Study of digit lengths ratios in marsh frog,Pelophylax ridibundus (Ranidae) from Iran

We studied the sexual dimorphism in digit length ratio as a possible biomarker of steroid hormones exposure in a population of Pelophylax ridibundus from north of Iran. Human males tend to have lower digit ratios than females, and it has been speculated that these trends should be visible in other tetrapod vertebrates. Digit ratio has not been measured in more basal taxa such as amphibians. However, there is controversial information about the different populations of tetrapods and suggest that sexual dimorphism specific in the digits proportions is much more complex. In this study, digit ratio was measured in 30 males and 20 females of adult marsh frogs to investigate the existence and patterning of sexual dimorphism. Female frogs had commonly larger digits than males. The 2D:4D ratio of the front feet varied significantly by sex with females having a larger ratio than males. These results indicate that 2D: 4D in marsh frog is both sexually dimorphic and follows a pattern between the sexes similar to that of most tetrapod species. Therefore, our findings provide more evidence that digit ratios are sexually dimorphic in amphibian species and this species may represent valuable animal models for experimental tests of the association between prenatal exposure to androgens or estrogens and digit ratios. The genetic link between limb development and the urogenital system had been established with the evolution of the earliest terrestrial tetrapods.

Keywords:

Marsh frog , Dimorphism , Digit ratio