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51.
Mammalian hibernation, which lasts on average for about 6 months, can reduce energy expenditure by >90% in comparison to active
individuals. In contrast, the widely held view is that daily torpor reduces energy expenditure usually by about 30%, is employed
for a few hours every few days, and often occurs only under acute energetic stress. This interpretation is largely based on
laboratory studies, whereas knowledge on daily torpor in the field is scant. We used temperature telemetry to quantify thermal
biology and activity patterns of a small arid-zone marsupial, the stripe-faced dunnart Sminthopsis macroura (16.9 g), in the wild and to test the hypothesis that daily torpor is a crucial survival strategy of this species in winter.
All individuals entered torpor daily with the exception of a single male that remained normothermic for a single day (torpor
on 212 of 213 observation days, 99.5%). Torpor was employed at air temperatures (T
a) ranging from approximately −1°C to 36°C. Dunnarts usually entered torpor during the night and aroused at midday with the
daily increase of T
a. Torpor was on average about twice as long (mean 11.0 ± 4.7 h, n = 8) than in captivity. Animals employed sun basking during rewarming, reduced foraging time significantly, and occasionally
omitted activity for several days in sequence. Consequently, we estimate that daily torpor in this species can reduce daily
energy expenditure by up to 90%. Our study shows that for wild stripe-faced dunnarts daily torpor is an essential mechanism
for overcoming energetic challenges during winter and that torpor data obtained in the laboratory can substantially underestimate
the ecological significance of daily torpor in the wild. 相似文献
52.
No evidence for sperm priming responses under varying sperm competition risk or intensity in guppies
Jonathan P. Evans 《Die Naturwissenschaften》2009,96(7):771-779
Sperm competition theory predicts that males should tailor their investment in ejaculates according to the number of rival
males competing to fertilize a female’s eggs. Research spanning several taxa supports this prediction by showing that males
are often sensitive to the level of sperm competition and adjust their investment in sperm numbers accordingly. More recent
work has revealed that males may also tailor the quality of sperm according to the number of males competing for fertilization.
Here I test for both effects in guppies (Poecilia reticulata) in an experiment that simultaneously evaluates the risk and intensity models of sperm competition. The experiment determined
whether male guppies adjust the number (stripped ejaculate size) and quality (sperm velocity and viability) of sperm that
are primed over a 3-day period according to experimental changes in the perceived level of sperm competition. A total of 136
focal males were initially stripped of all retrievable sperm and assayed for these sperm traits before being allocated at
random to one of four treatments simulating different levels of sperm competition risk and intensity. During the 3-day treatment
phase, focal males had visual and olfactory access to a sexually receptive (initially virgin) female maintained with different
numbers of stimulus males to simulate variation in the risk and intensity of sperm competition. Following this, males were
assayed again for the sperm traits. Contrary to predictions, there was no significant change in any of the measured variables
among treatments, although qualitatively the patterns for sperm velocity and viability did conform to expectation. The lack
of any trend for the number of sperm primed was unequivocal and future work examining the effects of sperm competition on
sperm production should focus on whether males differentially allocate sperm numbers among matings that differ in the level
of sperm competition. 相似文献
53.
本文基于财政"节能环保"支出科目,整合散落在其他科目里的生态环境保护支出,分析中央财政(含本级投入与专项转移支付)近五年(2012—2016年)的生态环境保护支出现状,发现:中央用于生态建设和保护方面的支出最多,五年支出均值为933.1亿元;其次是环境污染治理支出,五年支出平均值为773.4亿元。同时,基于现状分析及工作实践发现中央财政生态环境保护支出存在规模偏小、比重偏低、增长的稳定性不足等问题,中央财政需进一步优化支出方向和结构,加强绩效评价和结果应用。 相似文献