Kaishian P, Lubbers M, Ben Fekih I, de Groot MD, Schilthuizen M, Haelewaters D. 2026. Definitions of parasites and pathogens through time. In: Haelewaters D (ed.) Biodiversity and Evolution of Fungal Parasites and Pathogens. Academic Press, Cambridge, Massachusetts. https://doi.org/10.22541/au.165712662.22738369/v2 [preprint]
Scientists ought to apply universally accepted definitions to technical terms to enable precise communication and discussion. Throughout history, many definitions have shifted, such as those of important terms in evolutionary biology, modes of life, and the nature of interactions. Conversely, throughout history, important terms have been used without proper definition. Two such terms are parasites and pathogens. An extensive body of literature considers parasites and pathogens to be categorically negative, which has resulted in definitions that lack objectivity and limit a full understanding of the biology of these organisms. Different interpretations have resulted in shifting definitions, in turn causing confusion. Here, we present the remarkable history of both definitions, an overview of alternative definitions put forward throughout history, and a working definition for both terms. We find that the line between what is a parasite or a pathogen is often blurry, and is additionally complicated due to the multi-modal nature of interactions.
Keywords: Complex Interactions; Definition; Parasites; Pathogens
Luo C, Haelewaters D, Krings M. 2026. Fossils of parasitic fungi. In: Haelewaters D (ed.) Biodiversity and Evolution of Fungal Parasites and Pathogens. Academic Press, Cambridge, Massachusetts. https://doi.org/10.22541/au.166696714.49994889/v2 [preprint]
Parasitic fungi occur in virtually every ecosystem, where they can significantly affect the functions of other organisms. Fungal parasites were probably also widespread in the geologic past. However, evidence of fossil fungi and their ecological roles is relatively rare. Here we demonstrate a spectrum of (putative) parasitic relationships in ancient continental ecosystems, using fossil examples of Chytridiomycota, zygomycetous fungi, Basidiomycota, and Ascomycota, along with several fungal fossils whose affinities remain unknown, from different periods of the Phanerozoic. Although many of the hosts no longer exist, the fungi involved mostly appear morphologically very similar to extant forms.
Keywords: Amber; Chert; Coal Ball; Host Response; Interaction; Preservation
Bermúdez-Cova MA, Haelewaters D, de Bekker C, Piepenbring M, Schoutteten N, Quandt CA. 2026. Hyperparasitic fungi—definitions, diversity, ecology, and research. In: Haelewaters D (ed.) Biodiversity and Evolution of Fungal Parasites and Pathogens. Academic Press, Cambridge, Massachusetts. https://doi.org/10.22541/au.168787020.07281183/v2 [preprint]
Even parasites have parasites. By definition, a hyperparasite is an organism capable of parasitizing another parasite. Hyperparasitism caused by fungi is a common phenomenon in nature, but it has been poorly studied. This life history strategy evolved several times in the fungal tree of life, and is crucial in the maintenance of ecosystems as well as in the mediation of parasite–host interactions. Although the interest for hyperparasitic fungi is growing in the context of biological control, hyperparasitism is not ecologically and evolutionarily understood. This chapter summarizes the most relevant aspects of the terminology, diversity, and ecology of hyperparasitic fungi on both fungal and non-fungal hosts. We also discuss the problems related to molecular research on hyperparasitic fungi. As they represent a hidden source of diversity, it is necessary to increase sampling efforts and to undertake further morphological, molecular, and ecological studies to understand these fungi and their potential biotechnological and pharmaceutical uses.
Keywords: Ampelomyces quiqualis; Biological Control; Host; Hyperparasite; Trichoderma; Trophic Interactions
Haelewaters D, Gorczak M, Kaishian P, De Kesel A, Blackwell M. 2021. Laboulbeniomycetes, Enigmatic Fungi With a Turbulent Taxonomic History. pp. 263-283. In: Zaragoza Ó, Casadevall A (eds.) Encyclopedia of Mycology, Volume 1. Elsevier, Oxford. https://doi.org/10.1016/B978-0-12-819990-9.00049-4 [pdf]
Phylogenetic studies of Laboulbeniomycetes support recognition of three orders (Herpomycetales, Laboulbeniales, Pyxidiophorales) and two unnamed clades containing conidial, arthropod-associated fungi and a poorly known perithecial genus,
Subbaromyces. Herpomycetales and Laboulbeniales include obligate arthropod-associated biotrophs characterized by a parenchymatous thallus of several thousand cells. Pyxidiophorales are hyphal mycoparasites with an unusual three-morph life cycle. The two-celled ascospore with a distinctive apparatus for attachment to arthropods ties together all Laboulbeniomycetes. The complex morphologies and life histories of these fungi are described as a background for research directions that will rely heavily on molecular methods, including phylogenomics, with emphasis on host–parasite relations.
