Trakia Journal of Sciences, Vol. 12, № 1, 2014 1 Trakia Journal of Sciences, No 1, pp 1-12, 2014 Copyright © 2014 Trakia University Available online at: http://www.uni-sz.bg ISSN 1313-7050 (print) ISSN 1313-3551 (online) Original Contribution COLOUR POLYMORPHISM, SEX RATIO AND AGE STRUCTURE IN THE POPULATIONS OF PELOPHYLAX RIDIBUNDUS AND PSEUDEPIDALEA VIRIDIS (AMPHIBIA: ANURA) FROM ANTHROPOGENICALLY POLLUTED BIOTOPES IN SOUTHERN BULGARIA AND THEIR USAGE AS BIOINDICATORS Zh. Zhelev 1* , At. Arnaudov 1 , P. Boyadzhiev 2 1 Department of Human Anatomy and Physiology, Faculty of Biology, University of Plovdiv “Paisii Hilendarski”, Plovdiv, Bulgaria 2 Department of Zoology, Faculty of Biology, University of Plovdiv “Paisii Hilendarski”, Plovdiv, Bulgaria ABSTRACT This work presents data on the occurrence of colour polymorphism, sex ratio and age structure (among adult individuals actually involved in the breeding process) in populations of two tailless amphibian species – Pelophylax ridibundus and Pseudepidalea viridis inhabiting anthropogenically polluted biotopes in Southern Bulgaria. The habitats are adjacent to the reservoirs “Rozov Kladenets” (pollution of household waste origin: nitrite nitrogen, suspended solids and of industrial origin: coal dust, sulfates) and “Topolnitsa” (heavy metal pollution). It was established for both biotopes with P. ridibundus populations that the individuals with the striata morph predominate in both sexes. In P. viridis populations, in the two sexes, individuals with morphs A and C predominate. In the biotope contaminated with heavy metals (the “Topolnitsa” reservoir) the female individuals predominate in both tailless amphibian populations. In both biotopes the main part of the breeding marsh frogs are of the middle age group (2+). While in the “Rozov Kladenets” reservoir the males predominate in this age group, in the “Topolnitsa” reservoir predominate the females. In animals of the senior age groups in both biotopes predominate the females (mainly of the 3+age group). In P. viridis populations in both biotopes among the breeding animals (in both sexes) predominate individuals from the 2+ and 3+ age groups. In both amphibians, animals of the age groups 4 + and 5 + are very rare (females). It was found that under bad living conditions in ponds used for reproduction, the populations of both tailless amphibians grow better in the area of the “Rozov Kladenets” reservoir. Key words: anthropogenic pollution, biomonitoring, marsh frog, green toad, striata, maculata morphs, sexual, age differentiation. INTRODUCTION Currently, anthropogenic pollution is a global phenomenon and world-wide, there are almost no areas unaffected by this problem. ______________________________ *Correspondence to: Zhivko M. Zhelev University of Plovdiv “Paisii Hilendarski”, Faculty of Biology, Department of Human Anatomy and Physiology, 24 Tsar Assen Str., 4000 Plovdiv, Bulgaria; *Corresponding author e-mail: zhivko-m@uni- plovdiv.bg Amphibians, being consumers on several levels and inhabiting the border between two environments - land and water, are an important link in the food chain of an ecosystem. They are sensitive to changes in the environment and react with various modifications affecting both the functional systems of the organism and the population characteristics. This explains the increased interest in this class in recent years in the context of its use for the purposes of bioindication and biomonitoring (1-5).