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

Abstract

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.

Dissecting cricket genomes for the advancement of entomology and entomophagy

“…Consistently, in flatworms and copepods, a strong association between genome size and body size has been reported (Gregory et al 2000). However, a study that examined genome size and body size in Tettigoniidae species did not find a significant positive correlation between them, but it may need to be tested more rigorously with a larger sample size (Yuan et al 2021). It would be interesting to investigate the mechanisms that allow for variation in genome size.…”

“…The genome size of Gryllidea ranges from 1.55 Gbp in Hadenoecus subterraneus to 2.25 Gbp in Gryllus pennsylvanicus, which is a relatively small subset of Orthoptera. Indeed, several lines of comprehensive studies also have suggested that genome sizes of insects in Gryllidea are in the minimum range for orthopterans (Hanrahan and Johnston 2011;Yuan et al 2021). Considering that the median genome size of insects is 518.…”

“…Finally, we discuss how the diversity of orthopteran genome size can be involved in biology and evolution. A study that brings a phylogenetic view to the comparison of genome sizes in orthopteran insects suggests that the genome size of Tettigoniidae is expanding while that of Gryllidae is shrinking (Yuan et al 2021). As shown in Fig.…”

“…1, these two clades are the species-richest clade in Ensifera, indicating extensive species divergence. Yuan et al have proposed the following scenario for the divergence of Tettigoniidae and Gryllidae in relation to their genome size (Yuan et al 2021). The increase in the number of species in the Tettigoniidae may be due to events such as gene duplications and transposon insertions, which are also responsible for genome size expansion, causing beneficial mutations that result in the acquisition of new ecological niches (Dufresne and Jeffery 2011).…”

Chromosome‐level genome assembly for the horned‐gall aphid provides insights into interactions between gall‐making insect and its host plant

“…This observation strongly supports that chrX1, chrX2 and chrX3 are the sex chromosomes and the karyotype of S . chinensis is XX+X (Yuan et al, 2021 ).…”