Vladimir E. Gokhman

Karyotypes of parasitic hymenoptera

Chromosomes of Hymenoptera.- Material and Methods.- Morphological Features of Karyotypes of Parasitic Hymenoptera.- Chromosomal Evolution of Parasitic Wasps.- Phylogenetic Implications of Karyotypic Characters of Parasitic Hymenoptera.- Chromosomal Analysis of Parasitic Wasps at Various Taxonomic Levels.

Morphometric analysis and taxonomic revision of Anisopteromalus Ruschka (Hymenoptera: Chalcidoidea: Pteromalidae) - an integrative approach.

We use an integrative taxonomic approach to revise the genus Anisopteromalus. In particular, we apply multivariate ratio analysis (MRA), a rather new statistical method based on principal component analysis (PCA) and linear discriminant analysis (LDA), to numerous body measurements and combine the data with those from our molecular analysis of Cytb and ITS2 genetic markers (on a subset of species) and all available published data on morphology, karyology, behaviour, host associations and geographic distribution. We demonstrate that the analysis of quantitative characters using MRA plays a major role for the integration of name‐bearing types and thus for the association of taxa with names. Six species are recognized, of which two are new: A. cornis Baur sp.n. and A. quinarius Gokhman & Baur sp.n. For Anisopteromalus calandrae (Howard), a well‐known, cosmopolitan parasitoid of stored‐product pests, we have selected a neotype to foster continuity and stability in the application of this important name. The species was sometimes confused with the related A. quinarius sp.n., another cosmopolitan species that is frequently encountered in similar environments. We also show that several species originally described or later put under Anisopteromalus actually belong to different genera: Cyrtoptyx camerunus (Risbec) comb.n.; Meraporus glaber (Szelényi) comb.n.; Dinarmus schwenkei (Roomi, Khan & Khan) comb.n. Neocatolaccus indicus Ayyar & Mani is confirmed as a junior synonym of Oxysychus sphenopterae (Ferrière) syn.n. and Anisopteromalus calandrae brasiliensis (Domenichini) stat.rev. must be considered as a valid but doubtful taxon.

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.

Comparative insect karyology: Current state and applications

The current state of the comparative insect karyology and the main applications of chromosomal analysis of insects are reviewed. The most important characteristics of insect karyotypes in mitosis and meiosis are considered. Karyological studies provide important information on the genetic structure, life cycles and ecological characteristics, evolution, taxonomy, and phylogeny of insects. Insects have two principal mechanisms of sex determination: more common mechanism is based on the presence of sex chromosomes, and another, on haplodiploidy. Karyotypic analysis allows a number of linkage groups as well as the primary sex ratio to be determined. Chromosomal rearrangement can be used for the ecological monitoring of various insect populations and for pest control. Although a full-scale use of karyotypic details for constructing phylogenies of large insect taxa (except for Diptera which have polygene chromosomes) is possible only in combination with other features, chromosomal characters are still very important for phylogenetic purposes because their evolution is more or less independent of the environment. Chromosomal analysis can be used to reveal and identify sibling species, as well as to identify immature phases of insects. Studies of insect chromosomes may reveal cases of hybridization between forms with different karyotypes. At present, squashed and air-dried preparations are used for studying insect chromosomes. Together with morphometric analysis, differential chromosome staining methods, such as C-and AgNOR-banding, fluorochrome staining, in situ hybridization (including chromosome painting), restriction banding, etc. are being used to detect and document karyotypic differences. An outline of trends and prospects of the comparative insect karyology is given.

Recombination, chromosome number and eusociality in the Hymenoptera

Extraordinarily high rates of recombination have been observed in some eusocial species. The most popular explanation is that increased recombination increases genetic variation among workers, which in turn increases colony performance, for example by increasing parasite resistance. However, support for the generality of higher recombination rates among eusocial organisms remains weak, due to low sample size and a lack of phylogenetic independence of observations. Recombination rate, although difficult to measure directly, is correlated with chromosome number. As predicted, several authors have noted that chromosome numbers are higher among the eusocial species of Hymenoptera (ants, bees and wasps). Here, we present a formal comparative analysis of karyotype data from 1567 species of Hymenoptera. Contrary to earlier studies, we find no evidence for an absolute difference between chromosome number in eusocial and solitary species of Hymenoptera. However, we find support for an increased rate of chromosome number change in eusocial taxa. We show that among eusocial taxa colony size is able to explain some of the variation in chromosome number: intermediate‐sized colonies have more chromosomes than those that are either very small or very large. However, we were unable to detect effects of a number of other colony characteristics predicted to affect recombination rate – including colony relatedness and caste number. Taken together, our results support the view that a eusocial lifestyle has led to variable selection pressure for increased recombination rates, but that identifying the factors contributing to this variable selection will require further theoretical and empirical effort.

