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491.
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
492.
Storch G 《Die Naturwissenschaften》2008,95(10):927-930
Most living mammal orders, including our own, started their career during the first 10 million years of the Cenozoic, the
Age of Mammals. The fossil record documents that early Paleogene adaptive radiations of various clades included tiny species
of the size of living shrews. Remains of particularly diminutive limb bones are described from the late Paleocene site of
Walbeck, Sachsen-Anhalt. Discovered in 1939, it has remained the only known Paleocene mammal-bearing locality from Germany.
The remains are referred to the family Adapisoriculidae, which is considered on the basis of the present postcranial evidence
to represent plesiadapiform primates rather than alleged lipotyphlan insectivores as previously proposed. The Walbeck fossils
compete with the Early Eocene species Toliapina vinealis from Europe and Picromomys petersonorum from North America for the status of the smallest known primate, fossil and living. Their estimated body weights are as small
as 10 g. The limb bones show features related to enhanced flexion at the elbow and hip joint, suggesting arboreal habits and
environments such as terminal branches. The diminutive size and tooth morphology suggest feeding on small insects and other
invertebrates. Postcranials are important to assess early radiations, such tiny specimens as the present ones are extremely
scarce in the fossil record, however. 相似文献
493.
The platinum group elements (PGE) Pt, Pd and Rh are increasingly emitted into the environment by automobile catalytic converters. Whereas the biological availability of PGE to plants and animals has been demonstrated, only few studies concentrate on the influence of PGE on a cellular level. The effects of Pt, Pd and Rh compared with Cd, Ni and Cr on cell viability and oxidative stress response using soluble metal salts were studied in the human bronchial epithelial cell line BEAS-2B. Whilst Rh(III) showed little influence, both Pt(II) and Pt(IV) as well as Pd(II) had significant effects on cell viability at levels comparable to Cd(II) and Cr(VI). Arranging metal species in order of increasing toxicity as determined by LC50 yields: Rh(III)=1.2 mmol/L相似文献