Insights into the genomic evolution of insects from cricket genomes

AbstractMost of our knowledge of insect genomes comes from Holometabolous species, which undergo complete metamorphosis and have genomes typically under 2 Gb with little signs of DNA methylation. In contrast, Hemimetabolous insects undergo the presumed ancestral process of incomplete metamorphosis, and have larger genomes with high levels of DNA methylation. Hemimetabolous species from the Orthopteran order (grasshoppers and crickets) have some of the largest known insect genomes. What drives the evolution of these unusual insect genome sizes, remains unknown. Here we report the sequencing, assembly and annotation of the 1.66-Gb genome of the Mediterranean field cricket Gryllus bimaculatus, and the annotation of the 1.60-Gb genome of the Hawaiian cricket Laupala kohalensis. We compare these two cricket genomes with those of 14 additional insects and find evidence that hemimetabolous genomes expanded due to transposable element activity. Based on the ratio of observed to expected CpG sites, we find higher conservation and stronger purifying selection of methylated genes than non-methylated genes. Finally, our analysis suggests an expansion of the pickpocket class V gene family in crickets, which we speculate might play a role in the evolution of cricket courtship, including their characteristic chirping.

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Cricket genomes: the genomes of future food

10.1101/2020.07.07.191841 ◽

2020 ◽

Cited By ~ 4

Author(s):

Guillem Ylla ◽

Taro Nakamura ◽

Takehiko Itoh ◽

Rei Kajitani ◽

Atsushi Toyoda ◽

...

Keyword(s):

Gene Family ◽

Courtship Behavior ◽

Purifying Selection ◽

Field Cricket ◽

Laboratory Research ◽

Human Consumption ◽

Class V ◽

Relevant Role ◽

Element Activity ◽

Multiple Health

AbstractCrickets are currently in focus as a possible source of animal protein for human consumption as an alternative to protein from vertebrate livestock. This practice could ease some of the challenges both of a worldwide growing population and of environmental issues. The two-spotted Mediterranean field cricket Gryllus bimaculatus has traditionally been consumed by humans in different parts of the world. Not only is this considered generally safe for human consumption, several studies also suggest that introducing crickets into one’s diet may confer multiple health benefits. Moreover, G. bimaculatus has been widely used as a laboratory research model for decades in multiple scientific fields including evolution, developmental biology, neurobiology, and regeneration. Here we report the sequencing, assembly and annotation of the G. bimaculatus genome, and the annotation of the genome of the Hawaiian cricket Laupala kohalensis. The comparison of these two cricket genomes with those of 14 additional insects supports the hypothesis that a relatively small ancestral insect genome expanded to large sizes in many hemimetabolous lineages due to transposable element activity. Based on the ratio of observed versus expected CpG sites (CpGo/e), we find higher conservation and stronger purifying selection of typically methylated genes than of non-methylated genes. Finally, our gene family expansion analysis reveals an expansion of the pickpocket class V gene family in the lineage leading to crickets, which we speculate might play a relevant role in cricket courtship behavior, including their characteristic chirping.

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