Abstract:
Determining the causes and consequences of evolutionary and environmental change is central to understanding the diversity of life. Ecological transitions – evolutionary shifts between ecosystems or ecological niches – have played a key role in shaping Earth’s biodiversity. The crustacean order Isopoda provide an excellent study system for ecological transition, with species occupying nearly every environment on Earth. These include terrestrial woodlice, littoral (shoreline) sea-slaters, freshwater pond-lice and diverse marine species, from the giant deep-sea isopod to the notorious ‘tongue-biter’ fish parasite. Crucially, throughout their evolutionary history, isopods have undergone multiple independent transitions (and reversals) among marine, freshwater, terrestrial and host-associated habitats, as well as shifts in feeding ecology. Studying isopod genomes therefore offers a unique opportunity to uncover the genomic basis of ecological adaptation across many different ecosystems. However, until recently, this opportunity has remained out of reach. Like many other crustaceans, generating chromosome-level isopod genomes has proven challenging, with factors such as large genome size, contamination, and sequencing complexities complicating efforts. The Darwin Tree of Life project at the Wellcome Sanger Institute has recently overcome these obstacles, producing the first high-quality chromosomally assembled isopod reference genomes. These mainly include species from isopod suborders Cymothooidea (fish parasites and scavengers) and Asellota (freshwater pond-lice and marine isopods), suggesting there might be a taxonomic bias in sequencing success. Initial analyses reveal dynamic genome evolution across Isopoda – with considerable variation in genome size, chromosome number and repeat content between closely related species, as well as extensive genome rearrangement.