Screening insect collections for the presence of ectoparasitic microfungi

Background

There is an increasing understanding that understudied groups of organisms should receive more attention due to large-scale conservation efforts. Ecosystem conservation needs an all-encompassing approach, thus incorporating those taxa that are poorly known—how can we protect biodiversity if we do not what is present? Two of these understudied groups are parasites and microfungi. Laboulbeniales is an order of parasitic microfungi (!) within the class Laboulbeniomycetes. The order includes some of the least studied representatives in the Kingdom Fungi. These fungi generally do not kill their hosts; however, the host fitness can be reduced if the parasite density is high. Hosts of Laboulbeniales are members of three subphyla of Arthropoda: Chelicerata (mites, harvestmen), Myriapoda (millipedes), and Hexopoda (insects). Approximately 80% of all described Laboulbeniales infections occur on Coleoptera (beetles), followed by Diptera (flies), Hemiptera (true bugs), and Dermaptera (earwigs) as the most frequently reported host groups. Most Laboulbeniales exhibit a high level of host specificity. Some taxa that were previously thought to have many different hosts have turned out to be complexes of multiple species, segregated in part by host.

Problems

Laboulbeniales are difficult to study due to a combination of factors: they are microscopic in size, molecular research is in its infancy, hampering understanding of evolutionary relations and species delimitation, the classification is hopelessly dated, and the group is studied by only a few specialists spread around the world. One of the major problems encountered with Laboulbeniales is similar to that of Fungi in general: the vast majority of the estimated diversity is unknown. The estimated diversity for the entire kingdom of Fungi is between 1.5 and 6 million species, whereas thus far only 148,000 species have been described. In other words, as much as 90.1 to 97.5% of the expected diversity of fungi is to be discovered and formally described. The same is true for Laboulbeniales. A total of 2,325 species have been described but an extrapolation from fieldwork in Sulawesi estimated between 15,000 and 75,000 species. Again, this means that 84.5 to 96.9% of the expected diversity of Laboulbeniales is yet to be described. It is expected that the majority of the earth’s diversity has already been collected but is still awaiting study in natural history collections. For Laboulbeniales this material consists of dried and pinned insect collections. Laboulbeniales on their hosts remain intact and so insects can be easily studied under a stereoscope for the presence of these microfungi. In this way, tens of undescribed of Laboulbeniales have been discovered.

Goals

The student who will take on this project will screen the Taxon Expeditions ground beetle (Carabidae) collection for the presence of Laboulbeniales. This collection is readily accessible and well-curated. Infected specimens will be separated and Laboulbeniales microfungi will be studied based on morphology and, when possible, molecular methods. Morphology will include the preparation of permanent slide mounts and identification based on light microscopy observation of morphological characteristics. Molecular methods will involve DNA extraction using protocols optimized for microfungi. Laboulbeniales fungi have complex cell wall structures that often remain difficult to break open to obtain a sufficient amount of DNA. Another factor that may affect the success of molecular work is how hosts were killed and conserved. The Taxon Expeditions collection is well documented in terms of killing and preservation method (e.g., acetic acid, ethyl acetate vapor, 70% ethanol, 100% ethanol, ethylene glycol). Besides, while older material is generally unavailable for molecular work, most of the Taxon Expeditions collection is relatively young (sampled in the past two years). Upon the discovery of new species, these will be formally described following best practices. In addition, the specimen data of all previously unstudied specimens will be digitized in the Taxon Expeditions collection database.

The student will gain knowledge in curation of natural history collections, parasite biology, Laboulbeniales ecology, molecular protocols, and integrative taxonomy approaches. This project will be in collaboration with Dr. Menno Schilthuizen from Taxon Expeditions and Naturalis Biodiversity Center.

References

Aime MC, Miller AN, Aoki T, Bensch K, Cai L, Crous PW, Hawksworth DL, Hyde KD, Kirk PM, Lücking R, May TW, Malosso E, Redhead SA, Rossman AY, Stadler M, Thines M, Yurkov AM, Zhang N, Schoch CL. 2021. How to publish a new fungal species, or name, version 3.0. IMA Fungus 12: 11. https://doi.org/10.1186/s43008-021-00063-1

Haelewaters D, Blackwell M, Pfister DH. 2021. Laboulbeniomycetes: Intimate fungal associates of arthropods. Annual Review of Entomology 66: 257-276. https://doi.org/10.1146/annurev-ento-013020-013553 [pdf]

Haelewaters D, De Kesel A. 2020. Checklist of thallus-forming Laboulbeniomycetes from Belgium and the Netherlands, including Hesperomyces halyziae and Laboulbenia quarantenae spp. nov. MycoKeys 71: 23-86. https://doi.org/10.3897/mycokeys.71.53421 [pdf]

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]

Haelewaters D, Rossi W. 2017. Laboulbeniales parasitic on American small carrion beetles: new species of Corethromyces, Diphymyces, and Rodaucea. Mycologia 109(4): 655-666. https://doi.org/10.1080/00275514.2017.1379118 [pdf]

Halme P, Heilmann-Clausen J, Rämä T, Kosonen T, Kunttu P. 2012. Monitoring fungal biodiversity – towards an integrated approach. Fungal Ecology 5(6): 750–758. https://doi.org/10.1016/j.funeco.2012.05.005 [pdf]