Rozród norników - reakcja na zmiany składu pokarmu czy efekt matczyny?

Abstract

Onset and duration of microtine reproduction varies with the cycle phase in cyclic populations and is temporally stable in non-cyclic populations. This reproductive variation has been related to annually more or less varying growth rates, including varying contents of chemical stimuli of food plants, or to effects of maternal condition, especially nutrition, on the reproductive performance of the succeeding generation. To distinguish between these two explanations, immatures of Microtus agrestis were caught at annual density peaks in south Sweden and were kept under constant laboratory conditions but natural light and on a simplified food with stable composition for one year or until reproduction ended. Their young were kept in exactly the same way. The second generation animals showed a two month earlier start of reproduction and common winter breeding but not higher reproductive output than their mothers. Neither start nor end of breeding in these animals could have been due to chemical cues alone. It is concluded that delay effects will be especially important in cyclic populations but that at present we are unable to evaluate the varying effects of delay, tracking and social influences on the overridingly important photoperiodic regulation of reproduction.