ИСТИНА

Geographical variation of sexual dimorphism in growth rate and body size in mature Rana arvalis collected in five distinct localities was studied by comparing body length and age. Sex-specific growth rates and the degree of expression of sexual differences in body length and age composition change from the south-west to the north-east. The average age was higher in females (than in males) from two northern populations, but lower in females from three southern populations. Such differences depend not only on the duration of the activity season, but also on local conditions that caused differences in female and male survival. These differences, in turn, caused differences in age at maturity, age composition of breeding females, and in their contribution to reproduction even between populations from localities with similar duration of the activity season. The reasons for relatively low growth rates and relatively high survival in males from southern populations remain unclear.