Travnicek, P. | bioRxiv Science

bioRxiv2022

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 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 seems unlikely as chromosome numbers do not differ. Sequence-based genomic studies may shed light on the underlying evolutionary mechanisms.

genomics↗

bioRxiv2020

Partial endoreplication stimulates diversification in the species-richest lineage of orchids

Some of the most burning questions in biology in recent years concern differential diversification along the tree of life and its causes. Among others, it could be triggered by the evolution of novel phenotypes accelerating diversification in lineages that bear them. In the Pleurothallidinae, the most species-rich subtribe of plants on Earth with 46 genera and [~]5,500 species, we constructed a completely new phylogeny and mapped on to it the type of endoreplication intending to trace how the phenomenon of partial endoreplication, which is unique to orchids, affects the differential diversification of lineages. We have used NGS based target enrichment HybSeq approach for the reconstruction of the phylogeny and the flow cytometry to estimate the type of endoreplication. The BAMM and BiSSE analyses have been used to assess diversification rates and to trace the phenotype changes. We have found that three of six changes in diversification rates are associated with changes in the endoreplication type and the clades bearing taxa with partial endoreplication showed higher net diversification rates. Our results demonstrate that multiple evolution of partial endoreplication within the subtribe considerably shapes the patterns of diversity and that partial endoreplication is a trait with an evolutionary significance.

evolutionary biology↗