Nuclear Genome Size in Contrast to Sex Chromosome Number Variability in the Human Bed Bug, Cimex lectularius (Heteroptera: Cimicidae)

Rapid Targeted Assembly of the Proteome Reveals Evolutionary Variation of GC Content in Avian Lice

Nucleotide base composition plays an influential role in the molecular mechanisms involved in gene function, phenotype, and amino acid composition. GC content (proportion of guanine and cytosine in DNA sequences) shows a high level of variation within and among species. Many studies measure GC content in a small number of genes, which may not be representative of genome-wide GC variation. One challenge when assembling extensive genomic data sets for these studies is the significant amount of resources (monetary and computational) associated with data processing, and many bioinformatic tools have not been optimized for resource efficiency. Using a high-performance computing (HPC) cluster, we manipulated resources provided to the targeted gene assembly program, automated target restricted assembly method (aTRAM), to determine an optimum way to run the program to maximize resource use. Using our optimum assembly approach, we assembled and measured GC content of all of the protein-coding genes of a diverse group of parasitic feather lice. Of the 499 426 genes assembled across 57 species, feather lice were GC-poor (mean GC = 42.96%) with a significant amount of variation within and between species (GC range = 19.57%-73.33%). We found a significant correlation between GC content and standard deviation per taxon for overall GC and GC3, which could indicate selection for G and C nucleotides in some species. Phylogenetic signal of GC content was detected in both GC and GC3. This research provides a large-scale investigation of GC content in parasitic lice laying the foundation for understanding the basis of variation in base composition across species.

New estimates of genome size in Orthoptera and their evolutionary implications

Animal genomes vary widely in size, and much of their architecture and content remains poorly understood. Even among related groups, such as orders of insects, genomes may vary in size by orders of magnitude-for reasons unknown. The largest known insect genomes were repeatedly found in Orthoptera, e.g., Podisma pedestris (1C = 16.93 pg), Stethophyma grossum (1C = 18.48 pg) and Bryodemella holdereri (1C = 18.64 pg). While all these species belong to the suborder of Caelifera, the ensiferan Deracantha onos (1C = 19.60 pg) was recently found to have the largest genome. Here, we present new genome size estimates of 50 further species of Ensifera (superfamilies Gryllidea, Tettigoniidea) and Caelifera (Acrididae, Tetrigidae) based on flow cytometric measurements. We found that Bryodemella tuberculata (Caelifera: Acrididae) has the so far largest measured genome of all insects with 1C = 21.96 pg (21.48 gBp). Species of Orthoptera with 2n = 16 and 2n = 22 chromosomes have significantly larger genomes than species with other chromosome counts. Gryllidea genomes vary between 1C = 0.95 and 2.88 pg, and Tetrigidae between 1C = 2.18 and 2.41, while the genomes of all other studied Orthoptera range in size from 1C = 1.37 to 21.96 pg. Reconstructing ancestral genome sizes based on a phylogenetic tree of mitochondrial genomic data, we found genome size values of >15.84 pg only for the nodes of Bryodemella holdereri / B. tuberculata and Chrysochraon dispar / Euthystira brachyptera. The predicted values of ancestral genome sizes are 6.19 pg for Orthoptera, 5.37 pg for Ensifera, and 7.28 pg for Caelifera. The reasons for the large genomes in Orthoptera remain largely unknown, but a duplication or polyploidization seems unlikely as chromosome numbers do not differ much. Sequence-based genomic studies may shed light on the underlying evolutionary mechanisms.

