Doctoral defence: Iryna Yatsiuk "Evolution, species delimitation and diversity in myxomycetes: Arcyria and allied genera"

On October 21 at 10:15 Iryna Yatsiuk will defend her doctoral thesis "Evolution, species delimitation and diversity in myxomycetes: Arcyria and allied genera" for obtaining the degree of Doctor of Philosophy (in Botany and Mycology).

Supervisors:
Professor Urmas Kõljalg, University of Tartu
Professor Leontyev Dmytro, Kharkiv National Pedagodical University, Ukraine

Opponent:
Associate Professor Ivan García-Cunchillos, University of Warsaw, Poola

Summary:
Myxomycetes (slime molds) play vital roles in ecosystems, yet remain largely unnoticed. Neither plants, animals, nor fungi, myxomycetes are unique organisms with a complex life cycle. They start as amoebas living in soil, dead wood, and litter, where they feed on bacteria and other microorganisms, and are themselves the food for small animals. Then, amoebas aggregate into visible slimy structures – plasmodia, and eventually transform into spore-bearing fruiting bodies.

Despite their ecological functions, myxomycetes are often overlooked in taxonomical research. This work aimed to fill gaps in understanding their evolution, species boundaries, and biodiversity, mostly focusing on the genus Arcyria, family Arcyriaceae. We morphologically and genetically studied 33 species of Arcyria collected worldwide. Arcyria was confirmed to be polyphyletic, comprising two distant clades. Most of the traits, previously used to delimit taxa in Arcyriaceae appeared to be homoplastic or symplesiomorphic. However, the color of the spores was more consistent with the phylogeny and helped us delimit the genera and families. As a result, the family Arcyriaceae was emended, a new family Hemitrichiaceae established, a new genus Spiromyxa described, and the genus Heterotrichia resurrected. Most of examined Arcyria species turned out to be species complexes; para- or polyphyletic groups.

We also explored application of DNA barcoding to delimit myxomycete species. Generally, a local barcoding gap between species was present. However, there were exceptions such as cryptic species that look alike but are genetically different, and those that look different but have similar DNA. Even at the genus level there was no single similarity threshold that would perfectly sort out sequences into species.

Another part of this thesis summarizes our effort in collecting and publishing primary data on myxomycete diversity following FAIR (Findable, Accessible, Interoperable, Reusable) principles.