Karyotypes of parasitic Hymenoptera: Diversity, evolution and taxonomic significance

Haploid chromosome numbers (n) of parasitic Hymenoptera (= traditional Parasitica + Chrysidoidea) vary from 2 to 23. However, this range can be subdivided into three intervals with n= 14–23 (less derived parasitic wasps, e.g., some Ichneumonidae and Braconidae as well as Gasteruptiidae), 8–13 (many other parasitic Hymenoptera) and 2–7 (Dryinidae, the majority of Chalcidoidea and some advanced Braconidae, e.g. Aphidiinae). The symmetric karyotype with a relatively high chromosome number (n= 14–17) and the prevalence of biarmed chromosomes must be considered as a groundplan feature of parasitic Hymenoptera. Independent reductions of chromosome numbers (n≤ 10–11) occurred in some groups of the superfamily Ichneumonoidea as well as in the common ancestor of the Proctotrupoidea sensu lato, Ceraphronoidea, Cynipoidea and Chalcidoidea. Further multiple decreases in chromosome numbers (n≤ 4–6) took place in some Braconidae, various lineages of the superfamily Chalcidoidea as well as in the family Dryinidae. Two main trends prevailed in the karyotype evolution of parasitic wasps: the reduction of chromosome numbers (mainly due to tandem fusions and less frequently due to centric ones) and karyotypic dissymmetrization (through an increase in size differentiation of chromosomes and/or in the share of acrocentrics in a chromosome set). Although karyotypic features of parasitic Hymenoptera can be used for solving taxonomic problems at various levels, this method is the most effective at the species level.

Implication of Chromosomal Analysis for the Taxonomy of Parasitic Wasps (Hymenoptera)

A review of principles for application of the morphology of the karyotype in the taxonomy of parasitic wasps is given. Specific character of the use of chromosomal characteristics at different taxonomic levels is determined. In the taxonomy of hymenopterans, the data on the morphology of the karyotype are the most important at the species level. By the taxonomic level and the degree of morphological isolation, closely related species of parasitic wasps, differing in the structure of chromosomal sets, can be subdivided into the following groups: well-distinguishable species; species with indistinct differences in the appearance (proper sibling species); morphologically identical populations; intrapopulation forms; specimens with spontaneous chromosomal mutations. It is suggested that chromosomal studies in the taxonomy of hymenopterans should be used as a method of express analysis of outdoor populations and laboratory strains of these insects.

Genomic and karyotypic variation in Drosophila parasitoids (Hymenoptera, Cynipoidea, Figitidae)

Abstract Drosophila melanogaster Meigen, 1830 has served as a model insect for over a century. Sequencing of the 11 additional Drosophila Fallen, 1823 species marks substantial progress in comparative genomics of this genus. By comparison, practically nothing is known about the genome size or genome sequences of parasitic wasps of Drosophila. Here, we present the first comparative analysis of genome size and karyotype structures of Drosophila parasitoids of the Leptopilina Förster, 1869 and Ganaspis Förster, 1869 species. The gametic genome size of Ganaspis xanthopoda (Ashmead, 1896) is larger than those of the three Leptopilina species studied. The genome sizes of all parasitic wasps studied here are also larger than those known for all Drosophila species. Surprisingly, genome sizes of these Drosophila parasitoids exceed the average value known for all previously studied Hymenoptera. The haploid chromosome number of both Leptopilina heterotoma (Thomson, 1862) and Leptopilina victoriae Nordlander, 1980 is ten. A chromosomal fusion appears to have produced a distinct karyotype for Leptopilina boulardi (Barbotin, Carton et Keiner-Pillault, 1979)(n = 9), whose genome size is smaller than that of wasps of the Leptopilina heterotoma clade. Like Leptopilina boulardi, the haploid chromosome number for Ganaspis xanthopoda is also nine. Our studies reveal a positive, but non linear, correlation between the genome size and total chromosome length in Drosophila parasitoids. These Drosophila parasitoids differ widely in their host range, and utilize different infection strategies to overcome host defense. Their comparative genomics, in relation to their exceptionally well-characterized hosts, will prove to be valuable for understanding the molecular basis of the host-parasite arms race and how such mechanisms shape the genetic structures of insectcommunities.

Results and prospects of the chromosomal study of the main groups of economically important Chalcidoidea (Hymenoptera)

A brief review of the results of the chromosomal study of the main economically important groups of parasitoids of the superfamily Chalcidoidea is presented. Methods of chromosomal analysis can be used to study the species complexes within taxonomically complicated groups, to identify adult and immature chalcids to species, to identify insects in laboratory stocks and mass-rearing cultures, to study sex ratios of immature stages, and to reveal specific sex-ratio distorters with chromosomal localization. There are reasons to believe that chromosomal analysis will be successfully used in the future for studying not only economically significant chalcids but also other practically important groups of parasitoid Hymenoptera.

New data on chromosomes of Chalcidoidea (Hymenoptera)

Karyotypes of twelve species of chalcidoid wasps from five families were studied for the first time: Baryscapus endemus and B. galactopus (2n = 12), Entedon parvicalcar and E. procioni (n = 6), and E. sparetus (2n = 12; all Eulophidae); Sycophila submutica (2n =16; Eurytomidae); Cerchysius subplanus (n = 11 and 2n = 22; Encyrtidae); Pteromalus cioni (2n =10; Pteromalidae); Pseudotorymus sp., Torymus microstigma, T. rubi, and Torymus sp. (all with 2n = 12; Torymidae). Various aspects of chromosomal diversity of Chalcidoidea are discussed.