Age-specific effect of parity on litter size in the common vole (Microtus arvalis)

The "triangular" pattern of reproduction in arvicoline rodents predicts sma ll fecundity early and late in life and high fecundity in the middle. In pr oducing this pattern, the effects of maternal age and parity are typically highly confounded. We present results of a laboratory study designed to dis entangle these effects in the common vole (Microtus arvalis) by analyzing v ariation in sizes of the first 2 litters born to 3 age classes of females s ubjected to photoperiods of 8 h and 16 h of light. Although the youngest fe males, paired at 2 weeks of age, decreased size of the 2nd litter in either light environment, the older 2 classes, paired at 3-4 months and 1 year of age, increased their 2nd litters, as predicted by the triangular pattern. This age-specific effect of parity could be explained by differences in the size of 1st litters.