Keywords: Arthropod dispersal; Ascomycota; Biotrophic; Chantransiopsis; Coreomycetopsis; Herpomycetales; Laboulbeniales; Laboulbeniopsis; Perithecial Fungi; Pyxidiophorales; Subbaromyces; Systematics; Tetromeronycha; Thaxteriola
Quandt CA, Haelewaters D. 2021. Phylogenetic Advances in Leotiomycetes, an Understudied Clade of Taxonomically and Ecologically Diverse Fungi. pp. 284-294. In: Zaragoza Ó, Casadevall A (eds.) Encyclopedia of Mycology, Volume 1. Elsevier, Oxford. https://doi.org/10.1016/B978-0-12-819990-9.00052-4 [pdf]
The class Leotiomycetes encompasses many fungi that were historically classified as inoperculate discomycetes. Molecular phylogenetics has changed our perception of the diversity of higher taxonomic lineages and morphologies in the class as well as our understanding of how these clades are related to one another. Leotiomycetes are found in all environments where researchers have explored and have myriad ecological strategies – including economically important pathogens (e.g., powdery mildews on various plants and the causal agent of the white-nose syndrome of bats), endophytes, saprobes, and mycorrhizae. In this article, we provide a summary of the morphological and ecological diversity of Leotiomycetes, and an overview of the taxonomic diversity and systematics. Major challenges in studying this group include historical biases in sampling outside of temperate Europe and North America and a lack of sequence data for many taxa especially in the sprawling mega-order Helotiales. With the help of environmental sequencing and genomic-scale data, researchers are beginning to reveal new perspectives on Leotiomycetes ecology, evolution, and systematics.
Keywords: Ascomycota; Discomycetes; Erysiphaceae; Helotiales; Leotiales; Phacidiales; Rhytismatales; Sampling Bias; Systematics; Thelebolales
Haelewaters D, Dick CW, Cocherán Pittí KP, Dittmar K, Patterson BD. 2021. Chapter 21. Bats, Bat Flies, and Fungi: Exploring Uncharted Waters. pp. 349-371. In: Lim BK, Fenton MB, Brigham RM, Mistry S, Kurta A, Gillam EH, Russell A, Ortega J (eds.) 50 Years of Bat Research. Fascinating Life Sciences. Springer, Cham. https://doi.org/10.1007/978-3-030-54727-1_21 [pdf]
Bats serve as hosts to many lineages of arthropods, of which the blood-sucking bat flies (Nycteribiidae and Streblidae) are the most conspicuous. Bat flies can in turn be parasitized by Laboulbeniales fungi, which are biotrophs of arthropods. This is a second level of parasitism, hyperparasitism, a severely understudied phenomenon. Four genera of Laboulbeniales are known to occur on bat flies,
Arthrorhynchus on Nycteribiidae in the Eastern Hemisphere,
Dimeromyces on Old World Streblidae,
Gloeandromyces on New World Streblidae, and
Nycteromyces on Streblidae in both hemispheres. In this chapter, we introduce the different partners of the tripartite interaction and discuss their species diversity, ecology, and patterns of specificity. We cover parasite prevalence of Laboulbeniales fungi on bat flies, climatic effects on parasitism of bat flies, and coevolutionary patterns. One of the most important questions in this tripartite system is whether habitat has an influence on parasitism of bat flies by Laboulbeniales fungi. We hypothesize that habitat disturbance causes parasite prevalence to increase, in line with the “dilution effect.” This can only be resolved based on large, non-biased datasets. To obtain these, we stress the importance of multitrophic field expeditions and international collaborations.
Keywords: Ectoparasitic Fungi; Fieldwork; Hippoboscoidea; Hyperparasites; Multitrophic Interactions; Parasitism
