Comprehensive analysis of the Xya riparia genome uncovers the dominance of DNA transposons, LTR/Gypsy elements, and their evolutionary dynamics.

Transposable elements (TEs) are DNA sequences that can move or replicate within a genome, and their study has become increasingly important in understanding genome evolution and function. The Tridactylidae family, including Xya riparia (pygmy mole cricket), harbors a variety of transposable elements (TEs) that have been insufficiently investigated. Further research is required to fully understand their diversity and evolutionary characteristics. Hence, we conducted a comprehensive repeatome analysis of X. riparia species using the chromosome-level assembled genome. The study aimed to comprehensively analyze the abundance, distribution, and age of transposable elements (TEs) in the genome. The results indicated that the genome was 1.67 Gb, with 731.63 Mb of repetitive sequences, comprising 27% of Class II (443.25 Mb), 16% of Class I (268.45 Mb), and 1% of unknown TEs (19.92 Mb). The study found that DNA transposons dominate the genome, accounting for approximately 60% of the total repeat size, with retrotransposons and unknown elements accounting for 37% and 3% of the genome, respectively. The members of the Gypsy superfamily were the most abundant amongst retrotransposons, accounting for 63% of them. The transposable superfamilies (LTR/Gypsy, DNA/nMITE, DNA/hAT, and DNA/Helitron) collectively constituted almost 70% of the total repeat size of all six chromosomes. The study further unveiled a significant linear correlation (Pearson correlation: r = 0.99, p-value = 0.00003) between the size of the chromosomes and the repetitive sequences. The average age of DNA transposon and retrotransposon insertions ranges from 25 My (million years) to 5 My. The satellitome analysis discovered 13 satellite DNA families that comprise about 0.15% of the entire genome. In addition, the transcriptional analysis of TEs found that DNA transposons were more transcriptionally active than retrotransposons. Overall, the study suggests that the genome of X. riparia is complex, characterized by a substantial portion of repetitive elements. These findings not only enhance our understanding of TE evolution within the Tridactylidae family but also provide a foundation for future investigations into the genomic intricacies of related species.

A Chromosome-Level Genome Assembly and Annotation for the Oecanthus rufescens (Orthoptera: Oecanthidae).

Oecanthus is a genus of cricket known for its distinctive chirping and distributed across major zoogeographical regions worldwide. This study focuses on Oecanthus rufescens, and conducts a comprehensive examination of its genome through genome sequencing technologies and bioinformatic analysis. A high-quality chromosome-level genome of O. rufescens was successfully obtained, revealing significant features of its genome structure. The genome size is 877.9 Mb, comprising ten pseudo-chromosomes and 70 other sequences, with a GC content of 41.38% and an N50 value of 157,110,771 bp, indicating a high level of continuity. BUSCO assessment results demonstrate that the genome's integrity and quality are high (of which 96.8% are single-copy and 1.6% are duplicated). Comprehensive genome annotation was also performed, identifying approximately 310 Mb of repetitive sequences, accounting for 35.3% of the total genome sequence, and discovering 15,481 tRNA genes, 4,082 rRNA genes, and 1,212 other noncoding genes. Furthermore, 15,031 protein-coding genes were identified, with BUSCO assessment results showing that 98.4% (of which 96.3% are single-copy and 1.6% are duplicated) of the genes were annotated.

Repetitive element expansions contribute to genome size gigantism in Pamphagidae: A comparative study (Orthoptera, Acridoidea).

Pamphagidae is a family of Acridoidea that inhabits the desert steppes of Eurasia and Africa. This study employed flow cytometry to estimate the genome size of eight species in the Pamphagidae. The results indicate that the genome size of the eight species ranged from 13.88 pg to 14.66 pg, with an average of 14.26 pg. This is the largest average genome size recorded for the Orthoptera families, as well as for the entire Insecta. Furthermore, the study explored the role of repetitive sequences in the genome, including their evolutionary dynamics and activity, using low-coverage next-generation sequencing data. The genome is composed of 14 different types of repetitive sequences, which collectively make up between 59.9% and 68.17% of the total genome. The Pamphagidae family displays high levels of transposable element (TE) activity, with the number of TEs increasing and accumulating since the family's emergence. The study found that the types of repetitive sequences contributing to the TE outburst events are similar across species. Additionally, the study identified unique repetitive elements for each species. The differences in repetitive sequences among the eight Pamphagidae species correspond to their phylogenetic relationships. The study sheds new light on genome gigantism in the Pamphagidae and provides insight into the correlation between genome size and repetitive sequences within the family.

Transposable element expansion and low-level piRNA silencing in grasshoppers may cause genome gigantism.

