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1.
The location of Zebu, British, and Zebu x British cattle in tick-infested plots from March through September 1986 was compared with the location of Amblyomma americanum L. in the same plots. In April, May, and June, Zebu cattle spent less time (9.3-19.4%) in tick-infested quadrats than British (44.4-63.9%) or Zebu-British (49.0-69.3%) cattle. In the same months, the probability that A. americanum would contact Zebu cattle (1.5-19.6%) was significantly lower than for British (34.7-41.7%) or Zebu-British (30.2-56.9%) cattle. In April, May, June, and September, the probability that A. americanum detaching from cattle would drop into a quadrat presumed to be habitable for ticks was significantly lower for Zebu cattle (4.0-29.9%) than for British (64.9-72.6%) or Zebu-British (48.1-78.7%) cattle.  相似文献   

2.
Each of five adult and four juvenile coyotes (Canis latrans) was exposed to an oral dose of 50 Hepatozoon americanum oocysts recovered from Amblyomma maculatum ticks that previously fed on either naturally infected domestic dogs (Canis familiaris) or naturally infected wild coyotes. All coyotes exposed to H. americanum became infected, regardless of isolate source, and all exhibited mild to moderate clinical disease that simulated American canine hepatozoonosis in naturally infected dogs. At 100 days postexposure, parasitemia was greater in juvenile than adult coyotes (0.9% and 0.3%, respectively); radiographic imaging of femurs revealed moderate exostosis in all juveniles and mild to moderate new bone growth in four of five (80%) adult coyotes. Gross postmortem analysis of bone lesions demonstrated variation between age groups of coyotes but not between isolates of H. americanum. Microscopic evaluation of skeletal muscle revealed that parasite-induced lesions were significantly more numerous (t = 5.0, df = 7, P = 0.001) in juvenile than adult coyotes. Results of this study indicate that juvenile and adult coyotes are equally susceptible to experimental infection with H. americanum isolated from domestic dog and wild coyote sources. The age of coyotes at the time of exposure, and possibly the number of H. americanum oocysts ingested, might influence morbidity and mortality, but it appears that both adult and juvenile coyotes could be reservoirs of H. americanum.  相似文献   

3.
Twenty free-ranging coyotes (Canis latrans) in Oklahoma (USA) were examined for the presence of naturally occurring infections with Hepatozoon americanum and to determine if bone lesions attributable to H. americanum were present. Although eight of the 20 free-ranging coyotes were found to be naturally infected with H. americanum, no bone lesions were detected. In addition, two coyote pups were exposed to H. americanum oocysts collected from experimentally infected ticks and the course of the resulting infection was followed. Both experimentally infected coyotes developed hepatozoonosis detectable by specific muscle lesions beginning 4 wk after exposure. Bone lesions were detected grossly and histologically at necropsy. Histologic evidence of periosteal bone proliferation ranged from segmental areas of plump hypercellularity and thickening of the periosteum, with minor degrees of osteogenesis, to extensive proliferation of woven bone and periosteal hypercellularity and thickening. Nymphal Amblyomma maculatum that fed on one of the experimentally infected coyote pups became infected and mature H. americanum oocysts were recovered when the ticks molted to adults. These results demonstrate that coyotes in some parts of Oklahoma are naturally infected with H. americanum, that experimentally infected coyotes can develop clinical disease, including characteristic bone lesions, and that A. maculatum nymphs can acquire infections by feeding on them.  相似文献   

