32. Jumping genes in frogs; cytogenetic evidence that additional ribosomal gene locations in Hyla chrysoscelis (Cope's gray treefrog) are associated with mobile genetic elements

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Cope's gray treefrog, Hyla chrysoscelis is composed of a complex of 5 cryptic species which occupy distinct geographical areas within the range of the currently recognized species and each species is defined by C-band patterns and the constitutional location of the 18S and 28S rRNA genes. In addition to the usual constitutional position of the ribosomal genes, there are extra sites detectable by FISH in all of the putative species of the complex. Many of the extra rRNA sites cannot be detected by NOR silver staining, indicating that they are not active, so they have to be analyzed using rRNA FISH probes. In over 200 individuals that have been analyzed so far by FISH, the location of the extra rRNA sites have been found to be unique to each individual. It has been hypothesized that mobile genetic elements of some type may be responsible for the polymorphisms found in the location of rRNA sequences in frogs and a number of other organisms, including plants. In order to test this hypothesis in gray treefrogs, a population with the constitutional rRNA gene position on the long arm of chromosome 8 (range east of the Appalachians from Virginia to Georgia) was chosen for study. Amplexed (mating) pairs were collected in the wild and placed in aquaria to complete egg laying. The parents and some of their progeny (tadpoles) were analyzed by FISH with a 28S rRNA probe. FISH analysis revealed that all of the tadpoles had the same constitutional rRNA gene locations as the parents, but they differed from their parents and each other in the location of the extra rRNA gene sites. This evidence supports the hypothesis that mobile elements may have an association with extra rRNA sites in H.chrysoscelis.