Sexual Dimorphism in Digit Length Ratios in Marsh Frog, Pelophylax Ridibundus (Ranidae) from Iran

Sexual dimorphism in digit length ratios (preliminary 2D: 4D) is a morphological feature that affected by prenatal androgenic hormone during development. This dimorphism is controlled by the expression of home box genes which are highly conserved among vertebrate taxa. It is predicted that in most mammals, females have larger digit ratios than males and in diapsid species, males have larger digit ratios than females. However, this trend has not been studied sufficiently in lower taxa. In this study we examined this hypothesis in 50 specimen of marsh frog in north of Iran. Digit length and snout- ventral length (SVL) of frogs were measured by vernier caliper. The data analyzed by SPSS software version 18. The results showed unlike more basal vertebrate taxa, in marsh frog females had larger 2D: 4D than males. The digit length of D1 and D3 between males and females were significantly difference (P 0.05). We did not observe any correlation between SVL and digit ratios. Nevertheless there were positive correlation between SVL and sex. We conclude that the evolution of morphological digits in frogs, deserve more attention, because it may be controlled by the association between prenatal exposure and environmental effects.