4.
This study examines the effects of burning and granivory on the reproductive success of the rare plant Amsinckia grandiflora (Boraginaceae). Fire is often used in California grasslands as a means of exotic species control, but the indirect effects these controls have on the reproductive ecology of native plants are rarely assessed. The interaction of fire with granivory of A. grandiflora seeds was examined in California grasslands over five years (1998–2002). In 1998 and 1999, both burned and unburned plots had bird-exclusion (netted) and no-exclusion (open) treatments. Predation rates were high (51–99%) and final predation rates did not differ among treatments. In 2000, granivory rates in the unburned, open plots were lower than in previous years (14%), and rodent trapping yielded only a single animal. Low granivory rates were observed in 2001 for unburned, open plots (47%). In 2001, burned/open plots experienced significantly more granivory (87%) than either burned/netted plots (37%) or unburned/open plots (47%). In 2002, every seed was taken from burned, open plots. Granivory was highly variable, ranging from 4 to 100% per plot over a 3-week period. Nearly all plots were discovered (>10% predation) by granivores in all trials in all years. When data from all treatments were combined, significant differences in granivory rates occurred among years, indicating stronger inter-year effects than within-year effects due to burning or bird exclusion. Fire affects granivory when overall predation rates are low, but when predation levels are high (as they were in 1998 and 1999), fire may not affect granivory occurring within the same year. Models extending seed survivorship through the dry summer indicate that most seeds are eaten, even when granivory rates are low.  相似文献   

5.
A new equine abortigenic disease, mare reproductive loss syndrome (MRLS), was recognized and significantly impacted the Ohio Valley in the springs of 2001 and 2002. MRLS caused approximately 330 million US dollars in losses in 2001. An epidemiological investigation of MRLS associated occurrence of the disease with exposure to eastern tent caterpillars (M. americanum). This work investigates the epidemiological association between M. americanum and MRLS to determine if this association was correlative or causative. A pilot study and simulated exposure to M. americanum and their excreta on pasture grasses. The pilot study advanced exposure of pregnant mares to M. americanum materials and 18 of the 29 mares in the study aborted with symptoms of MRLS before other cases were reported in the region. In, three of seven mares exposed to M. americanum aborted, while mares in control (n=6) and M. americanum frass (n=7) treatments had no losses. In, mares were fed frozen insect larvae in feed buckets mixed with oats. Abortions occurred in three of five mares receiving frozen M. americanum, while mares that were fed autoclaved M. americanum (n=5) or frozen gypsy moth larvae (n=4) had no abortions due to MRLS. In, M. americanum larvae were dissected and fractionated. Statistically significant numbers of abortions occurred only in the positive control group and in association with the M. americanum exoskeleton. All abortions induced by exposure to M. americanum exhibited changes in echogenicity of fetal fluids and bacteriological findings post abortion that were consistent with MRLS. These studies support the hypothesis that ingestion of M. americanum larvae induces the MRLS-type equine abortions, and provide experimental evidence that this lepidopteran larva can cause an abortigenic disease in a vertebrate host.  相似文献   

6.
Lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) is an important pest of sugarcane (a complex hybrid of Saccharum spp.) in southern Florida. Cultural controls for E. lignosellus were evaluated in preparation for the potential loss of effective insecticides. Field studies conducted in 2006 compared the effects of harvest residues from green-harvested sugarcane (no preharvest burning to remove leaf matter) on E. lignosellus stalk damage and yield. Damage by E. lignosellus was significantly lower in plant cane plots that were covered with harvest residues collected from a green-harvested field before shoot emergence compared with plots without harvest residue. There were no yield differences between plots with and without harvest residues in plant or ratoon sugarcane fields in the 2006 study. The effects of three postharvest tillage levels (conventional, intermediate, and no tillage) were evaluated in preharvest burned and green-harvested fields in 2008 and 2009. Significantly less E. lignosellus damage was observed in the green- versus preharvest burned fields in both years. Intermediate and no-tillage plots had very little damage in green-harvested field. Conventional tillage plots had the greatest damage in the green-harvested field and the lowest damage in the preharvest burned field. In 2008, biomass yield was greater in the intermediate than conventional tillage in the green-harvested field, but it was greater in the conventional than in other tillage levels in the preharvest burned field. These studies demonstrated that cultural controls could greatly reduce E. lignosellus damage in sugarcane without the use of insecticides.  相似文献   

7.
Amblyomma americanum (Linneaus) (Acari: Ixodidae), an important tick vector of human and animal disease, is not a competent vector of the bacterial agent of Lyme disease, Borrelia burgdorferi, although its range overlaps the geographical distribution of Lyme disease within the United States. A possible mechanism that could prevent acquisition of B. burgdorferi spirochetes from infected hosts is the toxic effect of A. americanum saliva on B. burgdorferi. The data presented here indicate that after 24 and 48 h of exposure to A. americanum saliva, significantly fewer B. burgdorferi were alive compared to treatment controls as assessed by spirochete motility under dark-field microscopy and resistance to the dead stain, propidium iodide. After 48 h, fewer than 13% of saliva-exposed B. burgdorferi were alive. In contrast, significantly more B. burgdorferi exposed to Ixodes scapularis (Acari: Ixodidae) saliva survived after 24 or 48 h compared to A. americanum saliva or treatment controls.  相似文献   

