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81.
Response of Two Heat Shock Genes to Selection for Knockdown Heat Resistance in Drosophila Melanogaster 总被引:1,自引:0,他引:1 下载免费PDF全文
To identify genes involved in stress resistance and heat hardening, replicate lines of Drosophila melanogaster were selected for increased resistance to knockdown by a 39° heat stress. Two selective regimes were used, one with and one without prior hardening. Mean knockdown times were increased from ~5 min to >20 min after 18 generations. Initial realized heritabilities were as high as 10% for lines selected without hardening, and crosses between lines indicated simple additive gene effects for the selected phenotypes. To survey allelic variation and correlated selection responses in two candidate stress genes, hsr-omega and hsp68, we applied denaturing gradient gel electrophoresis to amplified DNA sequences from small regions of these genes. After eight generations of selection, allele frequencies at both loci showed correlated responses for selection following hardening, but not without hardening. The hardening process itself was associated with a hsp68 frequency change in the opposite direction to that associated with selection that followed hardening. These stress loci are closely linked on chromosome III, and the hardening selection established a disequilibrium, suggesting an epistatic effect on resistance. The data indicate that molecular variation in both hsr-omega and hsp68 contribute to natural heritable variation for hardened heat resistance. 相似文献
82.
Microarrays have been used to examine changes in gene expression underlying responses to selection for increased stress resistance in Drosophila melanogaster, but changes in expression patterns associated with increased resistance to cold stress have not been previously reported. Here we describe such changes in basal expression levels in replicate lines following selection for increased resistance to chill coma stress. We found significant up- or down-regulation of expression in 94 genes on the Affymetrix Genome 2.0 array. Quantitative RT-PCR was used to confirm changes in expression of six genes. Some of the identified genes had previously been associated with stress resistance but no previously identified candidate genes for cold resistance showed altered patterns of expression. Seven differentially expressed genes that form a tight chromosomal cluster and an unlinked gene AnnX may be potentially important for cold adaptation in natural populations. Artificial selection for chill coma resistance therefore altered basal patterns of gene expression, but we failed to link these changes to plastic changes in expression under cold stress or to previously identified candidate genes for components of cold resistance. 相似文献
83.
The population ofDrosophila melanogaster inside the wine cellar of Chateau Tahbilk of Victoria, Australia was found by McKenzie and Parsons (1974) to have undergone microevolution for greater alcohol tolerance when compared to the neighboring population outside the cellar. This triggered additional studies at Tahbilk, and at other wine cellars throughout the world. The contributions and interactions of researchers and the development of ideas on the ecology and genetics of this unique experimental system are traced. Although the ADH-F/ADH-S polymorphism was found to be maintained by selection in the Tahbilk populations, the selection is not significantly associated with alcohol tolerance. The environment inside the Tahbilk wine cellar is not as rich in ethanol as was originally anticipated, and selection that affects the alcohol dehydrogenase polymorphism may be more concerned with the relative efficiency with which ethanol is used as a nutrient byD. melanogaster. The synthesis and modification of lipids, particularly in membranes, appears to be important to alcohol tolerance. The studies of the Tahbilk population are at a crossroad. New experimental approaches promise to provide the keys to the selection that maintains the alcohol dehydrogenase polymorphism, and to factors that are important to alcohol tolerance and stress adaptation. From these research foundations at Tahbilk very significant contributions to our future understanding of the genetic processes of evolution can be made. 相似文献
84.
Sam McKechnie 《New Zealand journal of zoology.》2013,40(4):259-265
Abstract Seabirds can influence entire island ecosystems through the effects of their burrowing and of their underground deposition of vegetation on biotic and abiotic island processes. This study quantifies the extent of these effects at three sooty shearwater breeding islands in southern New Zealand, with the aim of assessing the importance of this species as an ecosystem engineer. Mean burrow volumes ranged between 158.2 and 528.1 m3 ha–1. Between 18 and 34% of the ground surface was undermined by burrow space on the three islands. This extent of burrowing is comparable to that of fossorial mammals, widely recognised as ecosystem engineers. Mean vegetation inputs (dry weight), transported underground by birds and incorporated into nests, varied between 33 and 96 g m‐2 The implications of the biopedturbation caused by sooty shearwater burrowing to the extent measured in this study may be profound for some ecosystem processes, and certainly warrants further research. 相似文献
85.
McKechnie AE 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(3):235-247
Comparative analyses of avian energetics often involve the implicit assumption that basal metabolic rate (BMR) is a fixed,
taxon-specific trait. However, in most species that have been investigated, BMR exhibits phenotypic flexibility and can be
reversibly adjusted over short time scales. Many non-migrants adjust BMR seasonally, with the winter BMR usually higher than
the summer BMR. The data that are currently available do not, however, support the idea that the magnitude and direction of
these adjustments varies consistently with body mass. Long-distance migrants often exhibit large intra-annual changes in BMR,
reflecting the physiological adjustments associated with different stages of their migratory cycles. Phenotypic flexibility
in BMR also represents an important component of short-term thermal acclimation under laboratory conditions, with captive
birds increasing BMR when acclimated to low air temperatures and vice versa. The emerging view of avian BMR is of a highly
flexible physiological trait that is continually adjusted in response to environmental factors such as temperature. The within-individual
variation observed in avian BMR demands a critical re-examination of approaches used for comparisons across taxa. Several
key questions concerning the shapes and other properties of avian BMR reaction norms urgently need to be addressed, and hypotheses
concerning metabolic adaptation should explicitly account for phenotypic flexibility. 相似文献
86.
