Annual Ovarian Cycle in the Frog, Rana ridibunda, in Northern Greece

The annual ovarian cycle of the frog Rana ridibunda in northern Greece was studied from 1986 to 1988. Young females reached sexual maturity at a mass of 22-25 g and SVL of 62-66 mm. The maximum ovarian mass occurred in March and the minimum in August. Mass changes of the oviducts followed those shown by the ovaries. Three waves of oviposition were observed in a breeding season, and clutch size ranged from 500-7000 ova in the first wave of oviposition. The smallest ovarian follicles were observed in August and the largest in late February to early March. Females oviposit when the mass of their ovaries is at least 5% of the total body mass. Ovarian mass, clutch size, and ovum size were positively correlated with body mass. The masses of the fat body and liver peak in autumn at the onset of hibernation, and were reduced in spring after oviposition. A pause in the reproductive events was observed only in December and January. To estimate the total number of eggs, a por- tion of the ovary was weighed, and the eggs from this portion of the ovary were placed in petri dishes and counted. The total number of eggs from each female was then calculated. Ovum diameter was measured with an ocular micrometer to the nearest 0.001 mm. Clutch size was determined by counting the oviducal eggs from three females using a binocular micro- scope. The minimum ovum diameter observed (1.40 mm) was used as minimum diameter of the ovarian follicles for all the other months. Analysis of covariance (ANCOVA) was con- ducted, considering each variable (body length; masses of body, liver, fat bodies, ovary and ovi- ducts; number of ova; and ovum diameter) sep- arately, with the rest as covariates. The SPSS/ PC (1983) package was used for statistical pro- cedures.