8.
Recent studies on aspergillosis in turkey poults   总被引:3,自引:0,他引:3  
A review of the studies on aspergillosis in turkey poults at the National Animal Disease Center include limited field studies, pathogenicity studies, and vaccine development. Natural ventilation in turkey rearing houses was effective in reducing airborne propagules of four major fungal genera, but the effectiveness of ventilation appeared to be limited by the width of the building. Aspergillus fumigatus was more effective than A. flavus in producing mortalities in aerosol exposed poults. Toxigenicity of A. flavus did not enhance its pathogenicity, and no apparent aflatoxin production occurred during pathogenesis in infected turkey poults. Spores of A. fumigatus were disseminated quite rapidly in poults exposed to aerosols, and alveolar macrophages from respiratory lavages taken immediately after exposure contained spores of A. fumigatus. Vaccines produced from germlings of A. fumigatus and administered to turkey poults were the most efficacious of five vaccines tested against challenge exposure to aerosols of A. fumigatus spores.  相似文献   

9.
Wildfires are a typical event in many Australian plant communities. Vesicular-arbuscular mycorrhizal (VAM) fungi are important for plant growth in many communities, especially on infertile soils, yet few studies have examined the impact of wildfire on the infectivity of VAM fungi. This study took the opportunity offered by a wildfire to compare the infectivity and abundance of spores of VAM fungi from: (i) pre-fire and post-fire sites, and (ii) post-fire burned and unburned sites. Pre-fire samples had been taken in May 1990 and mid-December 1990 as part of another study. A wildfire of moderate intensity burned the site in late December 1990. Post-fire samples were taken from burned and unburned areas immediately after the fire and 6 months after the fire. A bioassay was used to examine the infectivity of VAM fungi. The post-fire soil produced significantly less VAM infection than the pre-fire soil. However, no difference was observed between colonization of plant roots by VAM fungi in soil taken from post-fire burned and adjacent unburned plots. Soil samples taken 6 months after the fire produced significantly more VAM than corresponding soil samples taken one year earlier. Spore numbers were quantified be wet-sieving and decanting of 100-g, air-dried soil subsamples and microscopic examination. For the most abundant spore type, spore numbers were significantly lower immediately post-fire. However, no significant difference in spore numbers was observed between post-fire burned and unburned plots. Six months after the fire, spore numbers were the same as the corresponding samples taken 1 year earlier. All plants appearing in the burned site resprouted from underground organs. All post-fire plant species recorded to have mycorrhizal associations before the fire had the same associations after the fire, except for species of Conospermum (Proteaceae), which lacked internal vesicles in cortical cells in the post-fire samples.  相似文献   

10.
Glucose and methionine were malabsorbed in some intestinal regions of turkeys infected with Eimeria meleagrimitis, E. adenoeides, or E. dispersa. The decrease in absorption was not always related to the numbers of parasites in the cells or the extent of damage to the mucosa. With E. adenoeides, malabsorption was found in the jejunum even though parasites were not present. Conversely, with E. dispersa, no malabsorption was observed in the duodenum even though light microscopy showed numerous parasites. In many intestinal regions, damage to the mucosal surface visible with scanning electron microscopy (SEM) was slight or absent, although malabsorption was marked. No changes were noted with SEM in the structure and orientation of the brush border in these regions. Villar height was significantly reduced in the regions of heaviest infection when intestinal damage was visible. Conversely, the crypts of Lieberkühn were often two or three times as deep in infected poults as in uninfected poults. In general, no differences were found in the thickness of the circular and longitudinal muscle layers between the infected and uninfected poults. The dry weight of the intestinal tissue was less from infected poults than from uninoculated controls and was related to both region of the intestine and severity of the infection.  相似文献   

