Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna

Mutualisms are key components of biodiversity and ecosystem function, yet the forces maintaining them are poorly understood. We investigated the effects of removing large mammals on an ant-Acacia mutualism in an African savanna. Ten years of large-herbivore exclusion reduced the nectar and housing provided by plants to ants, increasing antagonistic behavior by a mutualistic ant associate and shifting competitive dominance within the plant-ant community from this nectar-dependent mutualist to an antagonistic species that does not depend on plant rewards. Trees occupied by this antagonist suffered increased attack by stem-boring beetles, grew more slowly, and experienced doubled mortality relative to trees occupied by the mutualistic ant. These results show that large mammals maintain cooperation within a widespread symbiosis and suggest complex cascading effects of megafaunal extinction.     

Fatal Clostridium botulinum toxicosis in eleven Holstein cattle fed round bale barley haylage.

Twenty-two lactating Holstein cattle in Tennessee had clinical signs of intoxication with preformed Clostridium botulinum toxin. These signs included weakness, paralysis of the tongue and chest muscles, abdominal breathing, and, in 11 of the 22 cows, death. Differential diagnoses included hypocalcemia, hypomagnesemia, carbohydrate overload, and several toxicoses including mycotoxin, lead, nitrate, organophosphate, atropine or atropine-like alkaloid, and botulism. A diagnosis of botulism by the ingestion of preformed C. botulinum type B toxin was made by eliminating these other diseases, by finding C. botulinum type B spores in 3 bales of round bale barley haylage fed to these cattle, and by isolating preformed type B toxin from 1 of the 3 bales. Confirmation of the toxin type was made by demonstrating mouse lethality by intraperitoneal injection of specimen extracts with neutralization by C. botulinum type B antitoxin. The haylage, harvested green and encased in black plastic bags to facilitate fermentation, was presumably contaminated by the botulinum toxin when fermentation failed to produce enough acid to lower the pH to 4.5, the pH below which C. botulinum growth is inhibited. Farmers and ranchers who use round hay balers to produce haylage should be alert to this potential problem.     

An IgG-binding protein A homolog in Staphylococcus hyicus

Shotgun phage display was used to identify a homolog of the IgG-binding protein staphylococcal protein A in Staphylococcus hyicus type strain CCUG 15602/ATCC 11249. This bacterium is the causative agent of exudative epidermitis in pigs and can also cause mastitis in cattle. A protein with similar features as the originally identified protein A in Staphylococcus aureus was described; an YSIRK-type signal peptide, four IgG-binding domains, a putative peptidoglycan-binding domain, and a cell wall anchoring motif (LPXTG) was present. The highest degree of similarity was to a protein A homolog in Staphylococcus pseudintermedius. However, typical Xr polypeptide repeats present in the protein A of S. aureus and S. pseudintermedius could not be identified in the protein A of S. hyicus. The presence of the spa gene in ten porcine and eight bovine clinical isolates of S. hyicus was investigated by PCR. In all isolates, the spa gene could be detected but the amplicons were of two sizes. Sequence analysis of four selected PCR amplicons showed that only three IgG-binding domains were present in the protein A of clinical isolates generating a smaller spa fragment. The finding of spa in S. hyicus contributes to an increased understanding of potential virulence factors in this species.     

Effect of frusemide on transvascular fluid fluxes across the lung in exercising horses

Reasons for performing study: Frusemide (Fru) is widely prescribed for management of racehorses experiencing EIPH. The effect of Fru in the lung appears to be a reduction in transcapillary pressures and inhibition of the erythrocyte anion exchange, which may lead to attenuation of transpulmonary fluid fluxes during exercise. Hypothesis: Treatment with Fru will attenuate transpulmonary fluid fluxes in horses during high intensity exercise. Methods: In a crossover study, 6 race‐fit Standardbred horses were treated with 250 mg of Fru i.v. (FruTr) or placebo (Con) 4 h before exercise on a high speed treadmill until fatigue. Arterial and central mixed venous blood, as well as CO₂ elimination and O₂ uptake, were sampled. Volume changes across the lung and transvascular fluid fluxes were calculated from changes in haemoglobin, packed cell volume, plasma protein and cardiac output (Q). Results: During exercise, Q increased in both Con and FruTr, with Q being significantly lower in FruTr (mean ± s.e. 301.8 ± 8.5 l/min at fatigue) compared to Con (336.5 ± 15.6 l/min) (P<0.01). At rest frusemide had no effect on erythrocyte (J_ER) and transvascular (J_V‐A) fluid fluxes across the lung. Exercise had a significant effect on J_ER and J_V‐A (P≤0.02). During exercise, J_ER (at fatigue 14.6 ± 2.3 l/min and 11.6 ± 2.2 l/min in Con and FruTr, respectively) and J_V‐A (at fatigue14.9 ± 2.3 l/min and 12.0 ± 2.2 l/min in Con and FruTr, respectively) were not significantly different between Con and FruTr (P = 0.6 and P = 0.8 for J_ER and J_V‐A, respectively). Conclusions and clinical importance: Fru does not have a measurable effect on J_ER and J_V‐A. Cardiac output was reduced in FruTr, suggesting that there were also smaller changes in the capillary recruitment and transvascular transmural hydrostatic pressures; however, this did not effect J_V‐A. Therefore, Fru at the dose of 250 mg does not appear to be an effective treatment for regulating pulmonary transvascular forces during exercise in horses.     