BACKGROUND: Transposable elements (TEs) have been likened to parasites in the genome that reproduce and move ceaselessly in the host, continuously enlarging the host genome. However, the Piwi-interacting RNA (piRNA) pathway defends animal genomes against the harmful consequences of TE invasion by imposing small-RNA-mediated silencing. Here we compare the TE activity of two grasshopper species with different genome sizes in Acrididae (Locusta migratoria manilensis♀1C = 6.60 pg, Angaracris rhodopa♀1C = 16.36 pg) to ascertain the influence of piRNAs. RESULTS: We discovered that repetitive sequences accounted for 74.56% of the genome in A. rhodopa, more than 56.83% in L. migratoria, and the large-genome grasshopper contained a higher TEs proportions. The comparative analysis revealed that 41 TEs (copy number > 500) were shared in both species. The two species exhibited distinct "landscapes" of TE divergence. The TEs outbreaks in the small-genome grasshopper occurred at more ancient times, while the large-genome grasshopper maintains active transposition events in the recent past. Evolutionary history studies on TEs suggest that TEs may be subject to different dynamics and resistances in these two species. We found that TE transcript abundance was higher in the large-genome grasshopper and the TE-derived piRNAs abundance was lower than in the small-genome grasshopper. In addition, we found that the piRNA methylase HENMT, which is underexpressed in the large-genome grasshopper, impedes the piRNA silencing to a lower level. CONCLUSIONS: Our study revealed that the abundance of piRNAs is lower in the gigantic genome grasshopper than in the small genome grasshopper. In addition, the key gene HENMT in the piRNA biogenesis pathway (Ping-Pong cycle) in the gigantic genome grasshopper is underexpressed. We hypothesize that low-level piRNA silencing unbalances the original positive correlation between TEs and piRNAs, and triggers TEs to proliferate out of control, which may be one of the reasons for the gigantism of grasshopper genomes.

The Evolutionary Patterns of Genome Size in Ensifera (Insecta: Orthoptera).

Genomic size variation has long been a focus for biologists. However, due to the lack of genome size data, the mechanisms behind this variation and the biological significance of insect genome size are rarely studied systematically. The detailed taxonomy and phylogeny of the Ensifera, as well as the extensive documentation concerning their morphological, ecological, behavioral, and distributional characteristics, make them a strong model for studying the important scientific problem of genome size variation. However, data on the genome size of Ensifera are rather sparse. In our study, we used flow cytometry to determine the genome size of 32 species of Ensifera, the smallest one being only 1C = 0.952 pg with the largest species up to 1C = 19.135 pg, representing a 20-fold range. This provides a broader blueprint for the genome size variation of Orthoptera than was previously available. We also completed the assembly of nine mitochondrial genomes and combined mitochondrial genome data from public databases to construct phylogenetic trees containing 32 species of Ensifera and three outgroups. Based on these inferred phylogenetic trees, we detected the phylogenetic signal of genome size variation in Ensifera and found that it was strong in both males and females. Phylogenetic comparative analyses revealed that there were no correlations between genome size and body size or flight ability in Tettigoniidae. Reconstruction of ancestral genome size revealed that the genome size of Ensifera evolved in a complex pattern, in which the genome size of the grylloid clade tended to decrease while that of the non-grylloid clade expanded significantly albeit with fluctuations. However, the evolutionary mechanisms underlying variation of genome size in Ensifera are still unknown.

Genome Size of 17 Species From Caelifera (Orthoptera) and Determination of Internal Standards With Very Large Genome Size in Insecta.

Comparative studies of insect genome size show that Orthoptera is a unique group of Insecta with a significantly enlarged genome. To determine a suitable internal standard for a large genome and to compare the effects of different internal standards on estimates of genome size, we used four internal standards to estimate nuclear DNA content in nine insect species with large genomes. The results showed that the combination of two internal standards, Locusta migratoria (♂1C = 6.20 pg, ♀1C = 6.60 pg) and Periplaneta americana♂ (1C = 3.41 pg), was suitable for estimating large genome of Caelifera by flow cytometry. Using these two internal standards, we estimated the genome sizes of 17 species of Caelifera (12 genera in Acrididae, 2 genera in Pamphagidae, 1 genus in Pyrgomorphidae) using flow cytometry. Genomes ranged from 6.57 pg (Shirakiacris shirakii) to 18.64 pg (Bryodemella holdereri), the largest described in insects to date. These species showed significant genomic dimorphism based on sex: females had a 0.56 pg larger genome than males on average, which might be due to the sex chromosome determinism mechanism of X0(♂)/XX(♀). To test the results obtained by flow cytometry, we used k-mers of Illumina sequencing data to gauge the C-value of Calliptamus abbreviatus and Haplotropis brunneriana. The results of the two methods are slightly different. Genomes were estimated to be about 0.28 and 0.26 pg smaller, respectively, than the flow cytometry values. Furthermore, we also reconstructed the evolutionary relationships of these taxa and discuss the genome size evolution in a phylogenetic framework.

MtOrt: an empirical mitochondrial amino acid substitution model for evolutionary studies of Orthoptera insects.

BACKGROUND: Amino acid substitution models play an important role in inferring phylogenies from proteins. Although different amino acid substitution models have been proposed, only a few were estimated from mitochondrial protein sequences for specific taxa such as the mtArt model for Arthropoda. The increasing of mitochondrial genome data from broad Orthoptera taxa provides an opportunity to estimate the Orthoptera-specific mitochondrial amino acid empirical model. RESULTS: We sequenced complete mitochondrial genomes of 54 Orthoptera species, and estimated an amino acid substitution model (named mtOrt) by maximum likelihood method based on the 283 complete mitochondrial genomes available currently. The results indicated that there are obvious differences between mtOrt and the existing models, and the new model can better fit the Orthoptera mitochondrial protein datasets. Moreover, topologies of trees constructed using mtOrt and existing models are frequently different. MtOrt does indeed have an impact on likelihood improvement as well as tree topologies. The comparisons between the topologies of trees constructed using mtOrt and existing models show that the new model outperforms the existing models in inferring phylogenies from Orthoptera mitochondrial protein data. CONCLUSIONS: The new mitochondrial amino acid substitution model of Orthoptera shows obvious differences from the existing models, and outperforms the existing models in inferring phylogenies from Orthoptera mitochondrial protein sequences.