Development of geographic variation of body size and reproductive characteristics in Rana arvalis females

The aim of our work was to identify the nature of geographic variation in age structure, body length and reproductive characteristics of Rana arvalis females, as well as interrelations between these characteristics according to the research data of some geographically distant populations of this species. The material was collected in several regions of Ukraine, Belarus and Russia. In total, 2483 adult females were studied. We conducted a comparative analysis of age structure, body size and female reproductive characteristics between distantly separated populations of Rana arvalis within species range. In north-eastern populations with the shortest activity season (3.8 months), females bred for the first time after the 4 ^th wintering and relatively seldom - after the 3rd wintering. Five-year-old and older females were rare. In central populations, the first breeding of 2-year-old females was very rare, most of females bred at the age of three or four, while most of four-year-old females reproduced for the first time. The maximum life-span was 10 years. In southern populations, with maximal duration of activity season (7.5 months), about one-half of females bred after the 2nd wintering for the first time, the rest bred after the 3rd wintering. The proportion in four-year-old females was about equal to that of in 2-year-olds, whereas the proportion of older females was very low. In populations with the activity season close to the shortest, the relative low population mean values of female body length were revealed. Apparently, a relatively small body size and low fecundity in females from north-eastern populations were due to low mean age as the result of high mortality after reaching maturity. Mean egg diameter (both absolute value and adjusted by body length means) was maximal in females from the north-eastern population. In all studied populations, age differences have more impact on egg size than on fecundity, and it was not revealed for relative clutch mass. In contrast to age, female body length has more impact on fecundity than on egg size. In southern populations, the contribution of fecundity into reproductive effort was the highest and was attained by simultaneous increase in fecundity and egg diameter that was suggested by significant positive correlation between these two characteristics. In northern populations, the decrease in fecundity into reproductive effort was not connected with increase in egg size which can be explained by stronger influence of body length than age on fecundity and weaker influence - on egg size. However, in all populations, the contribution of fecundity into reproductive effort was much higher than egg diameter. As an exception, we revealed a sufficient decrease both in egg diameter and fecundity in the youngest females that bred for the first time.

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