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RESEARCH PRODUCT

Is triploidy indisputably determinable in hybridogenetic hybrids by planimetric analyses of erythrocytes?

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The size of amphibian erythrocytes is positively correlated to their DNA content. Therefore, planimetry of erythrocytes has long been used to determine ploidy levels in amphibians. In Rana esculenta. a hybrid originating from Rana ridibunda x Rana lessonae natural crosses, planimetric determination of erythrocyte size is used to distinguish diploid and triploid specimen. In the present study we performed planimetric analyses on the hybrid Rana grafi, comprising a second hybridogenetic system with its parental species Rana ridibunda and Rana perezi in southern parts of France. We found size differences of diploid and triploid erythrocytes to range between 26 and 33% in studies on adult R. esculenta and calculated a mean difference of 30%. Our results strongly support a significant influence of the factors snout-vent-length (SVL), geographic location, organic matter of substratum, and relative amount of oxygen on the erythrocyte size of these hybrids. Discriminant analyses proved a probability of approximately 30% to disaffiliate individuals in our data set and indicated that ploidy determinations on individuals will be most unprobable, if the SVL of individuals strongly staggers and the habitats differ in their environmental characteristics. Due to the found dependencies of the erythrocyte size to several factors we consider planimetric analysis for reasons of ploidy determination as unprobable and thus we favour more sophisticated techniques such as DNA-flowcytometry or karyotype analyses.