87.
Rectal Carriage of Enterohemorrhagic Escherichia coli O157 in Slaughtered Cattle 总被引:1,自引:0,他引:1 下载免费PDF全文
J. Christopher Low Iain J. McKendrick Caroline McKechnie David Fenlon Stuart W. Naylor Carol Currie David G. E. Smith Lesley Allison David L. Gally 《Applied microbiology》2005,71(1):93-97
Escherichia coli O157:H7 is an important cause of diarrhea, hemorrhagic colitis, and potentially fatal human illness. Cattle are considered a primary reservoir of infection, and recent experimental evidence has indicated that the terminal rectum is the principal site of bacterial carriage. To test this finding in naturally colonized animals, intact rectum samples from 267 cattle in 24 separate lots were obtained immediately after slaughter, and fecal material and mucosal surfaces were cultured for E. coli O157 by direct and enrichment methods. Two locations, 1 and 15 cm proximal to the recto-anal junction, were tested. In total, 35 animals were positive for E. coli O157 at at least one of the sites and 232 animals were negative as determined by all tests. The frequency of isolation and the numbers of E. coli O157 cells were higher at the site closer to the recto-anal junction, confirming our previous experimental findings. We defined low- and high-level carriers as animals with E. coli O157 levels of <1 × 103 CFU g−1 or <1 × 103 CFU ml−1 and animals with E. coli O157 levels of ≥1 × 103 CFU g−1 or ≥1 × 103 CFU ml−1 in feces or tissues, respectively. High-level carriage was detected in 3.7% of the animals (95% confidence interval, 1.8 to 6.8%), and carriage on the mucosal surface of the terminal rectum was associated with high-level fecal excretion. In summary, our results support previous work demonstrating that the mucosal epithelium in the bovine terminal rectum is an important site for E. coli O157 carriage in cattle. The data also support the hypothesis that high-level fecal shedding (≥1 × 103 CFU g of feces−1) of enterohemorrhagic E. coli O157 results from colonization of this site. 相似文献
88.
Diurnal body temperature patterns in free‐ranging populations of two southern African arid‐zone nightjars 下载免费PDF全文
Endotherms allocate large amounts of energy and water to the regulation of a precise body temperature (Tb), but can potentially reduce thermoregulatory costs by allowing Tb to deviate from normothermic levels. Many data on heterothermy at low air temperatures (Ta) exist for caprimulgids, whereas data on thermoregulation at high Ta are largely absent, despite members of this taxon frequently roosting and nesting in sites exposed to high operative temperatures. We investigated thermoregulation in free‐ranging rufous‐cheeked nightjars Caprimulgus rufigena and freckled nightjars Caprimulgus tristigma in the southern African arid zone. Individuals of both species showed labile Tb fluctuating around a single modal Tb (Tb‐mod). Average Tb‐mod was 39.7°C for rufous‐cheeked nightjars and 39.0°C for freckled nightjars. In both species, diurnal Tb increased with increasing Ta. At Ta ≥ 38°C, rufous‐cheeked nightjar mean Tb increased to 42°C, equivalent to 2.3°C above Tb‐mod. Under similar conditions, freckled nightjar Tb was on average only 1.1°C above Tb‐mod, with a mean Tb of 40.0°C. Freckled nightjars are one of the most heterothermic caprimulgids investigated to date, but our data suggest that during hot conditions this species maintains Tb within a narrow range above Tb‐mod, possibly reflecting an evolutionary tradeoff between decreased thermal sensitivity to lower Tb but increased sensitivity to high Tb. These findings reveal how general thermoregulatory patterns at similar Ta can vary even among closely related species. 相似文献
89.
90.
Southern analysis of the Adh region of 212 Drosophila melanogaster lines collected from the Tahbilk winery revealed linkage disequilibrium between a 37-bp insertion [designated delta 2 by Kreitman (1983)] and the fast electrophoretic variant of alcohol dehydrogenase (ADH-F). Among these lines 34% contained the insert and encoded ADH-F, 33.5% encoded ADH-F and did not have the insert, and 32.5% encoded the slow electrophoretic variant of alcohol dehydrogenase (ADH-S). Strong linkage association between this insert and ADH-F is evident worldwide. Twenty-nine of the second chromosome lines were characterized for ADH protein quantity by using radial immunodiffusion. ADH quantity was estimated in both larvae and adult males raised in the presence and absence of alcohol supplement to each of two different food media. Analyses of variance indicated higher levels of ADH protein in larvae from lines with the insert (all ADH-F), compared with those without (both ADH-F and ADH-S), independent of either dietary alcohol or media type. No such difference in ADH quantity between insert- and noninsert-containing ADH-F lines was detected in adults, although the expected higher levels occurred in ADH-F lines compared with ADH-S lines. Given the high levels of linkage disequilibrium in the Adh region, these data suggest that either polymorphic nucleotide-site variants positively associated with delta 2 on the second chromosome or delta 2 itself increases larval levels of ADH protein. 相似文献