Hesperomyces (Fungi, Ascomycota) associated with Hyperaspis ladybirds (Coleoptera, Coccinellidae): Rethinking host specificity

Abstract

Laboulbeniales (Ascomycota, Laboulbeniomycetes) are biotrophic microfungi always attached to the exoskeleton of their arthropod hosts. They do not form hyphae or a mycelium; instead, they undergo determinate growth, developing from a two-celled ascospore to form a multicellular thallus. Hesperomyces virescens has been reported on over 30 species of ladybirds (Coleoptera, Coccinellidae); in reality, it represents a complex of species, presumably segregated by host genus association. In this study, we report on Hesperomyces thalli on Hyperaspis vinciguerrae from the Canary Islands and compare them with the Hesperomyces hyperaspidis described on Hyperaspis sp. from Trinidad. We generated the sequences of the internal transcribed spacer (ITS) region, the large subunit (LSU) nuclear ribosomal RNA gene, and the minichromosome maintenance complex component 7 (MCM7) protein-coding gene. Our phylogenetic reconstruction of Hesperomyces based on a concatenated ITS-LSU-MCM7 dataset revealed Hesperomyces sp. ex Hy. vinciguerrae as a member of the He. virescens species complex distinct from He. virescens sensu stricto (s.s.). It also revealed that the Hesperomyces sp. ex Chilocorus bipustulatus from Algeria is different from He. virescens s.s., which is associated with Chilocorus stigma from the USA. This suggests that the species of Hesperomyces are not solely segregated by host association, but that there is also a biogeographical component involved. Based on these data, we refrained from referring our material from Hy. vinciguerrae to He. hyperaspidis. Finally, we discuss the usefulness of MCM7 as a useful marker for species delimitation in Hesperomyces.

Keywords: Coccinellidae; DNA barcoding; MCM7; arthropod-associated fungi; integrative taxonomy; nuclear ribosomal DNA; phylogeny.

Figure 1

Phylogenetic tree obtained from the maximum likelihood (ML) analysis of a three-locus (ITS–LSU–MCM7) dataset. For every node, the ML bootstrap value (≥70) is given above or next to the branch leading to that node. Species within the Hesperomyces virescens complex are each indicated with their own color. Color scheme from https://colorbrewer2.org by C.A. Brewer, Geography, Pennsylvania State University.

Figure 2

Phylogenetic tree obtained from the maximum likelihood (ML) analysis of a two-locus (ITS–LSU) dataset. For every node, the ML bootstrap value (≥70) is given above or next to the branch leading to that node. Species within the Hesperomyces virescens complex are each indicated with their own color, as in Figure 1 .

Figure 3

Phylogenies of the Hesperomyces virescens species complex, reconstructed from the internal transcribed spacer (ITS) (A), large subunit (LSU) (B), and minichromosome maintenance complex component 7 (MCM7) (C) datasets. For every node, the ML bootstrap value (≥70) is given above or next to the branch leading to that node. Species within the He. virescens complex are each indicated with their own color, as in Figure 1 .

Figure 4

Hesperomyces hyperaspidis Thaxt., slide FH 4989 (holotype). (A) An enlargement of Thaxter’s (1931) original Plate XX: Figure 22. Courtesy of the Archives of the Farlow Herbarium of Cryptogamic Botany, Harvard University. (B) Photo of the same thallus that stood model for Thaxter’s drawing. Scale bar 50 μm.

Figure 5

Hesperomyces sp. ex Hyperaspis vinciguerrae. (A) Mature thallus, slide D. Haelew. 3939a. (B) Mature thallus, slide D. Haelew. 3939a. Cell VI is highly bent. (C) Perithecial tip of a mature thallus, slide D. Haelew. 3939d. Indicated are the two lower lobes (ll), the two upper lobes (UL), and the two perithecial lips (pl), similar to Hesperomyces hyperaspidis. Scale bar 50 μm.