11.
Soil basidiomycetes play key roles in forest nutrient and carbon cycling processes, yet the diversity and structure of below ground basidiomycete communities remain poorly understood. Prescribed burning is a commonly used forest management practice and there is evidence that single fire events can have an impact on soil fungal communities but little is known about the effects of repeated prescribed burning. We have used internal transcribed spacer (ITS) terminal restriction fragment length polymorphism (T-RFLP) analysis to investigate the impacts of repeated prescribed burning every two or four years over a period of 30 years on soil basidiomycete communities in an Australian wet sclerophyll forest. Detrended correspondence analysis of ITS T-RFLP profiles separated basidiomycete communities in unburned control plots from those in burned plots, with those burned every two years being the most different from controls. Burning had no effect on basidiomycete species richness, thus these differences appear to be due to changes in community structure. Basidiomycete communities in the unburned control plots were vertically stratified in the upper 20 cm of soil, but no evidence was found for stratification in the burned plots, suggesting that repeated prescribed burning results in more uniform basidiomycete communities. Overall, the results demonstrate that repeated prescribed burning alters soil basidiomycete communities, with the effect being greater with more frequent burning.  相似文献   

12.
Natural wildfire regimes are important for ecosystem succession but can have negative ecological effects depending on fire characteristics. A portion of a granite rock barrens landscape that extends along the eastern shoreline of Georgian Bay, Lake Huron to eastern Ontario, Canada, burned in 2018 during a wildfire that affected >11,000 ha. This landscape is a biodiversity hotspot providing habitat for many species at risk where freshwater turtles nest in soil deposits in cracks and crevices in the bedrock dominated by moss (Polytrichum spp.) and lichen (Cladonia spp.) cover. To assess the initial effect of wildfire on freshwater turtle nesting habitat, we measured soil depths and estimated moss, lichen, and vascular plant cover at 2 morphology types (crevice, flat) in burned and unburned areas of the landscape. The probability that burned flat plots supported soil was near zero; the burned flat plots had 98% less soil volume compared to unburned flat plots. Although crevices were more resistant to soil loss, burned crevices still had a 15% lower probability of having soil and 35% less soil volume compared to unburned crevice plots. We estimated nest site availability by calculating the number of locations with shallow (5–10 cm), intermediate (10–20 cm), and deep (>20 cm) soils required for a small (5 cm × 5 cm) or medium (10 cm × 10 cm) nest chamber. Overall, the burned open rock barrens had 71–73% fewer sites with suitable soil depth and volume for a nest chamber of either size. Furthermore, burned plots had almost no lichen and moss cover but were dominated by bare soil, forbs, and jack pine (Pinus banksiana) seedlings. Although the loss of tree cover in previously forested areas may increase nest site availability for freshwater turtles in newly open areas, we suggest that organic soil combustion and soil erosion may require restoration activities in the post-fire landscape to support successful nesting of at-risk turtles. © 2020 The Wildlife Society.  相似文献   

13.
Numbers of total, metabolically active, dormant or dead axillarybuds, and growth characteristics were determined before andafter controlled burnings in Stipa tenuis Phil., a native foragegrass of the Caldén District in central Argentina. One-hectareplots were burned on 25 Mar. (Burn 1) or 4 Apr. 1991 (Burn 2),or remained unburned (control). Bud metabolic activity was examinedusing the tetrazolium test and the vital stain Evans' blue. Before fire, more than 83% of the axillary buds on previous-seasonstems of S. tenuis were metabolically active in all treatments.After fire, previous-season stems that produced tiller in thecontrol and Burn 2 plots had more than 75% of the axillary budsalive, but those that did not produce them had more than 82%of their axillary buds dead in the burned areas. This high budmortality was associated with direct fire effects on the fateof buds; most dead buds showed visible signs of dehydration.Since more than 97% of the plant stem bases did not producetillers after fire, tiller number per plant was reduced (P <0·05) in the burned plots to fewer than 22% of valuesof controls. Plant mortality was 50% higher at the Burn 1 thanat the Burn 2 site probably because the first site had a 43%lower soil moisture content (P < 0·05). At the endof the growing season, however, a different set of S. tenuisplants at both burned sites had a similar tiller number anddry weight to controls. These plants were probably in areasof lighter fuel loads and exposed to a less intense fire.Copyright1993, 1999 Academic Press Stipa tenuis Phil., thin needlegrass, controlled burning, bud viability, axillary meristems, regrowth  相似文献   

