freshwater Biology》2005,50(11):1826-1835
1. The effects of added phosphorus (P) on the growth, P and RNA : DNA contents, and survivorship of snails grazing on laminated microbial mats (living ‘stromatolites’) were examined in the Rio Mesquites at Cuatro Ciénegas, Mexico (total P, c. 0.60 μmol L?1) to test the hypothesis that strong P‐limitation of microautotroph growth produces a stoichiometric constraint on herbivores because of mineral P‐limitation. 2. In a 3‐week experiment performed in summer 2001, addition of phosphorus (+15 μmol L?1) resulted in a strong decline in stromatolite biomass C : P ratio from very high levels (c. 2300 : 1 by atoms) to moderate levels (c. 550 : 1). The endemic hydrobiid snail Mexithauma quadripaludium responded to P‐enrichment with elevated body P content and higher RNA : DNA ratios, especially for small animals likely to be actively growing. This positive response is consistent with the existence of a stoichiometric constraint on snail growth. 3. In a longer experiment (8 weeks) involving a more moderate P enrichment (+5 μmol L?1) in summer 2002, P enrichment reduced stromatolite C : P ratio from moderate values in control treatments (c. 750) to very low values (<100 : 1). Snails responded to stromatolite P‐enrichment with increased body P content but, in contrast to the first experiment, with lower RNA : DNA ratio, lower growth rates, and higher mortality. 4. These contrasting results suggest that both very high and very low biomass C : P ratios in stromatolites are detrimental to M. quadripaludium performance, leading us to hypothesise that these herbivores live on a ‘stoichiometric knife edge’. 相似文献
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Estimates of DNA and protein sequence divergence: an examination of some assumptions 总被引:5,自引:3,他引:2
Some of the assumptions underlying estimates of DNA and protein sequence
divergence are examined. A solution for the variance of these estimates
that allows for different mutation rates and different population sizes in
each species and for an arbitrary structure in the initial population is
obtained. It is shown that these conditions do not strongly affect
estimates of divergence. In general, they cause the variance of divergence
to be smaller than a binomial variance. Thus, the binomial variance that is
usually assumed for these estimates is safely conservative. It is shown
that variability in the mutation rate among sites can have an effect as
large as or larger than variability in the mutation rate among bases.
Variability in the mutation rate among bases and among sites causes the
number of substitutions between two sequences to be underestimated. Protein
and DNA sequences from several species are collected to estimate the
variability in mutation rates among sites. When many homologous sequences
are known, standard methods to estimate this variability can be used. The
estimates of this variability show that this factor is important when
considering the spectrum of spontaneous mutations and is strongly reflected
in the divergence of sequences. Smaller variability is found for the third
position of codons than for the first and second codon positions. This may
be because of less selective constraints on this position or because the
third position has been saturated with mutations for the sequences
examined.
相似文献
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