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141.
142.
Albrecht Hase 《Die Naturwissenschaften》1938,26(14):223-224
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Vanessa L. Bonanno Albrecht I. Schulte-Hostedde 《Behavioral ecology and sociobiology》2009,63(6):835-846
Sperm competition is widespread in mammals and occurs when ejaculates from two or more males compete within the female’s reproductive
tract to fertilize the ova. Enlarged testes are associated with sperm competition because they produce sperm, but the accessory
glands produce fluids and proteins that are also important for fertilization success. Sperm morphology can also have consequences
for fertilization success because of its influence on sperm motility. Red squirrels engage in multiple mating, and thus sperm
competition is likely. Here, we assess levels of multiple paternity in a natural population of red squirrels, test the prediction
that testis size is correlated with size of the accessory glands and sperm morphometry, and test the prediction that ejaculate
investment is condition-dependent. Five of six litters (83%) showed evidence of multiple paternity, indicating that sperm
competition is likely to have occurred. Testis size was correlated with the size of all three accessory glands (prostate,
seminal vesicle, epididymides), and there was a generally positive relationship between the size of the accessory glands and
sperm length. Sperm morphology showed significant variation in size and shape among individual male squirrels. There was no
evidence of condition dependence of testis size or the size of the accessory glands, but sperm midpiece length was negatively
related to body condition. Further work should include determining the fitness consequence of variation in sperm morphometry,
testis size, and accessory gland size, and determining the effects of variation in ejaculate investment on sperm motility. 相似文献
148.
Incorporating soil structure and root distribution into plant uptake models for radionuclides: toward a more physically based transfer model 总被引:1,自引:0,他引:1
Albrecht A Schultze U Liedgens M Flühler H Frossard E 《Journal of environmental radioactivity》2002,59(3):329-350
Most biosphere and contamination assessment models are based on uniform soil conditions, since single coefficients are used to describe the transfer of contaminants to the plant. Indeed, physical and chemical characteristics and root distribution are highly variable in the soil profile. These parameters have to be considered in the formulation of a more realistic soil-plant transfer model for naturally structured soils. The impact of monolith soil structure (repacked and structured) on Zn and Mn uptake by wheat was studied in a controlled tracer application (dye and radioactive) experiment. We used Brilliant Blue and Sulforhodamine B to dye flow lines and 65Zn and 54Mn to trace soil distribution and plant uptake of surface-applied particle-reactive contaminants. Spatial variation of the soil water content during irrigation and plant growth informs indirectly about tracer and root location in the soil profile. In the structured monolith, a till pan at a depth of 30 cm limited vertical water flow and root penetration into deeper soil layers and restricted tracers to the upper third of the monolith. In the repacked monolith, roots were observed at all depths and fingering flow allowed for the fast appearance of all tracers in the outflow. These differences between the two monoliths are reflected by significantly higher 54Mn and 65Zn uptake in wheat grown on the structured monolith. The higher uptake of Mn can be modelled on the basis of radionuclide and root distribution as a function of depth and using a combination of preferential flow and rooting. The considerably higher uptake of Zn requires transfer factors which account for variable biochemical uptake as a function of location. 相似文献
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We report on the oldest European songbird (Passeriformes), from the early Oligocene (30–34 million years ago) of Frauenweiler in Germany. The specimen represents the earliest associated remains of an early Tertiary passerine described so far. It ties the first appearance of Passeriformes in Europe to a minimum age of 30 million years. Passeriform birds are absent in Eocene deposits that yielded abundant remains of small land birds and apparently dispersed into Europe around the Eocene/Oligocene boundary (about 34 million years ago), not at the Oligocene/Miocene boundary (about 24 mya) as hitherto thought. This possibly relates the appearance of songbirds in Europe to a well-known major faunistic break at the Eocene/Oligocene boundary, called the grande coupure. The Frauenweiler songbird most notably differs from extant Passeriformes in having a larger processus procoracoideus on the coracoid and appears to be outside Eupasseres, the taxon which includes Oscines (all modern European and most Old World songbirds) and Suboscines (most South and Central American songbirds). It shows that there were earlier dispersal events of non-oscine songbirds into Europe before the arrival of Oscines from the Australian continental plate towards the late Oligocene. 相似文献