Chromosomal analysis of eight species of dragonflies (Anisoptera) and damselflies (Zygoptera) using conventional cytogenetics and fluorescence in situ hybridization: Insights into the karyotype evolution of the ancient insect order Odonata

All Odonata species studied to date using fluorescence in situ hybridization (FISH) belong to the dragonfly (Anisoptera) families Corduliidae and Libellulidae. It was shown that18S rRNAgene loci locate on one of the largest pairs of autosomes in every species, whereas the insect telomere motif (TTAGG)(n)is absent in all but one species. For better understanding the chromosomal organization and evolution of Odonata, we used C-banding and FISH to study the karyotypes and map TTAGG sequences and major rRNA loci on chromosomes of three more dragonfly species from the families Corduliidae, Libellulidae, and Aeshnidae. Moreover, we obtained the first FISH-data on the suborder Zygoptera (damselflies) by analyzing five species of the families Coenagrionidae and Calopterygidae. We showed that all studied dragonfly species had 2n = 24A + X. The same karyotype was observed in the damselfly family Coenagrionidae, whereas in species of the Calopterygidae, the karyotype 2n = 26A + X was found. Both dragonfly and damselfly species had a pair of m-chromosomes; constitutive heterochromatin tended to be concentrated in the terminal regions of their chromosomes. The use of (TTAGG)(n)and18S rRNAgene probes in dual-color FISH did not generate (TTAGG)(n)fluorescent signals in any species; major rRNA clusters were revealed on one of the largest pairs of autosomes in all Anisoptera species but on m-chromosomes in all Zygoptera species. Our results suggest that the former18Slocation pattern was ancestral in the Odonata and the latter pattern had an ancient origin and could arise in a common ancestor of the damselfly superfamilies Calopterygoidea and Coenagrionoidea.

Automated summary

Research on Odonata species using FISH revealed differences in chromosomal organization between dragonflies and damselflies, with dragonflies having a consistent 2n = 24A + X karyotype while damselflies show variation with a different karyotype. The presence of a pair of m-chromosomes and the distribution of major rRNA clusters showed distinct patterns between the two groups of insects.