Population biology of hemiclonal waterfrogs     (Europe, 1991-present) Evolutionary theory predicts that inter-specific hybrids and organisms with clonal or hemiclonal reproduction are at a selective disadvantage in comparison with genuine and sexually repro- ducing species. Yet, some of the allegedly handicapped organisms have existed for more than 200'000 generations, occur over wide geographical ranges and maintain large populations. We use the hemiclonal Edible Frog (Pelophylax esculentus) - originally a hybrid between the Pool Frog (P. lessonae) and the Lake or Marsh Frog (P. ridibundus) - as a model system to investigate the genetic, behavioural and ecological reasons for this unexpected ecological and evolutionary success. The hybrid reproduces hybridogenetically, i.e. it eliminates one parental genome from the germ line prior to meiosis and clonally transmits the other parental genome to eggs and sperm, respectively. Our specific questions include: • What factors and determine the size, composition and dynamics of populations in which hybrids occur alone or in sympatry with the parental species? • How do different ecological conditions affect mating success and survival rates of hybrid and parental individuals? • Do the routes to polyploidy and the mechanisms maintaining it vary between different regions of the geographical distribution area? The results from our field studies, laboratory experiments and mathematical models can help to understand a variety of more general biological issues. These include sexual conflicts, the stabi- lity of hybrid zones, the evolutionary potential of (hemi-) clonal taxa for speciation, the dynamics of tightly coupled systems (e.g. parasite-host), and the question: how do behavioural strategies of individuals affect the composition and dynamics of populations and communities?