Epidemiology of neoplasia in captive black-footed ferrets (Mustela nigripes), 1986-1996.

The epidemiology of neoplastic disease was studied retrospectively in the captive population of black-footed ferrets (Mustela nigripes). Postmortem reports were reviewed and archived tissues examined from 184 of the 227 adult (>1 yr old) black-footed ferrets that died from the beginning of the current captive propagation program in late 1985 to the end of 1996. A total of 185 neoplasms, of 28 distinct phenotypes, were seen in 102 (55.4%) of these ferrets. There was more than one tumor type present in 51 ferrets. Tumors of the apocrine glands (28.3%), renal tubular neoplasms (20.7%), and biliary cystadenoma or carcinoma (20.1%) were the most common neoplasms. The probability of developing most types of neoplasms increased with age. Neoplasms of the apocrine glands were more common in males and may be hormonally influenced. The unusually high prevalence of biliary cystadenocarcinoma may be secondary to the common occurrence of intrahepatic biliary cysts in this population. Although neoplasia is an important cause of mortality in captive adult black-footed ferrets, its impact on captive propagation of the species, and on the wild population, is probably limited because clinically significant tumors are encountered almost exclusively in postreproductive ferrets (>3 yr old) and because ferrets released into their natural habitat rarely reach susceptible age.     

Genetic variation in bitter pit and fruit calcium concentrations within a diverse apple germplasm collection

Summary Genetic variability in the apple [Malus] fruit disorder bitter pit and fruit calcium concentrations ([Ca]) was determined in 25 seedling families at each of two sites from 1999 to 2000 and again for one site, in 2001. Most trees were free of pit or had low pit incidence, which could be approximated by an over-dispersed binomial distribution. A genetic component to external and internal pit incidence was found across both sites and all years. This effect was irrespective of the use of several cropping factors, average fruit weight or fruit mineral concentrations as covariates in the analyses. Year and/or site always had substantial effects on pit incidence. Interactions of genetic effects with site or year were also detected with large differences in mean pit incidence between sites or years for some families but not others. No relationship was found between mean family pit incidence and mean family [Ca] or mean family harvest date. However fruit [Ca] and harvest date were usually important predictors of within-family variation in pit incidence. For any one seedling, family had the largest effect on bitter pit incidence followed by site and [Ca] and the smallest effect was that of harvest date. [Ca] showed a strong genetic component and estimated family means of [Ca] were consistent at different sites and years. These results suggest that susceptibility of apple genotypes to bitter pit in breeding programmes may be best assessed through screening across multiple sites and seasons. Fruit [Ca] might be useful as an indirect selection index for bitter pit within, but not among families.     

Evaluating the utility of Arabidopsis thaliana as a model for understanding heterosis in hybrid crops

Despite the phenomenon of heterosis having been used to improve crop productivity for almost a century, there is little understanding of the molecular mechanisms involved. Heterosis has been described recently in the widely used plant model Arabidopsis thaliana. To assess the opportunity afforded by this system, we have developed, through pollination to a male sterile female parent (Ler ms1), a range of hybrids of A. thaliana accessions. We tested this method of hybrid production in A. thaliana by comparing seed produced by natural pollination and hand pollination of emasculated plants. Our results demonstrate that using male sterile lines, which more closely represent methods used for hybrid crop production, circumvents the problems associated with the analysis of hybrids produced from emasculated plants. We identified hybrid combinations exhibiting mid-parent heterosis for vegetative fresh weight ranging from −9 to 103% and characterised heterosis in the reciprocal hybrids of one strongly heterotic combination. We found no evidence of a relationship between the extent of genetic relatedness of A. thaliana accessions and the strength of heterosis exhibited by their hybrids. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Changes in soil chemistry associated with the establishment of forest gardens on eroded,acidified grassland soils in Sri Lanka

Topsoil properties were determined in forest gardens established about 20 years ago on eroded grassland soils (abandoned tea lands) in the wet zone of the Sri Lankan highlands. They were compared with adjacent, eroded grasslands (abandoned tea lands) on strongly weathered soils vs soils at earlier stages of pedogenic development in a two-way analysis of variance. Soil pH in forest gardens was, on average, 6.1, nearly one unit higher than in the adjacent grasslands. In the garden soils, the cation exchange capacity (CEC measured at pH 4.8) was nearly double, exchangeable calcium concentrations five times and exchangeable magnesium three times as high as in the grasslands soils. Total soil N content was found to be nearly 40% higher in the gardens. Topsoil gravel contents in the gardens were less than half as high as in the grasslands. The increases in exchangeable bases and N in gardens, relative to grasslands, were attributed to increased nutrient retention and acquisition. Higher retention was partly due to the higher CEC_pH4.8, and probably to reduced erosion and increased, continuous fine root density in the garden topsoils. Higher field CEC in gardens was likely to result from generally higher C contents and from the reversal of acidification, presumably caused by base accumulation and decomposition processes. Our results suggest that forest garden establishment on degraded grasslands can lead to accumulation of mobile nutrients in the topsoil, probably due to increased nutrient retention, subsoil uptake and litter input exceeding nutrient uptake by the standing biomass.     

Crossing the thresholds: human ecology and historical patterns of landscape degradation

In discussions of landscape sensitivity, human activities have generally been regarded as external forces contributing to landscape change, with a focus on the impacts of cultivation methods, fertiliser practices, grazing pressures and atmospheric pollution. However, there has been comparatively little study undertaken that integrates physical and social systems in a historic context to explain the basis of human activity in sensitive landscapes. Where such attempts have been made, the manner of common land management has figured prominently, with ‘tragedy of the commons’ concepts used to explain land degradation and to provide a foundation for policy response. This has also been the case in Southern Iceland and in this paper we assess the extent to which common land domestic grazing pressures were the primary external force causing soil erosion and land degradation during the period of occupation from ca. 874 AD. We first provide field observation of soil erosion, temporally defined by tephrochronology, to highlight the extent of land degradation during this period. The ‘tragedy of the commons’ explanation of degradation is then assessed by evaluating historic documentary sources, and by environmental reconstruction and modeling of historic grazing pressures. These analyses indicate that regulatory mechanisms were in place to prevent overgrazing from at least the 1200s AD and suggest that there was sufficient biomass to support the numbers of domestic livestock indicated from historic sources. We suggest that failure to remove domestic livestock before the end of the growing season and an absence of shepherding were more likely to contribute to land degradation than absolute numbers. Lack of appropriate regulation of domestic livestock on common grazing areas can be attributed to limited cultural knowledge of changing and rapidly fluctuating environmental conditions.