Boris A. Anokhin

Homoploid hybrid speciation and genome evolution via chromosome sorting

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.

Distribution of 18S rDNA sites and absence of the canonical TTAGG insect telomeric repeat in parasitoid Hymenoptera

Karyotypes of six species belonging to three main clades of parasitoid Hymenoptera, the superfamilies Ichneumonoidea (Ichneumonidae: Ichneumon amphibolus), Cynipoidea (Cynipidae: Diplolepis rosae) and Chalcidoidea (Eurytomidae: Eurytoma robusta, Eu. serratulae and Eu. compressa, and Torymidae: Torymus bedeguaris) were studied using FISH with 18S rDNA and telomeric (TTAGG)n probes. Haploid karyotypes of D. rosae, Eu. robusta and Eu. serratulae carried the only 18S rDNA hybridization signal, whereas those of I. amphibolus and Eu. compressa carried three and two rDNA clusters respectively. In addition, three rDNA sites were visualized in the aneuploid female of T. bedeguaris. The number of rDNA clusters in parasitoid Hymenoptera generally correlates to the chromosome number. Apart from the overwhelming majority of the studied species of aculeate Hymenoptera, no hybridization signals were obtained from FISH with the telomeric (TTAGG)n probe in the examined parasitoid species. These data suggest absence of the canonical (TTAGG)n insect telomeric motif in the Ichneumonoidea, Cynipoidea and Chalcidoidea, and perhaps in parasitoid Hymenoptera in general.

Ribosomal DNA clusters and telomeric (TTAGG)n repeats in blue butterflies (Lepidoptera, Lycaenidae) with low and high chromosome numbers

Abstract Ribosomal DNA clusters and telomeric repeats are important parts of eukaryotic genome. However, little is known about their organization and localization in karyotypes of organisms with holocentric chromosomes. Here we present first cytogenetic study of these molecular structures in seven blue butterflies of the genus Polyommatus Latreille, 1804 with low and high chromosome numbers (from n=10 to n=ca.108) using fluorescence in situ hybridization (FISH) with 18S rDNA and (TTAGG)n telomeric probes. FISH with the 18S rDNA probe showed the presence of two different variants of the location of major rDNA clusters in Polyommatus species: with one or two rDNA-carrying chromosomes in haploid karyotype. We discuss evolutionary trends and possible mechanisms of changes in the number of ribosomal clusters. We also demonstrate that Polyommatus species have the classical insect (TTAGG)n telomere organization. This chromosome end protection mechanism probably originated de novo in small chromosomes that evolved via fragmentations.

The genus Monocoryne (Hydrozoa, Capitata): Peculiarities of morphology, species composition, biology and distribution

A revision of the genus Monocoryne was undertaken following analysis of peculiarities noted in earlier descriptions of the nominal species. Type specimens of Monocoryne gigantea from northern Norway and Monocoryne minor from South Africa were examined. In addition, non-type material from the Arctic Ocean, Antarctic Seas and the Kuril Islands was studied, and descriptions of species from Alaska and the Canadian Archipelago were investigated. A new diagnosis of the genus Monocoryne, provided here, was a necessary outcome of these studies. Most importantly, hydroids (in species of the genus) are colonial or solitary which differ from Bonnevies original diagnosis. The collection of solitary polyps is a result of the tenuous nature of the colonies, which tend to fall to pieces. Species of Monocoryne are found in Arctic, Antarctic and temperate waters of the northern and southern hemispheres, and the genus may thus be regarded as bipolar. Although recognized species of Monocoryne are quite similar morphologically, four of them are recognized here to be valid based on current evidence. This conclusion is also supported by their distribution patterns.

