Mappes Tapio, Koskela Esa
Department of Biological and Environmental Science, University of Jyvaskyla, P.O. Box 35, FIN-40014, Finland.
Evolution. 2004 Mar;58(3):645-50.
One of the main tenets of modern life-history theory is the negative relationship (trade-off) between the number and quality of offspring produced. Theory predicts a negative genetic correlation between these traits since both are closely related to fitness of individuals. However, the genetic basis of the trade-off has only been tested to a limited extent in natural populations. We examined whether size and quality of offspring are negatively related to litter size in the bank vole Clethrionomys glareolus. First, we found a significant negative phenotypic correlation between the number and size of offspring at birth in both laboratory and field populations of the bank vole. Second, a larger size at birth decreased the maturation age of female offspring in the laboratory, and increased the probability of breeding and the size of the first litter in the field. Furthermore, manipulation of offspring size at weaning indicated that structural effects of birth size in mammals have a more profound effect on the expression of life-history traits than weaning size. Finally, in addition to the phenotypic negative correlation between the number and size of offspring, we found evidence for a negative genetic correlation between these two traits, which confirms the genetic basis of the trade-off. This negative genetic covariation may have considerable effects on the rate and direction of evolution of the two related life-historical traits.
现代生活史理论的主要原则之一是所产生后代的数量与质量之间存在负相关关系（权衡）。理论预测这些性状之间存在负遗传相关性，因为两者都与个体的适合度密切相关。然而，这种权衡的遗传基础在自然种群中仅得到了有限程度的检验。我们研究了普通田鼠（Clethrionomys glareolus）后代的大小和质量是否与窝仔数呈负相关。首先，我们发现普通田鼠的实验室和野外种群中，出生时后代数量与大小之间存在显著的负表型相关性。其次，出生时较大的体型降低了实验室中雌性后代的成熟年龄，并增加了野外繁殖的概率和第一窝的大小。此外，对断奶时后代大小的操控表明，哺乳动物出生时大小的结构效应比断奶时大小对生活史性状表达的影响更为深远。最后，除了后代数量与大小之间的表型负相关外，我们还发现了这两个性状之间存在负遗传相关性的证据，这证实了这种权衡的遗传基础。这种负遗传协变可能对两个相关生活史性状的进化速率和方向产生相当大的影响。
