We studied the karyotypes of 8 dragonfly species originating from the Curonian Spit (the Baltic Sea, Russia) using C-banding and FISH with 18S rDNA and "insect" telomeric (TTAGG)n probes. Our results show that Leucorrhinia rubicunda, Libellula depressa, L. quadrimaculata, Orthetrum cancellatum, Sympetrum danae, and S. vulgatum from the family Libellulidae, as well as Cordulia aenea and Epitheca bimaculata from the family Corduliidae share 2n = 25 (24 + X) in males, with a minute pair of m-chromosomes being present in every karyotype except for that of C. aenea. Major rDNA clusters are located on one of the large pairs of autosomes in all the species. No hybridization signals were obtained by FISH with the (TTAGG)n probe in the examined species with the only exception of S. vulgatum. In this species, clear signals were detected at the ends of almost all chromosomes. This finding raises the possibility that in Odonata the canonical "insect" (TTAGG)n telomeric repeat is in fact present but in very low copy number and is consequently difficult to detect by in situ hybridization. We conclude that more work needs to be done to answer questions about the organization of telomeres in this very ancient and thus phylogenetically important insect order.
Keywords: (TTAGG)n; Corduliidae; FISH; Heterochromatin; Karyotype; Libellulidae; Odonata; rDNA.
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