Variation in reproductive mode across the latitudinal range of invasive Russian knapweed

For invading species, reproduction is a critical determinant of population establishment as well as spread into new areas. When species have multiple modes of reproduction, the prevalence of different modes can influence management decisions. We used genetic markers to determine the prevalent method of recruitment for invasive Russian knapweed (Acroptilon repens). This species forms patches and can spread by both rhizomic growth and seed from outcrossing. We found no shared genotypes between 41 western North American populations, indicating at the macroscale, Russian knapweed is spreading via seed to distant locations. We also examined drivers of reproductive mode by comparing clonality with large-scale environmental factors across the invasion. We found a correlation between latitude and clonal versus seed reproduction, with clonality higher in northern latitude populations. This trend was associated most parsimoniously with decreasing maximum annual temperature and 30-year average of available growing degree days, and increasing soil organic carbon content. These results have management implications: if not properly temporally implemented, grazing or herbicide applications that create open spaces for recruitment may increase the likelihood of Russian knapweed patch persistence through seed, and recently released galling biological control agents in North America may be less effective in northern latitudes where Russian knapweed spread by seed is less prevalent.

The effects of agent hybridization on the efficacy of biological control of tansy ragwort at high elevations

The success rate of weed biological control programs is difficult to evaluate and the factors affecting it remain poorly understood. One aspect which is still unclear is whether releases of multiple, genetically distinct populations of a biological control agent increase the likelihood of success, either by independent colonization of different environmental niches or by hybridization that may increase the agent's fitness and adaptive ability. Since hybridization is often invoked to explain the success of unintentionally introduced exotic species, hybridization among biocontrol agents may be similarly important in shaping the effectiveness of biological control programs. In this study, we first evaluated intraspecific hybridization among populations of a weed biological control agent, the ragwort flea beetle, Longitarsus jacobaeae. These insects were introduced as part of a classical biological control program from Italy and Switzerland. We genotyped 204 individuals from 15 field sites collected in northwest Montana, and an additional 52 individuals that served as references for Italian and Swiss populations. Bayesian analysis of population structure assigned seven populations as pure Swiss and one population as pure Italian, while intraspecific hybrid individuals were detected in seven populations at frequencies of 5%-69%. Subsequently, we conducted a 2-year exclusion experiment using six sites with Swiss beetles and three with hybrid beetles to evaluate the impact of biological control. We found that biological control by Swiss beetles and by hybrid beetles is effective, increasing mortality of the target plant, Jacobaea vulgaris, by 42% and 45%, and reducing fecundity of surviving plants by 44% and 72%, respectively. Beetle densities were higher and mortality of larger plants was higher at sites with hybrids present. These results suggest that hybridization of ragwort flea beetles at high-elevation sites may improve biological control of tansy ragwort and that intraspecific hybridization of agents could benefit biological control programs.

Elevational distribution of mosquitoes in a mountainous area of southeastern Wyoming

During the summer of 1984, mosquito sampling with CDC miniature light traps and standard mosquito dippers was used to investigate the elevational distribution of different species of mosquitoes. Of 27 species found in significant numbers in the study area in southeastern Wyoming, 8 were found primarily in the lower elevations (2,134 and 2,591 m). Nine additional species were found in both the middle and lower elevations (2,134-3,048 m), whereas 8 occurred only in the middle areas (2,592-3,048 m). A single species (Aedes punctor) was found in both the middle and upper elevations (2,439-3,292 m), and yet another species (Aedes impiger) was found primarily in the upper (alpine) area, from 3,049, to 3,292 m. There is some evidence to indicate that restriction in elevational distribution is a result of habitat specificity.