Aflatoxin and fumonisin contamination of commercial corn (Zea mays) hybrids in Mississippi

Resistance to mycotoxin contamination was compared in field samples harvested from 45 commercial corn (maize) hybrids and 5 single-cross aflatoxin-resistant germplasm lines in years with high and moderate heat stress. In high heat stress, mycotoxin levels were (4.34 +/- 0.32) x 10(3) microg/kg [(0.95-10.5 x 10(3) microg/kg] aflatoxins and 11.2 +/- 1.2 mg/kg (0-35 mg/kg) fumonisins in commercial hybrids and 370 +/- 88 microg/kg (140-609 microg/kg) aflatoxins and 4.0 +/- 1.3 mg/kg (1.7-7.8 mg/kg) fumonisins in aflatoxin-resistant germplasm lines. Deoxynivalenol was detected (one-fourth of the samples, 0-1.5 mg/kg), but not zearalenone. In moderate heat stress, mycotoxin levels were 6.2 +/- 1.6 microg/kg (0-30.4 microg/kg) aflatoxins and 2.5 +/- 0.2 mg/kg (0.5-4.8 mg/kg) fumonisins in commercial hybrids and 1.6 +/- 0.7 microg/kg (0-7 microg/kg) aflatoxins and 1.2 +/- 0.2 mg/kg (0.5-3.0 mg/kg) fumonisins in aflatoxin-resistant germplasm lines. The results are consistent with heat stress playing an important role in the susceptibility of corn to both aflatoxin and fumonisin contamination, with significant reductions of both aflatoxins and fumonisins in aflatoxin-resistant germplasm lines.     

A geostatistical method to account for the number of aliquots in composite samples for normal and lognormal random variables

Geostatistical methods can be used to calculate predictions of soil variables at unsampled locations, but the methodology is typically based on samples collected on identical sample supports. In this paper, we provide and test theory that allows the inclusion of data from mixed sample supports in a single analysis. In particular, we consider composite sample supports that are defined by the number of aliquots used to form a single composite sample, n_i, and the set of locations, x _i, from which the aliquots were collected. We allow both n_i and x _i to vary between samples ( x _i can vary in the extent and geometry of the aliquot locations), and thereby show how point data (a special case of composite data, defined by n_i = 1 and x _i as the known sample point) can be included in the same geostatistical analysis as composite data. A further complication arises when data are not normally distributed, rather their logarithm is. When composite sampling is used for such lognormal data, the sample support affects not only the variance but also the mean. We give the theory for normally distributed variables, and also derive an approximation that can be used when the point‐support variable is lognormal. We focus on this latter case, and test the approach with a series of simulation experiments. Finally, we illustrate the approach on a dataset of soil organic carbon (SOC) values from a grazing property in Queensland, Australia, where soil information from two measurement phases was obtained on different supports.     

Comparison of the effect of storage environment on tuber contamination withErwinia carotovora

Summary One tonne boxes of seed potatoes cv. Désirée contaminated withErwinia carotovora were held in four different types of farm stores. In general, contamination fell rapidly immediately after harvest and rose later in the storage season. The extent of these changes varied considerably with store type. The greatest reduction was from a log count of 5.5 to 2.1 after one month storage, followed by a rise to 5.1 prior to planting. No relationship was found between store temperature, relative humidity and change in contamination. There was some evidence that reduction in contamination was related to duration of ventilation, and rise in contamination to onset of sprouting. A sample held at a constant 4°C showed little reduction in contamination, and no rise occurred later in the storage season.