Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2008
Publication Date: 3/7/2008
Citation: Humber, R.A. 2008. Evolution of entomopathogenicity in fungi. Journal of Invertebrate Pathology. 98(3):262-266. Interpretive Summary: This is one of a set of written versions of presentations from the symposium “Are Entomopathogenic Fungi Only Entomopathogens?” at the 2007 meeting of the Society for Invertebrate Pathology. This discussion covers fundamental issues of the origins and nature of the use of living insects or other invertebrates by fungi, and of changes and probable future changes in the nature of the pathogenic relationship between fungi and invertebrate hosts. Because parasitic and pathogenic associations between fungi and insect and other arthropod hosts arose in many basically unrelated lines of fungal evolution, such associations are assumed to have arisen independently and repeatedly. The factors that characterize (and, thereby, help to define) the ability of fungi to obtain nutrients from living invertebrate hosts were discussed from the perspective of a recent general reclassification of all fungi proposed in the wake of a general survey of phylogenetic (evolutionary) relationships among fungi. The types of issues covered here have not been raised in similar terms for many years, and the paper compiles useful literature and concepts whose importance for understanding the biology of fungal pathogens affecting arthropods is often not considered or sufficiently appreciated by insect pathologists.
Technical Abstract: The recent completions of a comprehensive study on the fungal phylogeny and a new classification reflecting that phylogeny form a new basis to examine questions about the origins and evolutionary implications of such major habits among fungi as the use living arthropods or other invertebrates as the main source of nutrients. Because entomopathogenicity appears to have arisen (or, indeed, lost in favor of other sources of nutrition) multiple times in many independent lines of fungal evolution, some of the factors that might either define or enable entomopathogenicity are examined. The constant proximity of populations of potential new hosts seem to have been a factor encouraging the acquisition (or loss) of entomopathogenicity by a very diverse range of fungi, particularly when involving gregarious and immobile host populations of scales, aphids, and cicadas (all in Hemiptera). An underlying theme within the vast complex of pathogenic and parasitic ascomycetes in the Clavicipitaceae (Hypocreales) affecting plants and insects seems to be for interkingdom host-jumping by these fungi from plants to arthropods and then back to the plant or on to fungal hosts. Some genera of Entomophthorales suggest that the associations between fungal pathogens and their insect hosts appear to be trending away from pathogenicity and towards nonlethal parasitism.