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Esa Koskela Pinja Juutistenaho Tapio Mappes Tuula A. Oksanen 《Evolutionary ecology》2000,14(2):99-109
According to parental investment theory, nest defence activity should be related to the reproductive value of the offspring.
Alternative hypotheses suggest that defence activity may, for example, depend upon the conspicuousness of the young. Studies
concerning this topic have been carried out almost exclusively on birds and experimental data on the diversity of organisms
is lacking. Bank voles Clethrionomys glareolus were used to study the effects of the number and age of offspring upon the pup defence activity of mothers. Male bank voles
are infanticidal and thus an adult male was used as a predator. Defence trials were conducted in the laboratory and filmed
for subsequent analysis. Litter sizes were divided into three treatment groups: reduced (−2 pups), control (±0 pups) and enlarged
(+2 pups). In order to study the effect of offspring age upon maternal defence activity the trials were conducted twice: when
the pups were 3 and 8 days old. Defence activity increased with the number of offspring and enlarged litters were most actively
defended. This result supports parental investment theory and conclusions drawn by earlier studies of birds. However, in contrast
to the conclusions of earlier studies, older offspring were defended less than the younger ones. Whilst new-born pups are
totally defenceless against predators their vulnerability decreases as they age. Therefore, we suggest that maternal aggression
in female bank voles is related to the value as well as to the vulnerability of the offspring. The validity of this explanation
and the determinants of parental investment decisions in small mammals in general deserve further study.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献