https://phaidra.vetmeduni.ac.at/o:4409 Comparative genomics of Ascetosporea gives new insight into the evolutionary basis for animal parasitism in Rhizaria Thoren, Markus Hiltunen Markus Hiltunen Thoren Brännström, Ioana Ioana Brännström Alfjorden, Anders Anders Alfjorden Peckova, Hana Hana Peckova Swords, Fiona Fiona Swords Hooper, Chantelle Chantelle Hooper Holzer, Astrid Astrid Holzer 0000-0002-4916-3172 University of Veterinary Medicine Vienna Bass, David David Bass Burki, Fabien Fabien Burki BMC journal article open access eng Ascetosporea (Endomyxa, Rhizaria) is a group of unicellular parasites infecting aquatic invertebrates. They are increasingly being recognized as widespread and important in marine environments, causing large annual losses in invertebrate aquaculture. Despite their importance, little molecular data of Ascetosporea exist, with only two genome assemblies published to date. Accordingly, the evolutionary origin of these parasites is unclear, including their phylogenetic position and the genomic adaptations that accompanied the transition from a free-living lifestyle to parasitism. Here, we sequenced and assembled three new ascetosporean genomes, as well as the genome of a closely related amphizoic species, to investigate the phylogeny, origin, and genomic adaptations to parasitism in Ascetosporea.Using a phylogenomic approach, we confirm the monophyly of Ascetosporea and show that Paramyxida group with Mikrocytida, with Haplosporida being sister to both groups. We report that the genomes of these parasites are relatively small (12-36 Mb) and gene-sparse (~ 2300-5200 genes), while containing surprisingly high amounts of non-coding sequence (~ 70-90% of the genomes). Performing gene-tree aware ancestral reconstruction of gene families, we demonstrate extensive gene losses at the origin of parasitism in Ascetosporea, primarily of metabolic functions, and little gene gain except on terminal branches. Finally, we highlight some functional gene classes that have undergone expansions during evolution of the group.We present important new genomic information from a lineage of enigmatic but important parasites of invertebrates and illuminate some of the genomic innovations accompanying the evolutionary transition to parasitism in this lineage. Our results and data provide a genetic basis for the development of control measures against these parasites. Genome Reduction Reductive Evolution Evolutionary Transition Phylogeny Protozoa Intracellular Parasite Bonamia Marteilia Paramarteilia Mikrocytos Paramikrocytos http://creativecommons.org/licenses/by/4.0/ https://phaidra.vetmeduni.ac.at/api/object/o:4409/download 10.1186/s12915-024-01898-x https://phaidra.vetmeduni.ac.at/o:605 application/pdf BMC Biology issn:1741-7007 VoR BMC Biology 22 1 4.12 MB 2024