Pet food safety: sodium in pet foods

Healthy dogs and cats appear to be able to adjust to differing amounts of sodium in their diet via the rennin-angiotensin-aldosterone mechanisms. There is no strong evidence that increased dietary sodium increases the risk of hypertension in dogs and cats, and the current recommendation for hypertensive animals is to avoid high dietary salt intake without making a specific effort to restrict it. The prevalence of salt sensitivity and its effect on blood pressure has not been determined for cats or dogs. The ideal amount of sodium in the diet of dogs and cats with cardiac deficiency has not been determined, as increasing may detrimentally increase the extracellular fluid volume, but decreasing it may detrimentally increase the activation of the rennin-angiotensin-aldosterone system. Increased dietary sodium increases urine output and may decrease the risk of forming calcium oxalate uroliths due to the decrease in relative supersaturation of solutes. However, caution should be used in increasing the sodium intake of patients with renal disease as increased dietary sodium may have a negative effect on the kidneys independent of any effect on blood pressure.     

Landscape genetics of the foundational salt marsh plant species black needlerush (<Emphasis Type="Italic">Juncus roemerianus</Emphasis> Scheele) across the northeastern Gulf of Mexico

Context

Common species important for ecosystem restoration stand to lose as much genetic diversity from anthropogenic habitat fragmentation and climate change as rare species, but are rarely studied. Salt marshes, valuable ecosystems in widespread decline due to human development, are dominated by the foundational plant species black needlerush (Juncus roemerianus Scheele) in the northeastern Gulf of Mexico.

Objectives

We assessed genetic patterns in J. roemerianus by measuring genetic and genotypic diversity, and characterizing population structure. We examined population connectivity by delineating possible dispersal corridors, and identified landscape factors influencing population connectivity.

Methods

A panel of 19 microsatellite markers was used to genotype 576 samples from ten sites across the northeastern Gulf of Mexico from the Grand Bay National Estuarine Research Reserve (NERR) to the Apalachicola NERR. Genetic distances (F_ST and D_ch) were used in a least cost transect analysis (LCTA) within a hierarchical model selection framework.

Results

Genetic and genotypic diversity results were higher than expected based on life history literature, and samples structured into two large, admixed genetic clusters across the study area, indicating sexual reproduction may not be as rare as predicted in this clonal macrophyte. Digitized coastal transects buffered by 500 m may represent possible dispersal corridors, and developed land may significantly impede population connectivity in J. roemerianus.

Conclusions

Results have important implications for coastal restoration and management that seek to preserve adaptive potential by sustaining natural levels of genetic diversity and conserving population connectivity. Our methodology could be applied to other common, widespread and understudied species.

     

Estimating the spatial scales of landscape effects on abundance

Context

Spatial variation in abundance is influenced by local- and landscape-level environmental variables, but modeling landscape effects is challenging because the spatial scales of the relationships are unknown. Current approaches involve buffering survey locations with polygons of various sizes and using model selection to identify the best scale. The buffering approach does not acknowledge that the influence of surrounding landscape features should diminish with distance, and it does not yield an estimate of the unknown scale parameters.

Objectives

The purpose of this paper is to present an approach that allows for statistical inference about the scales at which landscape variables affect abundance.

Methods

Our method uses smoothing kernels to average landscape variables around focal sites and uses maximum likelihood to estimate the scale parameters of the kernels and the effects of the smoothed variables on abundance. We assessed model performance using a simulation study and an avian point count dataset.

Results

The simulation study demonstrated that estimators are unbiased and produce correct confidence interval coverage except in the rare case in which there is little spatial autocorrelation in the landscape variable. Canada warbler abundance was more highly correlated with site-level measures of NDVI than landscape-level NDVI, but the reverse was true for elevation. Canada warbler abundance was highest when elevation in the surrounding landscape, defined by an estimated Gaussian kernel, was between 1300 and 1400 m.

Conclusions

Our method provides a rigorous way of formally estimating the scales at which landscape variables affect abundance, and it can be embedded within most classes of statistical models.

