PhD Defence: Guangshuo Li

Thesis title: Taxonomy and adaptations of termite-associated fungi

Supervisor: Professor Michael Poulsen

Assessment committee:

Jonathan Shik (Chair), Department of Biology
Hanna Johannesson, Stockholm University, Sweden
Dimitrios Floudas, Lund University, Sweden

Abstract: Symbiosis is one type of stable interaction between species in same region ranging from mutualism to parasitism, representing unique evolutionary innovation shaping countless complex biological systems. Insects and fungi share a long history of interaction that have resulted in many well-known examples of symbioses, including those between termites and fungi. Termite-fungal symbioses are various, and fungal roles can range from beneficial to harmful. Understanding these symbioses requires identifying the symbionts involved and elaborating their roles and adaptations to be in symbioses. This thesis explores the taxonomy and adaptation in three poorly-understood termite-fungal symbioses. Firstly, we hypothesised that the diversity of Pseudoxylaria, a stowaway fungus in fungus-farming termite colonies, is underestimated in Africa. To test this hypothesis, we constructed a multi-locus phylogeny of Pseudoxylaria from Africa and uncovered eighteen potential novel species. Another group of greatly underexplored symbionts with termites are gut-inhabiting yeast, and in Chapter 2 we identified novel yeast species and strains inhabiting fungus-farming termite guts and revealed their adaptations to utilize xylose, the main building block for hemicellulose. Podaxis has been known for centuries to associate with grass-harvesting termites, but species diversity in the genus and adaptations to symbioses have remained largely unresolved. To improve this, Chapter 3 presents a phylogenomic tree of Podaxis with species descriptions based on a combination of genomics, ecology, morphology, and geographical distribution. This work revealed that basidiospore are significantly different between free-living and termite-symbiotic Podaxis. To delve deeper into this, and genomic consequences of symbioses, we explore in Chapter 4 genome-wide signatures associated with lifestyle and basidiospore sizes. In summary, the work in this thesis enriches our understanding of three termite-fungal symbioses, including the taxonomy of fungal symbionts and allude to fungal adaptations to association with termites.