Sequence diversity of the MHC DRB gene in the Eurasian beaver (Castor fiber)

Major histocompatibility complex (MHC) genes, coding molecules which play an important role in immune response, are the most polymorphic genes known in vertebrates. However, MHC polymorphism in some species is limited. MHC monomorphism at several MHC class I and II loci was previously reported for two neighbouring northern European populations of the Eurasian beaver (Castor fiber) and reduced selection for polymorphism has been hypothesized. Here, we analysed a partial sequence of the second exon of the MHC II DRB locus from seven relict European and Asian beaver populations. We detected 10 unique alleles among 76 beavers analysed. Only a western Siberian population was polymorphic, with four alleles detected in 10 individuals. Each of the remaining populations was fixed for a different allele. Sequences showed considerable divergence, suggesting the long persistence of allelic lineages. A significant excess of nonsynonymous substitutions was detected at the antigen binding sites, indicating that sequence evolution of beaver DRB was driven by positive selection. Current MHC monomorphism in the majority of populations may be the result of the superimposition of the recent bottleneck on pre-existing genetic structure resulting from population subdivision and differential pathogen pressure.     

Selective foraging on woody plant species by the Eurasian beaver (Castor fiber) in Telemark, Norway

Beavers Castor spp. are generalist herbivores, feeding on the bark, shoots and leaves of woody plants, terrestrial herbs and forbs, ferns and aquatic vegetation. As central-place foragers, beavers move out from water to select and cut trees and vegetation, and then transport it back to their refuge. These terrestrial forays are energetically costly; therefore, beavers should concentrate their foraging activity near the central place and increase the degree of selectivity for specific sizes or species of food with increasing distance from the water. The aim of this study was to test the predictions of the central place and the optimal foraging theories for the food selection of the Eurasian beaver Castor fiber , and show the foraging preferences of the focal species in the boreal conifer forest zone of Europe. Foraging intensity by beavers and the abundance of woody species were surveyed in transects positioned randomly at seven beaver territories. In compliance with the central-place foraging theory, the foraging intensity declined with increasing distance from the river. Beavers fed preferentially on willows ( Salix ), rowan ( Sorbus ) and birches ( Betula ), although alders ( Alnus ) dominated their diet. Size selectivity showed similar patterns to previous North American studies, which were also carried out in habitats with predominantly small saplings. The probability of selection of small saplings dropped as distance increased, which is consistent with the predictions of optimal foraging models that larger prey items are more likely to be favoured with increasing provisioning distance.     

The effect of beaver (Castor fiber Linnaeus, 1758) activity on amphibian reproduction

The effect of beaver (Castor fiber Linnaeus, 1758) activity on amphibian reproduction was studied in the small river valleys in Novgorod oblast. At sites not subjected to beaver activity, the reproduction rate of amphibians was low. In spring the water in beaver ponds warms up quickly, which attracts amphibians for reproduction. The maximal abundance of tadpoles due to a high reproduction rate was observed in partially drained ponds. However, a high larvae mortality rate was often observed there. Tadpole survival in flooded and empty ponds depends on factors that are not controlled by beavers, such as geomorphology and climate.     

The history of the Eurasian Beaver Castor fiber in Scotland

In 1995 Scottish Natural Heritage proposed a feasibility study to examine the case for reintroducing the Eurasian Beaver Castor fiber to Scotland. Following IUCN guidelines, an important first step is to demonstrate that the Beaver was once a native of Scotland and that the causes of its extinction no longer pose any threat to reintroduced animals. Therefore, palaeontological, archaeological and historical evidence for the former existence of the Beaver in Scotland and the causes of its extinction are reviewed.
Palaeontological and archaeological evidence suggest that the Eurasian Beaver was once widely distributed throughout mainland Scotland. Historical evidence suggests that although it was once probably fairly common, it became extinct between the twelfth and sixteenth centuries, most probably towards the latter. The main cause of its decline and extinction was probably hunting for its pelt, meat and castoreum, but habitat destruction may have been important in the loss of some small isolated populations.
Given that the causes of extinction of the Beaver in Scotland now no longer exist or can be effectively controlled, there is no reason why a feasibility study cannot proceed to assess the practicalities of a reintroduction.     

Low genetic polymorphism in the re-introduced Eurasian beaver (Castor fiber) population in Finland: implications for conservation

Mammal Research - Reduction of genetic diversity can lead to reduced fitness of species, such as the loss of adaptability to changing environments. The native Eurasian beaver (Castor fiber) was...     

The composition and properties of beaver (Castor fiber) meat

We analyzed the meat composition of ten females and seven males of sexually mature European beavers (Castor fiber L.). Cutting yield, percentage of particular elements, and chemical composition of the meat were determined. On average, a beaver carcass constitutes 48.6% of beaver body mass and contains 62.8% of meat, 14.5% of fat and 22.4% of bones. The thigh was found to be the largest and most valuable element constituting 33.4% of carcass weight and containing 66.7% of meat. Beaver meat has a high concentration of protein (20.9–21.8% wet wt.) and minerals (1.27–1.31%). The fat was characterized by a high proportion of polyunsaturated fatty acids (48.0–53.1%).     

