General trends of chromosomal evolution in Aphidococca (Insecta, Homoptera, Aphidinea + Coccinea)

A comparative genomic analysis at the chromosomal-level reveals evolutionary patterns of aphid chromosomes

Genomic rearrangements are primary drivers of evolution, promoting biodiversity. Aphids, an agricultural pest with high species diversity, exhibit rapid chromosomal evolution and diverse karyotypes. These variations have been attributed to their unique holocentric chromosomes and parthenogenesis, though this hypothesis has faced scrutiny. In this study, we generated a chromosomal-level reference genome assembly of the celery aphid (Semiaphis heraclei) and conducted comparative genomic analysis, revealing varying chromosomal evolution rates among aphid lineages, positively correlating with species diversity. Aphid X chromosomes have undergone frequent intra-chromosomal recombination, while autosomes show accelerated inter-chromosomal recombination. Moreover, considering both inter- and intra-chromosomal rearrangements, the increased autosomal rearrangement rates may be common across the Aphidomorpha. We identified that the expansion of DNA transposable elements and short interspersed nuclear elements (SINEs), coupled with gene loss and duplication associated with karyotypic instability (such as RIF1, BRD8, DMC1, and TERT), may play crucial roles in aphid chromosomal evolution. Additionally, our analysis revealed that the mutation and expansion of detoxification gene families in S. heraclei may be a key factor in adapting to host plant chemical defenses. Our results provide new insights into chromosomal evolutionary patterns and detoxification gene families evolution in aphids, aiding the understanding of species diversity and adaptive evolution.

Gallophilous theory of cyclical parthenogenesis in aphids (Homoptera, Aphidinea)

The paper elaborates theoretical basis of the origin of aphid cyclical parthenogenesis in view of the original life of these insects in strobiloid galls on Picea spp. The period of gall opening is greatly extended in time, which prevents normal panmixia and creates a selective advantage for parthenogenetic reproduction. Migration of aphids to secondary host plants, on which closed galls never form, parthenogenetic reproduction on these plants, and the subsequent simultaneous return of "remigrants" to the main host plant make it possible to synchronize the development of the bisexual generation and achieve mass panmixia at the end of the life cycle only; it coincides with the end of summer growth shoots or the autumn end of the vegetation period as a whole. The evolutionary transition of aphids from conifers to angiosperms in the Cretaceous period in parallel meant the possibility of development in more spacious galls accommodating several consecutive parthenogenetic generations, the transition to viviparity and telescopic embryonization, significantly accelerating the propagation.

Two chromosome-level genome assemblies of galling aphids Slavum lentiscoides and Chaetogeoica ovagalla

Slavum lentiscoides and Chaetogeoica ovagalla are two aphid species from the subtribe Fordina of Fordini within the subfamily Eriosomatinae, and they produce galls on their primary host plants Pistacia. We assembled chromosome-level genomes of these two species using Nanopore long-read sequencing and Hi-C technology. A 332 Mb genome assembly of S. lentiscoides with a scaffold N50 of 19.77 Mb, including 11,747 genes, and a 289 Mb genome assembly of C. ovagalla with a scaffold N50 of 11.85 Mb, containing 14,492 genes, were obtained. The Benchmarking Universal Single-Copy Orthologs (BUSCO) benchmark of the two genome assemblies reached 93.7% (91.9% single-copy) and 97.0% (95.3% single-copy), respectively. The high-quality genome assemblies in our study provide valuable resources for future genomic research of galling aphids.

Karyotype and reproductive traits of the unique symbiotic mealybug Orbuspedummachinator G.-Z. (Homoptera, Coccinea)

The karyotype and reproductive features of Orbuspedummachinator Gavrilov-Zimin, 2017 (Pseudococcidae) were studied for the first time. Diploid chromosome number is 18 in females. Reproduction is probably bisexual, as indicated by the presence of characteristic Lecanoid heterochromatinization of the paternal set of chromosomes in embryonic cells of about 50% of the embryos studied. The female reproductive system has a pair of lateral oviducts merged into enlarged common oviduct; the spermatheca and accessory glands are connected to the common oviduct in its proximal part. Complete ovoviviparity occurs in ontogenesis.