     

Cytogenetic mechanism for reversion of triploids to heteroploid mosaics in Crassostrea gigas (Thunberg) and Crassostrea ariakensis

Triploid oyster induction has been very successful. However, during field culture, a certain proportion of triploids apparently loses one set of chromosomes, ‘reverting’ to diploid–triploid mosaics. The revertants will lose their aquaculture advantages due to the recovery of reproductive ability. Mitotic chromosomes were observed in mosaics of Crassostrea gigas and Crassostrea Ariakensis to elucidate the cytogenetic mechanism of reversion. Most individuals showed a modal number of 30 in triploid cells and varying numbers of chromosomes in other cells. From all 15 mosaics of C. gigas and 16 mosaics of C. ariakensis individuals, high proportions of aneuploid cells with various numbers of chromosomes were observed. Most of the aneuploid cells were hypotriploid cells with 26–29 chromosomes. Notably, in 10 out of 15 C. gigas and 9 out of 16 C. ariakensis, some cells consisted of 20–26 well‐spread chromosomes and 3–10 chromosome ‘clumps’. Individuals with more chromosome clumps tended to have higher percentages of hypotriploid cells. The correlation between these two categories of cells was significant (P<0.05) in C. gigas and highly significant (P<0.01) in C. ariakensis. Thus, we conclude that some chromosomes are eliminated during mitotic divisions because they clump together and are thus unable to undergo normal segregation.     

Effects of management regime on the abundance and nest survival of shrubland birds in wildlife openings in northern New England, USA

Many shrubland bird species are declining in eastern North America and as a result forest managers have used a variety of techniques to provide breeding habitat for these species. The maintenance of permanent “wildlife openings” using prescribed burns or mechanical treatments is a widely used approach for providing habitat for these species, but there have been no studies of the effects of treatment regime on bird abundance and nest survival in managed wildlife openings. We studied shrubland birds in wildlife openings on the White Mountain National Forest (WMNF) in New Hampshire and Maine, USA, during 2003 and 2004. We analyzed bird abundance and nest survival in relation to treatment type (burned versus mowed), treatment frequency, time since treatment, and patch area. We found that wildlife openings provided habitat for shrubland birds that are not present in mature forest. There was relatively modest support for models of focal bird species abundance as a function of treatment regime variables, despite pronounced effects of treatment on habitat conditions. This probably was attributable to the combined effects of complex site histories and bird site fidelity. Overall nest success (52%) was comparable to other types of early-successional habitats in the region, but there were few supported relationships between nest survival and treatment variables. We conclude that wildlife openings provide quality habitat for shrubland birds of high conservation interest as long as managers ensure treatment intervals are long enough to permit the development of woody vegetation characteristic of the later stages of this sere. Also, wildlife openings should be large enough to accommodate the territory sizes of all target species, which was ≥1.2 ha in this study.     

Evaluation of type I fusarium head blight resistance of wheat using non-deoxynivalenol-producing fungi

A series of experiments was conducted to determine whether type I resistance (resistance to initial infection) to fusarium head blight (FHB) in wheat could be assessed using fungal species/isolates that do not produce deoxynivalenol (DON), a mycotoxin critical to the spread of Fusarium graminearum in the wheat spike. It was shown that, while the non-toxin-producing species Microdochium nivale and M. majus could infect following spray inoculation of wheat spikes, they were unable to spread within the spike following point inoculation. However, although these species might reveal type I resistance, they are not highly pathogenic towards wheat. A nivalenol (NIV)-producing isolate of F. graminearum caused high levels of disease following spray inoculation, but spread only very slowly within the spike and rarely induced bleaching above the point of inoculation. It is proposed that spray inoculation with an appropriate, aggressive, non-DON-producing FHB pathogen may be used to characterize type I resistance to complement point inoculation with a DON-producing isolate to assess type II resistance (resistance to spread within the spike).     

Somatic hybridization of high yield,cold-hardy and disease resistant parents for citrus rootstock improvement

Summary

Increasing losses of trees to diseases, expansion of plantings into more marginal production areas and the need to control tree size to reduce harvesting costs have elevated the demand for new improved citrus rootstocks in Florida. A major strategy of the CREC rootstock improvement programme has been to use protoplast fusion to produce allotetraploid somatic hybrids that combine complementary rootstock germplasm. Tetraploid citrus rootstocks have been shown to have a built-in tree size control component due to polyploidy. This report focuses on the incorporation of newly identified superior rootstock germplasm into the somatic hybridization programme. Poncirus trifoliata 50–7, a selection of trifoliate orange selected for superior resistance to Phytophthora nicotianae, was hybridized with sour orange, Changsha mandarin, Navel orange, and a seedy white ‘Duncan’ type grapefruit. High-yielding Benton citrange (Citrus sinensis 3 Poncirus trifoliata) was hybridized with Changsha mandarin and sour orange. More than 200 plants of each of these six new somatic hybrids were propagated via tissue culture and rooted cuttings. To assess their horticultural performance, all the somatic hybrids were budded with commercially important scions and planted in replicated trials representing the two most important soil types in Florida. Seed trees of each somatic hybrid have also been planted in the field to determine fruiting potential and level of polyembryony.