ECOLOGICAL STATUS OF THE SAZLIYKA RIVER AND ITS TRIBUTARIES (BLATNITSA AND SOKOLITSA) AS INDICATED BY THE COLOR POLYMORPHISM AND SEXUAL COMPOSITION OF THE POPULATIONS PELOPHYLAX RIDIBUNDUS (AMPHIBIA: RANIDAE)

P. S. Boyadzhiev, Zh. M. Zhelev, A. D. Arnaudov

Abstract: The present work studies the nature of the distribution of colour polymorphism and the sexual composition (among adult, sexually mature individuals involved in the breeding process) in populations of marsh frog (Pelophylax ridibundus ) inhabiting different biotopes along one of the ecologically damaged rivers in Bulgaria (the river Sazliyka) and two of its left-side tributaries (the rivers Blatnitsa and Sokolitsa). The ecological conditions and the quality of the living environment were assessed based on these two population characteristics. it was found out that in habitats located in the upper reaches of the rivers Sazliyka and Sokolitsa, in the populations of P. ridibundus the two colour morphs of the coloration of the back (striata, maculata) are equally represented. At the same time, the ratio of individuals of both sexes is close to the theoretically expected 1:1 distribution in relatively clean waters. in habitats along the middle and lower reaches of the rivers Sazliyka and Sokolitsa
and the one of the river Blatnitsa, the environmental conditions are highly impaired: in the populations of P. ridibundus, the dominant morph striata is expressed. Moreover, the sex ratio has changed resulting in a predominance of the females.

Keywords: bioindication; maculata; morphs: striata; Pelophylax ridibundus; river Sazliyka; sexual composition

Date published: 2017-09-21