Testicular circulatory isolation in man: comparison of radionuclide angiography with Doppler evaluation

Testicular circulatory isolation (TCI) holds promise as a method to avoid drug-induced infertility in male patients about to receive cancer chemotherapy. Complete exclusion of blood flow to the testicle is essential to the success of this technique. We have compared the hand-held Doppler probe and radionuclide angiography (technetium-99m pertechnetate) as monitors of testicular blood flow in 10 patients subjected to unilateral TCI. When Doppler evaluation indicated that testicular circulation had been interrupted, the radionuclide angiogram uniformly confirmed and quantified this conclusion. These results validate the hand-held Doppler as an appropriate tool for assessing testicular blood flow in patients undergoing TCI.

Work force problems in nuclear medicine and possible solutions

Nuclear medicine practice and work force demographics reflect the historically diverse evolution of this specialty. The most pressing problem for nuclear medicine is a projected shortage of fully trained physicians due to practitioner retirement that is unmatched by residency program output. During the past decade the number of 2-year nuclear medicine residency programs (average of 90) and the total number of residents (average of 191 in both years) have remained remarkably stable. In contrast, the number of 1-year nuclear radiology residency programs, available positions, and residents have declined significantly. A similar decline is seen in radiologists obtaining full nuclear medicine training and American Board of Nuclear Medicine (ABNM) board certification. This void has been filled by nonradiologist trainees who only seek certification by ABNM. Perhaps such shifts in resident profile are an early indicator that the United States is evolving toward practice models in which nuclear medicine is provided by fully trained, full-time physicians, similar to the European work force model. The recent Society of Nuclear Medicine survey of 10,446 physicians who practice nuclear medicine shows a current practice pattern in the United States that is distinctly different from that in Europe. The vast majority of those surveyed practice part time. Only 7% of all physicians who practice nuclear medicine do so full time, (ie more than 90% of the time), but they account for as much full-time employee (FTE) work load as 70% of all part-time physicians. Although the number of radiologists entering nuclear medicine is declining, 51% of total FTE work load is still done by radiologists with only American Board of Radiology certification. Physicians certified by ABNM represent 42% of all FTE work load. Cardiologists certified by American Board of Internal Medicine-Cardiovascular Specialization account for approximately 4% of nuclear medicine (15% of total cardiovascular nuclear medicine) FTE work load. Work force shortage of nuclear medicine technologists remains a chronic problem in spite of extensive study: however, recent predictions suggest some improvement in the future. Solutions to work force problems facing nuclear medicine will require ongoing data surveys, aggressive recruitment of trainees, expansion of training positions, and socioeconomic initiatives that promote desirable future practice models.

Acute cerebral infarction in monkeys: an experimental study using MR imaging

Magnetic resonance (MR) imaging was performed in five monkeys with experimentally induced acute cerebral infarction to define the MR imaging features and correlate these with computed tomographic (CT) findings, laboratory analysis, and histopathologic studies. Acute infarct (2-4 hours after embolization) was generally visible on MR images but not on CT scans. CT at 24 and 48 hours did show the infarcts. In all cases the infarct was more clearly depicted with MR imaging and was visualized as an area of high signal intensity on T2-weighted images. Spectrometric nuclear MR measurements of the postmortem cerebral tissue confirmed prolongation of both T1 and T2 values similar to that calculated from MR images. At postmortem laboratory testing, the area of infarction detected with MR imaging had decreased specific gravity and increased water content, reflecting edema.

Tc-99m hydroxymethylene diphosphonate and Tc-99m methylene diphosphonate: biological and clinical comparison: concise communication

The biologic and imaging characteristics of Tc-99m HMDP and Tc-99m MDP were compared in ten patients. Tc-99m HMDP blood levels were marginally lower at 4 hr. There were no significant differences in 4-hr urinary clearance, normal bone-to-background ratio, or ratio of lesion to normal bone. Relative image quality comparison showed a slight preference for Tc-99m HMDP. Biologically Tc-99m HMDP compares favorably with Tc-99m MDP. Under the conditions of this study, Tc-99m HMDP image quality is at least comparable to that of Tc-99m MDP.