Ophiostomatoid fungi associated with fungus farming insects in South Africa

Abstract

Symbiosis is the term used to describe the different forms of communal life that can exist between two unlike organisms. Primarily this involves interaction in one of three forms: mutualism where both partners benefit from their association; antagonism where one or both partners are harmed by their association; and commensalism where one partner derives benefit but the other is neither harmed nor profited from their association. Many different forms of symbioses have been described between insects and microbes and these include short, simple interactions as well as obligate associations. Aside from humans, sophisticated agricultural farming practices have only been found for three insect groups, colloquially known as fungus-farmers. These three groups – the attine ants, the macrotermitinae termites, and the ambrosia beetles - each independently evolved an obligate mutualism with fungal partners that they actively cultivate and maintain within their nests and utilize as a primary source of nutrition. The primary focus of this PhD thesis was that of the association that exists between bark and ambrosia beetles and their respective fungal partners and the genomic signatures of these associations. Additionally, the unexpected and interesting discovery of Ophiostomatoid fungi from fungus-growing macrotermitinae termites was also investigated. Very little research on ambrosia beetles and their fungal partners has been conducted in South Africa. However, the accidental introduction of the devastating Polyphagous Shot Hole Borer into the country has sparked renewed interest into this topic. The primary focus of the research included in this thesis has consequently been on ambrosia beetles in South Africa. This is also the topic of the literature review (Chapter 1) at the start of the thesis. However, given the many commonalities regarding their associations with fungi, we have also included a study that led to the discovery of Ophiostomatoid fungi associated with fungus-farming termites. The background literature relating to this association is provided in the introduction to that study and it is also a topic that has been thoroughly treated in a number of recent reviews. In Chapters 2-4 I explore the diversity of Ophiostomatoid fungi associated with fungusfarming insects in South Africa. In Chapter 2, I report four species of Ophiostomatalean species associated with commonly found ambrosia beetles in the country. One of these species is reported from South Africa for the first time and two are described as novel species. In Chapter 3, I report for the first time the presence of the granulate ambrosia beetle and its Microascalean associate, Ambrosiella roeperi, in South Africa and highlight the potential threat that this beetle and its fungal symbiont poses to South Africa’s agricultural industry. In Chapter 4, I investigate three species of Ophiostomatalean fungi discovered on the abandoned Termitomyces fungus combs of fungus-farming termites. Using both culture- based and genomics techniques, I describe these newly discovered Ophiostomatalean fungi and investigate their distinct lifestyle. In Chapter 5, I delve more deeply into the relationship shared between Sordariomycete fungi known to be associated with arthropods. In this chapter, I attempt to elucidate how the relationship with their arthropod partners has influenced their genomic evolution. Using whole genome sequences and comparative genomics methods I investigate the traits shared amongst the Ascomycete ambrosia fungi, as well as investigate how these fungi differ genetically from their close relatives. Finally, as a supplementary chapter to this thesis, I provide a comprehensive record of bark and ambrosia beetle species present in South Africa. This is justified by the fact that other studies included in this thesis involved extensive trapping of bark and ambrosia beetles, many of which had not previously been recorded in the country. This record increases the currently recorded number of these insects from South Africa from 163 to 260. Additionally, 22 species are reported from the county for the first time. It was decided to place this chapter as supplementary material and not within the main body of the thesis because it did directly capture the common theme of Ophiostomatoid fungi associated with fungus-farming insects.