Common structure in panels of short ecological time-series. (25/710)

Typically, in many studies in ecology, epidemiology, biomedicine and others, we are confronted with panels of short time-series of which we are interested in obtaining a biologically meaningful grouping. Here, we propose a bootstrap approach to test whether the regression functions or the variances of the error terms in a family of stochastic regression models are the same. Our general setting includes panels of time-series models as a special case. We rigorously justify the use of the test by investigating its asymptotic properties, both theoretically and through simulations. The latter confirm that for finite sample size, bootstrap provides a better approximation than classical asymptotic theory. We then apply the proposed tests to the mink-muskrat data across 81 trapping regions in Canada. Ecologically interpretable groupings are obtained, which serve as a necessary first step before a fuller biological and statistical analysis of the food chain interaction.  (+info)

Prevalence of IgG antibodies response to Borrelia burgdorferi s.l. in populations of wild rodents from Mazury lakes district region of Poland. (26/710)

Three rodent species: Clethrionomys glareolus, Apodemus flavicollis and Microtus arvalis from Mazury Lakes District of Poland were examined for antibodies to Borrelia burgdorferi by enzyme-labelled protein G assay (ELGA). C. glareolus had an exceptionally high prevalence of B. burgdorferi antibodies - 58%, but A. flavicollis and M. arvalis also showed significant prevalence of 16.6% and 10.5%, respectively. The ELGA method is highly specific with good reproducibility. Nevertheless, some differences of sensitivity of assessed samples were season dependent. However, high seroprevalence did not coincide with infestation rates of examined rodents by I. ricinus ticks. The results indicated that in Mazury Lakes District, naturally infected rodents play an important role as an animal reservoir host for B. burgdorferi, and these animals may increase the risk of human infections in some habitats used as recreation areas. Also, this study shows that ELGA method based on the affinity of protein G for IgG of wild animals may be widely used to determine the competent zoonotic reservoir of B. burgdorferi.  (+info)

Optimal allocation of reproductive effort: manipulation of offspring number and size in the bank vole. (27/710)

The number of offspring attaining reproductive age is an important measure of an individual's fitness. However, reproductive success is generally constrained by a trade-off between offspring number and quality. We conducted a factorial experiment in order to study the effects of an artificial enlargement of offspring number and size on the reproductive success of female bank voles (Clethrionomys glareolus). We also studied the effects of the manipulations on growth, survival and reproductive success of the offspring. Potentially confounding effects of varying maternal quality were avoided by cross-fostering. Our results showed that the number of offspring alive in the next breeding season was higher in offspring number manipulation groups, despite their smaller body size at weaning. Offspring size manipulation had no effect on offspring growth or survival. Further, the first litter size of female offspring did not differ between treatments. In conclusion, females may be able to increase the number of offspring reaching reproductive age by producing larger litters, whereas increasing offspring size benefits neither the mother nor the offspring.  (+info)

Mycoplasma microti sp. nov., isolated from the respiratory tract of prairie voles (Microtus ochrogaster). (28/710)

Mycoplasmas were isolated from the respiratory tracts of prairie voles (Microtus ochrogaster). This paper presents biochemical, serological and molecular genetic characterizations of those organisms and proposes a new species, Mycoplasma microti sp. nov. The type strain of Mycoplasma microti is strain IL371T (ATCC 700935T).  (+info)

NADPH-diaphorase activity and nitric oxide synthase isoforms in the trophoblast of Calomys callosus. (29/710)

