Estimation of the factors determining body size of young's of the year of Rana temporaria L. before a hibernation

According to special assessment of many investigators, a number of factors such as size at previous stage, density, duration of the larval stage etc. influences umbiguosly on the morthological variability of the youngs of the year of common frog, whose development takes place in unpredictable conditions of temporal ponds Here we present an analysis of a long-time series (22 years) of body length variations of common frog. The control population of Rana temporaria occupied about 60 ha within the «Kivach» Nature Reserve (Russia, Republic Karelia, 62° 16′ 35″ N, 33° 59′ E) with many breeding ponds and meadows suitable for juvenile frogs foraging. At the end of foraging period (early September), snout-vent length of juveniles in the samples of 34 individuals (on average) was measured with an accuracy of 0.1 mm, and the mean length of juvenile frogs was calculated. The dates of tadpole hutching and the beginning of metamorphosis were recorded. Weather data were obtained from the meteorological station located in the centre of the study area. The relationship between the final mean body length and independent variables was tested using a multiple regression approach. The final equation is as follows: Lсгл = 11.71 + 1.16•T1 – 0.02•Ос1 – 0.1•Д1 where Lсгл is the mean body length of juveniles, T1 is the mean daily air temperature during three summer month, °C, Ос1,days, is the amount of rainfall in July, mm, and Д1 is the duration of larval period (from the larval hutching up to the juvenile frogs emergence). The coefficient of determination for this dependence R2 = 0.61 (p = 0.0005). Thus, these variables explains 61% of the variance in the juveniles’ body length by the autumn. Herein, T1 explains 32.1%, Ос1 — 9.6%, and Д1 explain 19.6%, all values are significant. This equation and statistical analysis showed that the year-to-year morphological variability of juvenile frogs by the autumn depends on air temperature, rainfall, and the time of exposition (from the beginning of metamorphosis up to the end of foraging), rather than intrinsic properties of different groups of newly metamorphosed froglets.