Exploring chromosome evolution in 250 million year old groups of dragonflies and damselflies (Insecta:Odonata)

Using recently published chromosome-length genome assemblies of two damselfly species, Ischnura elegans and Platycnemis pennipes, and two dragonfly species, Pantala flavescens and Tanypteryx hageni, we demonstrate that the autosomes of Odonata have undergone few fission, fusion, or inversion events, despite 250 million years of separation. In the four genomes discussed here, our results show that all autosomes have a clear ortholog in the ancestral karyotype. Despite this clear chromosomal orthology, we demonstrate that different factors, including concentration of repeat dynamics, GC content, relative position on the chromosome, and the relative proportion of coding sequence all influence the density of syntenic blocks across chromosomes. However, these factors do not interact to influence synteny the same way in any two pairs of species, nor is any one factor retained in all four species. Furthermore, it was previously unknown whether the micro-chromosomes in Odonata are descended from one ancestral chromosome. Despite structural rearrangements, our evidence suggests that the micro-chromosomes in the sampled Odonata do indeed descend from an ancestral chromosome, and that the micro-chromosome in P. flavescens was lost through fusion with autosomes.

Ancient reproductive modes and criteria of multicellularity

It is demonstrated that the initial method of fertilization in animals (Metazoa), embryophyte plants (Embryophyta), most groups of multicellular oogamous algae, oogamous and pseudoogamous multicellular fungi was internal fertilization (in the broad meaning) in/on the body of a maternal organism. Accordingly, during the bisexual process, the initial method of formation of a daughter multicellular organism in animals was viviparity, and in embryophyte plants and most groups of oogamous multicellular algae - the germination of a zygote in/on the body of maternal organism. The reproductive criteria of multicellularity are proposed and discussed. In this regard, the multicellularity is considered to subdivide terminologically into three variants: 1) protonemal, the most simple, characteristic of multicellular prokaryotes, most groups of multicellular algae and gametophytes of some higher plants; 2) siphonoseptal, found among multicellular fungi, some groups of green and yellow-green algae; 3) embryogenic, most complicated, known in all animals (Metazoa), all sporophytes and some gametophytes of higher plants (Embryophyta), charophyte green algae Charophyceae s.s., oogamous species of green and brown algae, some genera of red algae. In addition to the well-known division of reproduction methods into sexual and asexual, it is proposed to divide the reproduction of multicellular organisms into monocytic (the emergence of a new organism from one cell sexually or asexually) and polycytic (fragmentation, longitudinal / transverse division or budding based on many cells of the body of the mother organism), since these two ways have different evolutionary and ontogenetic origins.

Uncovering the Male Presence in Parthenogenetic Marchalina hellenica (Hemiptera: Marchalinidae): Insights into Its mtDNA Divergence and Reproduction Strategy

Marchalina hellenica (Hemiptera: Marchalinidae), an endemic species in Greece and Turkey, is a major contributor to the annual honey production in its native range. However, in the areas that it invades, lacking natural enemies, it has detrimental effects on pine trees and potentially contributes to tree mortality. Although it was originally reported as thelytokous, males were later reported in Turkey and on several of the islands of Greece. To further disambiguate the exact parthenogenetic reproduction strategy of M. hellenica, we studied the emergence pattern of male individuals in Greece for two consecutive years (2021 and 2022). Furthermore, we examined the genetic variation among 15 geographically distant populations of M. hellenica in Greece using a mitochondrial DNA marker and compared the results with data from Turkey. The findings of this study document the existence of an additional M. hellenica population in its native range that repeatedly produces males, apart from the areas of Greece and Turkey in which they were initially reported, suggesting that males play a major, so far unknown role in the reproduction of this species. The populations in Greece and Turkey exhibited a strong genetic affinity, while human-aided dispersal seems to have obscured the genetic pattern acquired.