The pattern of expression of a variety of placental nitric oxide synthase isoforms has contributed to elucidating the regulatory mechanisms of nitric oxide (NO) synthesis during gestation. The maintenance of vascular tone, attenuation of vasoconstriction, prevention of platelet and leukocyte adhesion to the trophoblast surface, and possible participation in uterine blood flow seem to be the main functions of NO generated at the fetal-maternal interface in humans and mice. Extending this knowledge to other rodent species commonly used as laboratory animals, in this study we focus on NADPH-diaphorase activity and the distribution of nitric oxide synthase isoforms (NOS) in the trophoblast cells of Calomys callosus during different phases of pregnancy. NADPH-diaphorase activity was evaluated cytochemically and the presence of NOS isoforms detected by immunohistochemistry. These techniques were performed on pre- and postimplantation embryos in situ and in vitro, as well as in placentae on d 14 and 18 of pregnancy. Neither NADPH-diaphorase activity nor inducible or endothelial NOS isoforms were found in pre-implanting embryos except after culturing for at least 48 h, when some of the embryonic cells were positive for the diaphorase reaction. On d 6.5 of pregnancy, trophoblast cells showed intense diaphorase activity both in situ and under in vitro conditions. A positive reaction was also found in the different placental trophoblast cells on d 14 and 18 of pregnancy. The inducible NOS (iNOS) isoform, but not the endothelial isoform, was immunodetected in trophoblast cells from the placenta and from postimplantation embryos in situ and under in vitro conditions. These results strongly suggest the production of NO by the iNOS isoform in the trophoblast of Calomys callosus after embryo implantation. The data also emphasise a possible role for the trophoblast in producing and releasing cytotoxic molecules at the fetal-maternal interface.  (+info)

Characterization of the genomic Xist locus in rodents reveals conservation of overall gene structure and tandem repeats but rapid evolution of unique sequence. (30/710)

The Xist locus plays a central role in the regulation of X chromosome inactivation in mammals, although its exact mode of action remains to be elucidated. Evolutionary studies are important in identifying conserved genomic regions and defining their possible function. Here we report cloning, sequence analysis, and detailed characterization of the Xist gene from four closely related species of common vole (field mouse), Microtus arvalis. Our analysis reveals that there is overall conservation of Xist gene structure both between different vole species and relative to mouse and human Xist/XIST. Within transcribed sequence, there is significant conservation over five short regions of unique sequence and also over Xist-specific tandem repeats. The majority of unique sequences, however, are evolving at an unexpectedly high rate. This is also evident from analysis of flanking sequences, which reveals a very high rate of rearrangement and invasion of dispersed repeats. We discuss these results in the context of Xist gene function and evolution.  (+info)

Glacial survival of the Norwegian lemming (Lemmus lemmus) in Scandinavia: inference from mitochondrial DNA variation. (31/710)

In order to evaluate the biogeographical hypothesis that the Norwegian lemming (Lemmus lemmus) survived the last glacial period in some Scandinavian refugia, we examined variation in the nucleotide sequence of the mitochondrial control region (402 base pairs (bp)) and the cytochrome b (cyt b) region (633 bp) in Norwegian and Siberian (Lemmus sibiricus) lemmings. The phylogenetic distinction and cyt b divergence estimate of 1.8% between the Norwegian and Siberian lemmings suggest that their separation pre-dated the last glaciation and imply that the Norwegian lemming is probably a relic of the Pleistocene populations from Western Europe. The star-like control region phylogeny and low mitochondrial DNA diversity in the Norwegian lemming indicate a reduction in its historical effective size followed by population expansion. The average estimate of post-bottleneck time (19-21 kyr) is close to the last glacial maximum (18-22 kyr BP). Taking these findings and the fossil records into consideration, it seems likely that, after colonization of Scandinavia in the Late Pleistocene, the Norwegian lemming suffered a reduction in its population effective size and survived the last glacial maximum in some local Scandinavian refugia, as suggested by early biogeographical work.  (+info)

Longitudinal monitoring of the dynamics of infections due to Bartonella species in UK woodland rodents. (32/710)

Blood samples were repeatedly collected from 12 sympatric woodland rodents over a 12-month period and DNA extracts from each were incorporated into a bartonella-specific PCR targeting a fragment of the 16S/23S rRNA intergenic spacer region (ISR). The composition of each amplicon was analysed using restriction enzyme analysis (REA) and base sequence comparison. Bartonella DNA was detected in 70 of 109 samples. Eleven samples contained DNA derived from more than one strain. Sequence analysis of 62 samples found 12 sequence variants (ISR genotypes) that were provisionally assigned to 5 different species, 2 of which were newly recognized. Up to five different species were detected in each animal. On about two-thirds of occasions, a species detected I month was not there the next, but never was a genotype superseded by another of the same species. However, a genotype could be re-encountered months later in the same animal, even if interim samples contained other genotypes. Our results suggest that although most animals are bacteraemic most of the time, specific infections are often superseded and that a complex and dynamic epidemiology of bartonella bacteraemias exists in woodland rodents.  (+info)