Response of fish assemblages to water quality in boreal rivers

The relationship between fluvial fish assemblages and environmental variables including water quality was studied by nonmetric multidimensional scaling (NMS) and generalised regression neural network (GRNN). Fish assemblages in the studied boreal rivers in Central Finland showed a higher response to water quality than to other environmental variables such as altitude and river width. Of the water quality parameters, total phosphorus, oxygen saturation in winter and solids had the highest influence on fish assemblages. Brown trout (Salmo trutta L.) responded to water quality strongly by favouring pristine waters. Among other fish species, the responses were lighter, and the relative contribution of environmental variables varied. Percentage of fishless sites, i.e. no catch in electrofishing, was 4.4% when pH ≥ 6, and 38.2% when pH < 6. However, the most effective way to influence the fish assemblage composition, and to raise the fish-based FIFI integrity index value, would be to reduce loading of solids and phosphorus, rather than depressing acidification.     

The relative influence of catchment, riparian corridor, and reach-scale anthropogenic pressures on fish and macroinvertebrate assemblages in French rivers

This study compares the relative influences of physiography and anthropogenic pressures on river biota at catchment, riparian corridor, and reach scales. Environmental data, catchment and riparian corridor land use, anthropogenic modifications and biological data were compiled for 301 French sites sampled from 2005 to 2008. First, relationships between anthropogenic pressures and fish and macroinvertebrate assemblages were analysed using redundancy analysis. Second, the influences of physiography and the three scales of human pressures on biological assemblages were measured using variance partitioning. Distributions of fish and macroinvertebrate taxa along the pressure gradients agreed with bio-ecological knowledge. At the reach scale, assemblage variability among the 301 French sites was related to the presence of an impoundment and to poor water quality, while at larger scales it was linked to a gradient from forest to agricultural covers. In addition, a large proportion of the explained variability in assemblage composition was related to complex interactions among factors (~40%) and to physiographic variables (~30%). Furthermore, our results highlight that catchment land use better reflects local water quality impairments than hydromorphological degradations. Finally, this study supports the idea that human pressure effects on river communities are linked at several spatial scales and must be considered jointly.     

Development of nine new microsatellite loci for the American beaver, Castor canadensis (Rodentia: Castoridae), and cross-species amplification in the European beaver, Castor fiber

We developed nine new nuclear dinucleotide microsatellite loci for Castor canadensis. All loci were polymorphic, except for one. The number of alleles ranged from two to four and from five to 12 in populations from Arizona and Wisconsin, respectively. Average heterozygosity ranged from 0.13 to 0.86 per locus. Since cross-species amplification in Castor fiber was successful only in four loci, we tested also nine recently published C. canadensis loci in the Eurasian species. Eight of the published loci amplified; however, three were monomorphic. The number of alleles was lower in C. fiber than in C. canadensis at all loci tested.     

The influence of a planktivorous fish on zooplankton assemblages in experimental billabongs

This paper discusses the influence of predation by a planktivorous fish on zooplankton assemblages within experimental billabongs. Results suggest that the presence of a small planktivorous fish in experimental billabongs had only a small influence on the structure of zooplankton assemblages and densities of rotifers. Microcrustacean populations were dominated by juveniles, however there were greater numbers of juveniles when the planktivorous fish were present.     

The influence of coral reef benthic condition on associated fish assemblages

Accumulative disturbances can erode a coral reef's resilience, often leading to replacement of scleractinian corals by macroalgae or other non-coral organisms. These degraded reef systems have been mostly described based on changes in the composition of the reef benthos, and there is little understanding of how such changes are influenced by, and in turn influence, other components of the reef ecosystem. This study investigated the spatial variation in benthic communities on fringing reefs around the inner Seychelles islands. Specifically, relationships between benthic composition and the underlying substrata, as well as the associated fish assemblages were assessed. High variability in benthic composition was found among reefs, with a gradient from high coral cover (up to 58%) and high structural complexity to high macroalgae cover (up to 95%) and low structural complexity at the extremes. This gradient was associated with declining species richness of fishes, reduced diversity of fish functional groups, and lower abundance of corallivorous fishes. There were no reciprocal increases in herbivorous fish abundances, and relationships with other fish functional groups and total fish abundance were weak. Reefs grouping at the extremes of complex coral habitats or low-complexity macroalgal habitats displayed markedly different fish communities, with only two species of benthic invertebrate feeding fishes in greater abundance in the macroalgal habitat. These results have negative implications for the continuation of many coral reef ecosystem processes and services if more reefs shift to extreme degraded conditions dominated by macroalgae.