Evolutionary implications of new Postopsyllidiidae from mid-Cretaceous amber from Myanmar and sternorrhynchan nymphal conservatism

Nymphs of extinct sternorrhynchan hemipterans are extremely rare, although very important for understanding of evolutionary traits of these insects. A protopsyllidioid nymph, in mid-Cretaceous amber from Kachin, Myanmar, placed in the family Postopsyllidiidae, is the first nymph of this family to be found in the fossil. Postopsyllidiidae previously comprised the sole genus Postopsyllidium with a few species: P. rebeccae, P. grimaldii and P. burmaticum from Kachin amber (Cenomanian) and P. emilyae from Turonian amber of New Jersey. Here, we report a new genus and species of postopsyllid Megalophthallidion burmapteron gen. et sp. nov. (imago) and the first known nymph of the family ascribed to the same genus. An overview of the fossil record of sternorrhynchan nymphs, and the importance of this finding, unlocking a new and complementary window to understanding the evolutionary traits of Protopsyllidioidea and other Sternorrhyncha hemipterans are presented.

Aphids and Ants, Mutualistic Species, Share a Mariner Element with an Unusual Location on Aphid Chromosomes

Aphids (Hemiptera, Aphididae) are small phytophagous insects. The aim of this study was to determine if the mariner elements found in the ant genomes are also present in Aphis fabae and Aphis hederae genomes and the possible existence of horizontal transfer events. Aphids maintain a relationship of mutualism with the ants. The close contact between these insects could favour horizontal transfer events of transposable elements. Myrmar mariner element isolated from Myrmica ruginodis and Tapinoma ibericum ants have also been found in the two Aphis species: A. fabae and A. hederae (Afabmar-Mr and Ahedmar-Mr elements). Besides, Afabmar-Mr could be an active transposon. Myrmar-like elements are also present in other insect species as well as in one Crustacean species. The phylogenetic study carried out with all Myrmar-like elements suggests the existence of horizontal transfer. Most aphids have 2n = 8 with a XX-X0 sex determination system. Their complicated life cycle is mostly parthenogenetic with sexual individuals only in autumn. The production of X0 males, originated by XX females which produce only spermatozoa with one X chromosome, must necessarily occur through specialized cytogenetic and molecular mechanisms which are not entirely known. In both aphid species, the mariner elements are located on all chromosomes, including the X chromosomes. However, on the two X chromosomes, no positive signals are detected in their small DAPI-negative telomere regions. The rDNA sites are located, as in the majority of Aphids species, on one of the telomere regions of each X chromosome. The hybridization patterns obtained by double FISH demonstrate that Afabmar-Mr and Ahedmar-Mr elements do not hybridize at the rDNA sites of their host species. Possible causes for the absence of these transposons in the rDNA genes are discussed, probably related with the X chromosome biology.

Comparative analysis of chromosome numbers and sex chromosome systems in Paraneoptera (Insecta)

This article is part (the 4th article) of the themed issue (a monograph) "Aberrant cytogenetic and reproductive patterns in the evolution of Paraneoptera". The purpose of this article is to consider chromosome structure and evolution, chromosome numbers and sex chromosome systems, which all together constitute the chromosomal basis of reproduction and are essential for reproductive success. We are based on our own observations and literature data available for all major lineages of Paraneoptera including Zoraptera (angel insects), Copeognatha (=Psocoptera; bark lice), Parasita (=Phthiraptera s. str; true lice), Thysanoptera (thrips), Homoptera (scale insects, aphids, jumping plant-lice, whiteflies, and true hoppers), Heteroptera (true bugs), and Coleorrhyncha (moss bugs). Terminology, nomenclature, classification, and the study methods are given in the first paper of the issue (Gavrilov-Zimin et al. 2021).