Making the Genome Huge: The Case of Triatoma delpontei, a Triatominae Species with More than 50% of Its Genome Full of Satellite DNA

The genome of Triatoma delpontei Romaña & Abalos 1947 is the largest within Heteroptera, approximately two to three times greater than other evaluated Heteroptera genomes. Here, the repetitive fraction of the genome was determined and compared with its sister species Triatoma infestans Klug 1834, in order to shed light on the karyotypic and genomic evolution of these species. The T. delpontei repeatome analysis showed that the most abundant component in its genome is satellite DNA, which makes up more than half of the genome. The T. delpontei satellitome includes 160 satellite DNA families, most of them also present in T. infestans. In both species, only a few satellite DNA families are overrepresented on the genome. These families are the building blocks of the C-heterochromatic regions. Two of these satellite DNA families that form the heterochromatin are the same in both species. However, there are satellite DNA families highly amplified in the heterochromatin of one species that in the other species are in low abundance and located in the euchromatin. Therefore, the present results depicted the great impact of the satellite DNA sequences in the evolution of Triatominae genomes. Within this scenario, satellitome determination and analysis led to a hypothesis that explains how satDNA sequences have grown on T. delpontei to reach its huge genome size within true bugs.

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).

A new species of the genus Rhaphidosoma Amyot et Serville, 1843 (Heteroptera, Reduviidae), with data on its chromosome complement

A new species, Rhaphidosomapaganicum sp. nov. (Heteroptera: Reduviidae: Harpactorinae: Rhaphidosomatini), is described from the Dry Zone of Myanmar. It is the fifth species of Rhaphidosoma Amyot et Serville, 1843, known from the Oriental Region, and the first record of the genus for Myanmar and Indochina. The structure of the external and internal terminalia of the male and female is described and illustrated in detail. The completely inflated endosoma is described for the first time in reduviids. The complex structure of the ductus seminis is shown; it terminates with a voluminous seminal chamber which opens with a wide secondary gonopore and may be a place where spermatophores are formed. The new species is compared with all congeners from the Oriental Region and Western Asia. It is characterised by the absence of distinct tubercles on the abdominal tergites of the male, the presence only two long tubercles and small rounded ones on the abdominal tergites VII and VI, respectively, in the female, the presence of short fore wing vestiges which are completely hidden under longer fore wing vestiges, and other characters. In addition to the morphological description, an account is given of the male karyotype and the structure of testes of Rh.paganicum sp. nov. and another species of Harpactorinae, Polididusarmatissimus Stål, 1859 (tribe Harpactorini). It was found that Rh.paganicum sp. nov. has a karyotype comprising 12 pairs of autosomes and a multiple sex chromosome system (2n♂=24A+X₁X₂X₃Y), whereas P.armatissimus has a karyotype comprising five pairs of autosomes and a simple sex chromosome system (2n♂=10A+XY). The males of these species were found to have seven and nine follicles per testis, respectively. FISH mapping of 18S ribosomal DNA (major rDNA) revealed hybridisation signals on two of the four sex chromosomes (Y and one of the Xs) in Rh.paganicum sp. nov. and on the largest pair of autosomes in P.armatissimus. The presence of the canonical "insect" (TTAGG) _n telomeric repeat was detected in the chromosomes of both species. This is the first application of FISH in the tribe Raphidosomatini and in the genus Polididus Stål, 1858.

Peaceful revolution in genome size: polyploidy in the Nabidae (Heteroptera); autosomes and nuclear DNA content doubling

Genome size and the position of 18S ribosomal DNA (rDNA) were analysed in two Himacerus, eight Nabis and two Prostemma species from the family Nabidae using flow cytometry and fluorescence in situ hybrization techniques. The karyotypes of Nabis biformis and Nabis maoricus, each with 2n = 16 + XY, and Prostemma aeneicolle, with 2n = 26 + XY, were recorded for the first time. All the species displayed one or two 18S rDNA signals on the X chromosome and up to two signals on the Y chromosome. Several females exhibited two different types of X chromosome breakage, namely within or outside of the 18S rDNA region. Measurements of nuclear DNA content revealed significant differences between all three genera under study. Most notably, the nuclear DNA content of Himacerus species, with 2n = 32/36 + XY (2C = 9–10 pg), was double that of Nabis species, with 2n = 16 + XY (2C = 4–6 pg). Therefore, the previously rejected theory of an autosomal polyploidy event in the evolution of the genus Himacerus is strongly supported by the results of the present study and is now being resurrected.