Genomes of numerous diploid plant and animal species possess traces of interspecific crosses, and many researches consider them as support for homoploid hybrid speciation (HHS), a process by which a new reproductively isolated species arises through hybridization and combination of parts of the parental genomes, but without an increase in ploidy. However, convincing evidence for a creative role of hybridization in the origin of reproductive isolation between hybrid and parental forms is extremely limited. Here, through studying Agrodiaetus butterflies, we provide proof of a previously unknown mode of HHS based on the formation of post-zygotic reproductive isolation via hybridization of chromosomally divergent parental species and subsequent fixation of a novel combination of chromosome fusions/fissions in hybrid descendants. We show that meiotic segregation, operating in the hybrid lineage, resulted in the formation of a new diploid genome, drastically rearranged in terms of chromosome number. We also demonstrate that during the heterozygous stage of the hybrid species formation, recombination was limited between rearranged chromosomes of different parental origin, representing evidence that the reproductive isolation was a direct consequence of hybridization.

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.

The species-rich subgenus Polyommatus (Agrodiaetus) has become one of the best studied groups of Palearctic blue butterflies (Lepidoptera, Lycaenidae). However, the identity and phylogenetic position of some rare taxa from Iran have remained unclear. An enigmatic, recently described Central Iranian species Polyommatus (Agrodiaetus) shirkuhensis ten Hagen et Eckweiler, 2001 has been considered as a taxon closely related either to Polyommatus (Agrodiaetus) eckweileri ten Hagen, 1998 or to Polyommatus (Agrodiaetus) baltazardi (de Lesse, 1962). Polyommatus (Agrodiaetus) baltazardi, in its turn, was treated as a taxon close to Iranian-Pakistani Polyommatus (Agrodiaetus) bogra Evans, 1932. Here we used a combination of molecular and chromosomal markers to show that none of these hypotheses was true. Instead, Polyommatus (Agrodiaetus) shirkuhensis was recovered as a member of a species group close to Polyommatus (Agrodiaetus) cyaneus (Staudinger, 1899). From genetically closest species, Polyommatus (Agrodiaetus) kermansis (de Lesse, 1962), Polyommatus (Agrodiaetus) cyaneus and Polyommatus (Agrodiaetus) sennanensis (de Lesse, 1959), it differs by the wing coloration. From morphologically similar Polyommatus (Agrodiaetus) mofidii (de Lesse, 1963) and Polyommatus (Agrodiaetus) sorkhensis Eckweiler, 2003, it differs by its chromosome number, n=21. Polyommatus (Agrodiaetus) bogra and Polyommatus (Agrodiaetus) baltazardi were found to be members of two different species groups and, thus, are not closely related.

All Odonata species studied to date using fluorescence in situ hybridization (FISH) belong to the dragonfly (Anisoptera) families Corduliidae and Libellulidae. It was shown that 18S rRNA gene 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 and 18S rRNA gene 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 former 18S location 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.