Aberrant ontogeneses and life cycles in Paraneoptera

The paper is a third part of the themed issue "Aberrant cytogenetic and reproductive patterns in the evolution of Paraneoptera", prepared by a Russian-Bulgarian research team on the basis of long-term collaborative studies. This chapter reviews different peculiar aberrations in the ontogenesis of Paraneoptera, such as the appearance of the quiescent apodal and/or arostrate instars, exuviatrial, pupillarial and pseudopupillarial development, cyclic parthenogenesis, etc. The material and methods, terminology and the nomenclature of the used taxonomic names are listed in the first chapter of the issue (Gavrilov-Zimin et al. 2021).

Homologous series by Nikolai Vavilov in the phylogeny of Homoptera

The paper briefly discusses the most impressive examples of the Nikolai Vavilov's "Law of homologous series" in the evolution of one of the largest animal groups, homopterous insects, which comprise about 65,000 recent species in the world fauna. Different taxonomic and phylogenetic characters (morpho-anatomical, cytogenetic, reproductive and others) are considered at the taxonomic ranks of the order, suborder, superfamily and family.

Homologous series by Nikolai Vavilov in the phylogeny of Homoptera

The paper briefly discusses the most impressive examples of the Nikolai Vavilov's "Law of homologous series" in the evolution of one of the largest animal groups, homopterous insects, which comprise about 65,000 recent species in the world fauna. Different taxonomic and phylogenetic characters (morpho-anatomical, cytogenetic, reproductive and others) are considered at the taxonomic ranks of the order, suborder, superfamily and family.

Chromosomal and reproductive features of some Oriental and Australasian scale insects (Homoptera, Coccinea)

Fourteen species of scale insects from the families Margarodidae s.l., Pseudococcidae, Eriococcidae, and Coccidae were investigated for the first time in respect to karyotypes, genetic systems, modes of reproduction and general anatomy of the female reproductive system. One of the studied species, Steatococcus samaraius Morrison, 1927, showed hermaphroditic reproduction of the female-like specimens, the other species demonstrated bisexual reproduction with a peculiar "Lecanoid" heterochromatinization of the paternal set of chromosomes in male embryos or thelytocous parthenogenesis. Antonina parazonata Williams, 2004 and Saccharolecanium krugeri (Zehntner, 1897) are recorded here for the first time from Thailand, Antonina vietnamensis Williams, 2004 and Geococcus satellitum Williams, 2004 - for the first time from Laos.

Chromosome numbers in antlions (Myrmeleontidae) and owlflies (Ascalaphidae) (Insecta, Neuroptera)

A short review of main cytogenetic features of insects belonging to the sister neuropteran families Myrmeleontidae (antlions) and Ascalaphidae (owlflies) is presented, with a particular focus on their chromosome numbers and sex chromosome systems. Diploid male chromosome numbers are listed for 37 species, 21 genera from 9 subfamilies of the antlions as well as for seven species and five genera of the owlfly subfamily Ascalaphinae. The list includes data on five species whose karyotypes were studied in the present work. It is shown here that antlions and owlflies share a simple sex chromosome system XY/XX; a similar range of chromosome numbers, 2n = 14-26 and 2n = 18-22 respectively; and a peculiar distant pairing of sex chromosomes in male meiosis. Usually the karyotype is particularly stable within a genus but there are some exceptions in both families (in the genera Palpares and Libelloides respectively). The Myrmeleontidae and Ascalaphidae differ in their modal chromosome numbers. Most antlions exhibit 2n = 14 and 16, and Palparinae are the only subfamily characterized by higher numbers, 2n = 22, 24, and 26. The higher numbers, 2n = 20 and 22, are also found in owlflies. Since the Palparinae represent a basal phylogenetic lineage of the Myrmeleontidae, it is hypothesized that higher chromosome numbers are ancestral for antlions and were inherited from the common ancestor of Myrmeleontidae + Ascalaphidae. They were preserved in the Palparinae (Myrmeleontidae), but changed via chromosomal fusions toward lower numbers in other subfamilies.

