The Pelophylax esculentus complex in North-Western Romania: distribution of the population systems

The aim of this study was to clarify the distribution of the Pelophylax esculentus complex population systems in north-western Romania. The study area is represented by north-western Romania including the administrative territories delineated by Arad, Bihor and Satu-Mare counties. Surveys were conducted between September 2004 and May 2009. There were herpetofaunistically surveyed 884 geographic localities in north-western Romania. In 666 of these localities it was identified/reconfirmed the presence of water frogs from the P. esculentus complex (666-ridibundus, 97-esculentus, 33-lessonae). There were identified 39 distinct populations of P. lessonae and 127 populations of P. kl. esculentus respectively. In areas where all the three forms of water frogs or at least two of them are present, there were identified 127 population systems: R-E (83), L-R-E (39) and E (5). In all populations of water frogs from north-western Romania, the parental species (P. ridibundus, P. lessonae) are represented both by males and females. Concerning the hybrid P. kl. esculentus we could not identify males of this form in every population, the females being able to reproduce with the males of parental species. In the case of two populations of P. Id. esculentus we have not identified males (all-females E system). It is possible that these populations are included in a parthenogenetic cycle. During the study, mixed pairs in amplexus were identified exclusively between males of P. lessonae and females of P. Id. esculentus, and between males of P. Id. esculentus and females of P. ridibundus, being also identified several spawns. Most of the L-R-E system populations are found in Carei Plain and Livada Plain (the Tur Valley). Conservation in time of these populations is also ensured by their placement in Natura 2000 Habitats Directive sites.