Karyotype stability in the family Issidae (Hemiptera, Auchenorrhyncha) revealed by chromosome techniques and FISH with telomeric (TTAGG)n and 18S rDNA probes

Abstract We report several chromosomal traits in 11 species from 8 genera of the planthopper family Issidae, the tribes Issini, Parahiraciini and Hemisphaeriini. All species present a 2n = 27, X(0) chromosome complement known to be ancestral for the family. The karyotype is conserved in structure and consists of a pair of very large autosomes; the remaining chromosomes gradually decrease in size and the X chromosome is one of the smallest in the complement. For selected species, analyses based on C-, AgNOR- and CMA3-banding techniques were also carried out. By fluorescence in situ hybridization, the (TTAGG)n probe identified telomeres in all species, and the major rDNA loci were detected on the largest pair of autosomes. In most species, ribosomal loci were found in an interstitial position while in two species they were located in telomeric regions suggesting that chromosomal rearrangements involving the rDNA segments occurred in the evolution of the family Issidae. Furthermore, for 8 species the number of testicular follicles is provided for the first time.

Cnidarian fauna of relict Lakes Baikal, Biwa and Khubsugul

In relict Lakes Baikal, Biwa and Khubsugul three orders: Hydrida, Athecata and Limnomedusa (?) of the class Hydrozoa were found. In Lake Baikal, only representatives of Hydrida, such as Pelmathohydra baikalensis (endemic of Lake Baikal), P. oligactis and Hydracircumcincta were found (the last two species had not been found there before. Recent studies of the phylum Cnidaria in Lake Biwa showed the presence of Pelmatohydra oligactis and a representative of the family Clavidae which has been treated as a new species, Pachycordyle kubotai. In Lake Khubsugul a single representative of Hydrida has been found so far which is suggested to represent a new species of Pelmatohydra. According to techniques described earlier air-dried chromosome slides were prepared. The karyotype of P. kubotai were studied using conventional chromosome staining (by 6–10% Giemsa in the Sørensen’s buffer, pH 6.8), whereas karyotype of P. baikalensis was studied using conventional and C-banding techniques. C-banding to reveal highly repeated DNA followed the protocol by Sumner (1972).

Characterization of C-heterochromatin in four species of Hydrozoa (Cnidaria) by sequence specific fluorochromes Chromomycin A3 and DAPI

Abstract The karyotypes of Pelmatohydra oligactis (Pallas, 1766), Hydra vulgaris Pallas, 1766, Hydra circumcincta Schulze, 1914 (Hydrida, Hydridae) and Pachycordyle kubotai Stepanjants, Timoshkin, Anokhin, Napara, 2000 (Athecata, Clavidae) have been studied for the first time by using the fluorochromes DAPI, and CMA3. In all the species C-heterochromatic regions were stained brightly with DAPI, indicating that constitutive heterochromatin associated with centromeres or NORs is A-T-rich. CMA3 staining showed exceptionally rare G-C-rich clusters associated with NORs.

Cytogenetic Characterization of Eight Odonata Species Originating from the Curonian Spit (the Baltic Sea, Russia) Using C-Banding and FISH with 18S rDNA and Telomeric (TTAGG)n Probes

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.

Cytogenetic study on antlions (Neuroptera, Myrmeleontidae): first data on telomere structure and rDNA location

Abstract Myrmeleontidae, commonly known as “antlions”, are the most diverse family of the insect order Neuroptera, with over 1700 described species (in 191 genera) of which 37 species (in 21 genera) have so far been studied in respect to standard karyotypes. In the present paper we provide first data on the occurrence of the “insect-type” telomeric repeat (TTAGG)n and location of 18S rDNA clusters in the antlion karyotypes studied using fluorescence in situ hybridization (FISH). We show that males of Palpares libelluloides (Linnaeus, 1764) (Palparinae), Acanthaclisis occitanica (Villers, 1789) (Acanthaclisinae) and Distoleon tetragrammicus (Fabricius, 1798) (Nemoleontinae) have rDNA clusters on a large bivalent, two last species having an additional rDNA cluster on one of the sex chromosomes, most probably the X. (TTAGG)n - containing telomeres are clearly characteristic of Palpares libelluloides and Acanthaclisis occitanica; the presence of this telomeric motif in Distoleon tetragrammicus is questionable. In addition, we detected the presence of the (TTAGG)n telomeric repeat in Libelloides macaronius (Scopoli, 1763) from the family Ascalaphidae (owlflies), a sister group to the Myrmeleontidae. We presume that the “insect” motif (TTAGG)n was present in a common ancestor of the families Ascalaphidae and Myrmeleontidae within the neuropteran suborder Myrmeleontiformia.