14.
在云南省大理市苍山火烧迹地采用陷阱法初步研究了火干扰对苍山云南松林步甲群落的影响.其中未火烧迹地步甲群落由7属14种组成;火烧迹地步甲群落由6属8种组成,样地同多度没有显著差异.未火烧迹地步甲群落物种组成不同于火烧迹地,但部分火烧迹地与未火烧迹地接近;健步甲Carabus solidior是森林生境良好的指示物种(IndVal=0.9489,P=0.001).研究显示,火干扰已经改变了云南松林步甲群落组成,降低了步甲群落的多样性.  相似文献   

15.
The effect of irradiation on the in vitro growth of Plasmodium falciparum was investigated. The cultured malarial parasites at selected stages of development were exposed to gamma rays and the sensitivity of each stage was determined. The stages most sensitive to irradiation were the ring forms and the early trophozoites; late trophozoites were relatively insensitive. The greatest resistance was shown when parasites were irradiated at a time of transition from the late trophozoite and schizont stages to young ring forms. The characteristics of radiosensitive variation in the parasite cycle resembled that of mammalian cells. Growth curves of parasites exposed to doses of irradiation upto 150 gray had the same slope as nonirradiated controls but parasites which were exposed to 200 gray exhibited a growth curve which was less steep than that for parasites in other groups. Less than 10 organisms survived from the 106 parasites exposed to this high dose of irradiation; the possibility exists of obtaining radiation-attenuated P. falciparum.  相似文献   

16.
The effects of fire recurrence on vegetation patterns in Quercus suber L. and Erica-Cistus communities in Mediterranean fire-prone ecosystems of south-eastern France were examined on stands belonging to 5 fire classes, corresponding to different numbers of fires (from 0 to 4) and time intervals between fires since 1959. A common pool of species was identified among the plots, which was typical of both open and closed maquis. Fire recurrence reduced the abundance of trees and herbs, whereas it increased the abundance of small shrubs. Richness differed significantly between the most contrasting classes of fire recurrence, with maximal values found in control plots and minimal values in plots that had burned recurrently and recently. Equitability indices did not vary significantly, in contrast to Shannon's diversity index which mostly correlated with richness. Forest ecosystems that have burnt once or twice in the last 50 years were resilient; that is to say they recovered a biomass and composition similar to that of the pre-fire state. However, after more than 3-4 fires, shrubland communities displayed lower species richness and diversity indices than unburned plots. The time since the last fire and the number of fires were the most explanatory fire variables, governing the structure of post-fire plant communities. However, environmental factors, such as slope or exposure, also made a significant contribution. Higher rates of fire recurrence can affect the persistence or expansion of shrublands in the future, as observed in other Mediterranean areas.  相似文献   

17.
Six hundred sixty-five hunter-killed white-tailed deer (Odocoileus virginianus) from 18 counties in Alabama (USA) were examined for ticks. Most of the collections were made at state-operated wildlife management areas. Four species of ticks (n = 4,527) were recovered: the lone star tick Amblyomma americanum (n = 482); the Gulf Coast tick A. maculatum (n = 11); the winter tick Dermacentor albipictus (n = 1,242); and the black-legged tick Ixodes scapularis (n = 2,792). Fifty-six percent of the ticks (n = 2,555) were examined for Borrelia sp. spirochetes using an immunofluorescent, polyclonal antibody assay. Spirochetes were detected in I. scapularis (five females, seven males) from Barbour, Butler, Coosa, and Lee counties and A. americanum (four males, four nymphs) from Hale, Lee, and Wilcox counties. Area-specific prevalences in ticks were as high as 3.3% for I. scapularis and 3.8% for A. americanum.  相似文献   