Cytogenetic and taxonomic studies of some legless mealybugs (Homoptera, Coccinea, Pseudococcidae)

A new monotypic genus and species, Komodesia circuliplurimagen. et sp. n., from Flores Is. (Indonesia) and the new species, Antonina diversiglandulosasp. n., from Southern Thailand are described and illustrated. Chromosomes of these species and also the ones of Antonina purpurea Signoret, 1872 and Antonina thaiensis Takahashi, 1942 are studied for the first time: 2n = 30, 20, 12 and 22+Bs correspondingly; the male embryos of all four species demonstrate Lecanoid paternal heterochromatinization of one haploid set of chromosomes. The karyotypes of three widely distributed species, Antonina pretiosa Ferris, 1953, Antonina graminis (Maskell, 1897) and Chaetococcus bambusae (Maskell, 1893), are studied based on material from other regions in comparison with previously published data. Photographs of the karyotypes are provided for the first time for all seven species. The terminological problems connected with the identification and naming of the three scale insect genetic systems, Lecanoid, Comstockioid and Diaspidoid, are discussed.

Comparative cytogenetics of Auchenorrhyncha (Hemiptera, Homoptera): a review

A comprehensive review of cytogenetic features is provided for the large hemipteran suborder Auchenorrhyncha, which currently contains approximately 42,000 valid species. This review is based on the analysis of 819 species, 483 genera, and 31 families representing all presently recognized Auchenorrhyncha superfamilies, e.i. Cicadoidea (cicadas), Cercopoidea (spittle bugs), Membracoidea (leafhoppers and treehoppers), Myerslopioidea (ground-dwelling leafhoppers), and Fulgoroidea (planthoppers). History and present status of chromosome studies are described, as well as the structure of chromosomes, chromosome counts, trends and mechanisms of evolution of karyotypes and sex determining systems, their variation at different taxonomic levels and most characteristic (modal) states, occurrence of parthenogenesis, polyploidy, B-chromosomes and chromosome rearrangements, and methods used for cytogenetic analysis of Auchenorrhyncha.

Catalog of the adelgids of the world (Hemiptera, Adelgidae)

A taxonomic and nomenclatural Catalogue of the adelgids (Hemiptera: Adelgidae) is presented. Six family-group names are listed, five being synonyms of Adelgidae. Twenty-two genus-group names, of which nine are subjectively valid and in use, are presented with their type species, etymology, and grammatical gender. One hundred and six species-group names are listed, of which 70 are considered subjectively valid.

The marbled crayfish as a paradigm for saltational speciation by autopolyploidy and parthenogenesis in animals

The parthenogenetic all-female marbled crayfish is a novel research model and potent invader of freshwater ecosystems. It is a triploid descendant of the sexually reproducing slough crayfish, Procambarus fallax, but its taxonomic status has remained unsettled. By cross-breeding experiments and parentage analysis we show here that marbled crayfish and P. fallax are reproductively separated. Both crayfish copulate readily, suggesting that the reproductive barrier is set at the cytogenetic rather than the behavioural level. Analysis of complete mitochondrial genomes of marbled crayfish from laboratory lineages and wild populations demonstrates genetic identity and indicates a single origin. Flow cytometric comparison of DNA contents of haemocytes and analysis of nuclear microsatellite loci confirm triploidy and suggest autopolyploidisation as its cause. Global DNA methylation is significantly reduced in marbled crayfish implying the involvement of molecular epigenetic mechanisms in its origination. Morphologically, both crayfish are very similar but growth and fecundity are considerably larger in marbled crayfish, making it a different animal with superior fitness. These data and the high probability of a divergent future evolution of the marbled crayfish and P. fallax clusters suggest that marbled crayfish should be considered as an independent asexual species. Our findings also establish the P. fallax-marbled crayfish pair as a novel paradigm for rare chromosomal speciation by autopolyploidy and parthenogenesis in animals and for saltational evolution in general.