New estimates of genome size in Orthoptera and their evolutionary implications

Abstract

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.

Species delimitation and molecular phylogeny of the grasshopper subfamily Gomphocerinae (Orthoptera: Acrididae) from Algeria based on mitochondrial and nuclear DNA markers

“…The phylogenetic position of Chorthippus marocanus aligns with the classification adopted in the Orthoptera Species File, which places it within the species group biguttulus (Linnaeus, 1758). The complex relationships within the Gomphocerini tribe have been previously observed and explained in various molecular studies (e.g., Dumas et al 2010;Nattier et al 2011;Vedenina and Mugue 2011;Hawlitschek et al 2017;Sukhikh et al 2019;Nolen et al 2020;Hawlitschek et al 2022Hawlitschek et al , 2023Gaugel et al 2023). Additionally, Hodjat and Saboori (2021) addressed the challenges and instability in the taxonomic classification of Gomphocerini species, attributing them to variations and plasticity in morphological characteristics, behaviour and acoustic communication influenced by environmental stress and hybridisation between populations.…”

“…Furthermore, Hawlitschek et al (2017) highlighted incomplete lineage sorting and hybridisation as major factors contributing to errors in species identification. Nonetheless, further taxonomic revision is necessary to establish a more detailed classification of this tribe (Bugrov et al 2006; Hawlitschek et al 2017, 2022).…”

A high-quality genome assembly of the ghost mothDruceiella hillmaniprovides new evidence of genome size augmentation in Hepialidae

“…This suggests that there may have been an ancestral largescale genome expansion within the family. Genome size expansions are less common than genome contractions and their evolutionary implications are often not clear [46][47][48][49] , even though they have been suggested to influence host range, reproductive fitness, and morphological traits in different taxa 46,[50][51][52] . Recently, genome size expansions in caddisflies (Trichoptera), the sister taxon of Lepidoptera, were related to more diverse and unstable habitats 53 .…”

Orthoptera-specific target enrichment (OR-TE) probes resolve relationships over broad phylogenetic scales

“…Nevertheless, the number of researchers who study the phylogeny of Orthoptera is small compared to those who study other major insect orders, and most of the molecular phylogenetic studies still rely on Sanger sequencing data or mitochondrial genome sequences. Genomic resources for developing phylogenomic tools have been largely lacking because orthopteran genomes are known to be the largest among insects 29,30 , and thus, very challenging to sequence and annotate. Although recent efforts to sequence orthopteran genomes have made great strides 31 , initiating a genome sequencing project for any orthopteran species remains challenging.…”