Disentangling species in the genus Laboulbenia (Fungi, Ascomycota) using molecular phylogenetic data
Background
Fungi of the order Laboulbeniales are among the least studied groups of the Kingdom. They are obligate ectoparasites of arthropod hosts and form microscopic, three-dimensional fruiting bodies—thalli—instead of mycelia. The order, with about 2,325 described species in 145 genera, forms the most diverse fungal lineage associated with representatives of the Phylum Arthropoda, predominantly insects. Research has been long hindered because of their microscopic size, limited morphological traits to distinguish species, the inability of most taxa to grow in axenic culture, and absence of comparative traits to place them among other fungi. The advent of molecular phylogenetic studies has revolutionized our understanding of organismal relationships. These techniques are of particular value when investigating cryptic species of Laboulbeniales (= for which no morphological characters can be used to distinguish them) and may help to precisely estimate species numbers within the group.
Problem
The isolation of DNA from thalli of Laboulbeniales was an early problem to overcome, due to their inability to grow in artificial culture, minute size, and melanized tissue. It may not come as a surprise that only 12 of 174 species of Laboulbeniomycetes described between 2010 and 2020 were accompanied by sequences, mostly of nuclear ribosomal DNA regions, but also mitochondrial small subunit rDNA and the translation elongation factor 1α gene. Molecular phylogenetic data have successfully clarified relationships at lower taxonomic ranks and revealed the existence of cryptic diversity in the Laboulbeniales. Still, generating sequences for Laboulbeniales remains a challenge, especially for material from dried museum collections, specimens collected >10 years ago, or specimens that have melanized thalli—as is the case in many species of Laboulbenia. The genus Laboulbenia includes more than 650 species and many more varieties. Only a handful of these species have been sequenced.
Goal
During this MSc project, the student will collect insects in Belgium and the Netherlands, screen them for the presence of thalli of Laboulbenia, identify the fungi, and generate sequences for them. The goal is to use the generated sequence data to test morphology-based species concepts. Do morphological characters correlate with molecular data? Are cryptic, host-specific species “hidden” within commonly collected taxa that have multiple hosts? The student will generate sequences of multiple loci for Laboulbenia species from different hosts, building on previous work by de Weggheleire (2019) and Haelewaters et al. (2019) to gain an improved understanding of species complexes in the genus. The results of this project are likely to be published in one or more peer-reviewed publications. Practical work will involve fieldwork, screening of insects under stereomicroscope, following DNA extraction protocols, and constructing phylogenetic trees. During the project, the successful student will learn about molecular phylogenetic techniques and fungal taxonomy.
References
De Kesel A. 1998. Identificatie en gastheerspectrum van het genus Laboulbenia in België (Ascomycetes, Laboulbeniales). Sterbeeckia 18: 13-31. [pdf]
De Kesel A, Gerstmans C, Haelewaters D. 2020. Catalogue of the Laboulbeniomycetes of Belgium. Sterbeeckia, 36: 3-143. [pdf]
de Weggheleire S. 2019. Biodiversity of the genus Laboulbenia: are there cryptic species? M.Sc. Thesis, University of Antwerp, Belgium. pp. 1–48. [pdf]
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, De Kesel A, Gorczak M, Bao K, Gort G, Zhao SY, Pfister DH. 2019. Laboulbeniales (Ascomycota) of the Boston Harbor Islands II: species parasitizing Carabidae, and the Laboulbenia flagellata species complex. Northeastern Naturalist 25(Special Issue 9): 110-149. https://doi.org/10.1656/045.025.s906 [pdf]