18.
Fire has become an increasingly important disturbance event in south-western Amazonia. We conducted the first assessment of the ecological impacts of these wildfires in 2008, sampling forest structure and biodiversity along twelve 500 m transects in the Chico Mendes Extractive Reserve, Acre, Brazil. Six transects were placed in unburned forests and six were in forests that burned during a series of forest fires that occurred from August to October 2005. Normalized Burn Ratio (NBR) calculations, based on Landsat reflectance data, indicate that all transects were similar prior to the fires. We sampled understorey and canopy vegetation, birds using both mist nets and point counts, coprophagous dung beetles and the leaf-litter ant fauna. Fire had limited influence upon either faunal or floral species richness or community structure responses, and stems <10 cm DBH were the only group to show highly significant (p = 0.001) community turnover in burned forests. Mean aboveground live biomass was statistically indistinguishable in the unburned and burned plots, although there was a significant increase in the total abundance of dead stems in burned plots. Comparisons with previous studies suggest that wildfires had much less effect upon forest structure and biodiversity in these south-western Amazonian forests than in central and eastern Amazonia, where most fire research has been undertaken to date. We discuss potential reasons for the apparent greater resilience of our study plots to wildfire, examining the role of fire intensity, bamboo dominance, background rates of disturbance, landscape and soil conditions.  相似文献   

19.
Early post-hatch fasting induces satellite cell self-renewal   总被引:3,自引:0,他引:3  
Early post-hatch satellite cell kinetics are an important aspect of muscle development, and understanding the interplay between fasting and muscle development will lead to improvements in muscle mass following an illness, and optimal meat production. The objective of this experiment was to test the influence of immediate post-hatch fasting on satellite cells in the poult. Male Nicholas poults (Meleagris gallopavo) were placed into two treatments: a fed treatment with immediate access to feed and water upon placement and a fasted treatment without access to feed and water for the first three days post-hatch. 5-bromo-2'-deoxyuridine (BrdU) was injected intra-abdominally in all poults to label mitotically active satellite cells. The pectoralis thoracicus muscle was harvested two hours following the BrdU injection. Immunohistochemistry for BrdU, Pax7, Bcl-2, Pax7 with BrdU, and determining myofiber cross-sectional area along with computer-based image analysis was used to study muscle development. Fed poults had higher body masses throughout the experiment (P< or =0.01), and they had higher pectoralis thoracicus muscle mass (P< or =0.01) at ten days of age than the fasted poults. Fed poults had higher satellite cell mitotic activity at three days and four days of age (P< or =0.01) compared to the fasted poults. However, Pax7 labeling index was higher in the fasted poults (P< or =0.01) at three days, four days, and five days post-hatch than the fed group. Similarly Bcl-2 labeling was higher in the fasted than in the fed group at three days post-hatch. Therefore, fasting depleted proliferating satellite cells indicated by the lower BrdU labeling in the fasted poults compared to the fed poults, and conserved the satellite cell proliferative reserve indicated by the higher level of Pax7 labeling for the fasted poults compared to the fed poults.  相似文献   

20.
We examined long‐term responses of an Amazonian bird assemblage to wildfire disturbance, investigating how understory birds reacted to forest regeneration 1, 3, and 10 years after a widespread fire event. The bird community was sampled along the Arapiuns and Maró river catchments in central Brazilian Amazonia. Sampling took place in 1998, 2000, and 2008 using mist‐nets in eight plots (four burned, four unburned sites). Species richness did not change significantly in unburned sites. In burned sites, however, we found significantly lower richness in 1998, higher richness in 2000, and similar richness in 2008. Multi‐dimensional scaling ordination showed consistent differences in bird communities both within burned sites sampled in different sampling years, and between burned and unburned sites in all years. Of the 30 most abundant species, 12 had not recovered 10 years after the fires, including habitat specialists such as mixed flocks specialists and ant‐followers. Fire‐disturbance favored three species (two hummingbirds and a manakin) in the short term only. All other species were either favored throughout the study (seven species of omnivores and small insectivores) or did not show a clear response (eight species). In burned sites, we also found significantly lower abundance of species sensitive to disturbances and habitat specialists over the entire study period. Although the bird community seems to be recovering in terms of richness, the overall community composition and abundance of some species in post‐burned and unburned sites remain very different, and have not recovered after 10 years of forest regeneration.  相似文献   

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