Koskela Esa
Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland Fax: +358-14-602321; e-mail:
Oecologia. 1998 Jul;115(3):379-384. doi: 10.1007/s004420050531.
To estimate the optimality of brood size, it is essential to study the effects of brood size manipulation on offspring survival and reproductive success. Moreover, testing the generality of the hypothesis of reproductive costs requires experimental data from a diversity of organisms. Here I present data on the growth, survival and reproductive success of bank vole Clethrionomys glareolus individuals from manipulated litters. Furthermore, the survival of mothers whose litter size was manipulated was studied. At weaning, the mean weight of pups from enlarged litters was lower and from reduced litters higher compared to control litters. After winter, at the start of the breeding season, individuals from enlarged litters, especially males, were still lighter than individuals from the other two treatments. Litter enlargements did not increase the number of reproducing female offspring per mother, nor did the litter sizes of female offspring differ between treatments. There were no differences between treatments in winter survival of offspring after weaning, but among female offspring, weaning weight explained the survival probabilities over winter. A higher weight of females at winter determined the probability of starting to reproduce in spring. The survival of mothers did not seem to be influenced by litter manipulation performed the previous year. According to the results, mothers nursing enlarged or reduced litters do not gain any fitness benefits in terms of number of offspring surviving to breeding. The results are consistent with the majority of experiments conducted in birds, which have found costs of enlarged brood appearing as offspring trade-offs rather than parent trade-offs.
为了估计窝仔数的最优性，研究窝仔数操纵对后代存活和繁殖成功率的影响至关重要。此外，检验繁殖成本假说的普遍性需要来自多种生物的实验数据。在此，我展示了来自经过操纵的窝仔的棕背䶄（Clethrionomys glareolus）个体的生长、存活和繁殖成功率的数据。此外，还研究了窝仔数被操纵的母鼠的存活情况。在断奶时，与对照窝仔相比，来自扩大窝仔的幼崽平均体重较低，而来自减少窝仔的幼崽平均体重较高。冬季过后，在繁殖季节开始时，来自扩大窝仔的个体，尤其是雄性，仍然比其他两种处理的个体轻。窝仔数扩大并没有增加每只母鼠繁殖的雌性后代数量，不同处理之间雌性后代的窝仔数也没有差异。断奶后后代的冬季存活情况在不同处理之间没有差异，但在雌性后代中，断奶体重解释了冬季的存活概率。冬季雌性体重较高决定了春季开始繁殖的概率。母鼠的存活似乎不受前一年进行的窝仔操纵的影响。根据结果，哺育扩大或减少窝仔的母鼠在存活到繁殖期的后代数量方面没有获得任何适应性益处。这些结果与在鸟类中进行的大多数实验一致，这些实验发现扩大窝仔的成本表现为后代之间的权衡，而非亲代之间的权衡。
