Hesperomyces halyziae Haelew. & De Kesel, 2020

Haelewaters, Danny & Kesel, Andre De, 2020, Checklist of thallus-forming Laboulbeniomycetes from Belgium and the Netherlands, including Hesperomyces halyziae and Laboulbenia quarantenae spp. nov., MycoKeys 71, pp. 23-86 : 23

Hesperomyces halyziae Haelew. & De Kesel sp. nov. Figure 3

Etymology.

Referring to the host genus, Halyzia .

Diagnosis.

Morphologically very similar to other taxa within H. virescens sensu lato, but forming a distinct species supported by ITS data. The ITS sequence shares 95.8-97.9% identity with H. virescens s.l. from Harmonia axyridis , and 96.5-95.4% with H. virescens s.l. from Adalia bipunctata / A. decempunctata . Unique molecular synapomorphies in the ITS at positions 478, 517, 652.

Types.

Holotype: The Netherlands, Noord Brabant Province, Tilburg, nature reserve De Kaaistoep, 51.5333333N, 5.0166667E, 11 Aug. 2015, leg. H. Spijkers & P. van Wielink, on female Halyzia sedecimguttata (Linnaeus, 1758) ( Coleoptera , Coccinellidae ) (NNKN), slide D. Haelew. 955a (FH, 4 juvenile and 3 mature thalli, left elytron), reported as Hesperomyces virescens in Haelewaters and van Wielink (2016). Paratypes: Belgium, Province Vlaams-Brabant, Meise, Domein van Bouchout, 50.927925N, 4.333069E, 28 Mar. 2019, leg. C. Gerstmans, on H. sedecimguttata (BR, CG437-CG440), slides BR5020212155379V, BR5020212156406V, BR5020212157434V, and BR5020212158462V; reported as Hesperomyces virescens sensu lato in De Kesel et al. (2020). Ibid., 1 Apr. 2019, leg. C. Gerstmans, on H. sedecimguttata (BR, CG441-442), slides BR5020212159490V and BR5020212160236V; reported as Hesperomyces virescens sensu lato in De Kesel et al. (2020).

Description.

Thallus 335-453 μm long from foot to perithecial apex; colored yellow except for a somewhat darker region right above the foot. Cell I obtriangular, 2.0-2.5 × longer than broad, broadening distally, with very oblique septum I-II. Cell II longer than broad, 23-28 × 16-21 µm, subtrapezoidal in section. Cell III always smaller than cell II, 14-20 × 14-19 µm, with inflated dorsal cell wall. Primary appendage consisting of 4 superposed cells, 61-67 μm long; in the same axis as cells I and III, separated from the latter by the constricted primary septum; its basal cell somewhat longer than broad, longer than each of the remaining cells of the appendage; second to fourth cells carrying a single antherium externally, the fourth cell also carrying a second upwardly directed antherium. Antheridia flask-shaped, with slightly (dorsally and/or basally) curved efferent necks, the upper antheridium carrying at its dorsal side a pointed process, which represents the original ascospore apex. Cell VI with subparallel margins to broadening distally, 33-70 × 23-33 μm. Perithecium 194-291 × 62-86 μm (not including basal cells), symmetric or with the anterior margin convex and the posterior one almost straight or concave; broadest near the upper third, then gradually tapering towards the apex; apex complex with 2 short lower lobes, 2 upper (terminal) lobes, and 2 prominent lips surrounding the ostiole; lower lobes tapering to a rounded tip, the ventral lobe outwardly directed; terminal lobes unicellular, elongated, 29-42 μm in length, curved upwards and outwardly; ostiole with two lips, 25-29 μm in length, one lip triangular, the other slightly shorter, blunt or rounded, basally carrying the remainder of the trichogyne. Ascospores 70-85 μm long, with conspicuous slime sheath only surrounding the larger cell .

Material sequenced.

The Netherlands, Noord Brabant Province, Tilburg, nature reserve De Kaaistoep, 51.5333333N, 5.0166667E, 11 Aug. 2015, leg. H. Spijkers & P. van Wielink, on female Halyzia sedecimguttata ( Coleoptera , Coccinellidae ) (NNKN), isolate D. Haelew. 955b (7 thalli, elytra, ITS: MG757813).

Hosts and distribution.

On Halyzia sedecimguttata from Belgium and the Netherlands. Previously reported as H. virescens ( Haelewaters and van Wielink 2016, Haelewaters et al. 2017) and H. virescens sensu lato ( De Kesel et al. 2020). One unverified record is available from France ( Justamond 2019).

Notes.

Supported by multi-locus phylogenetic analyses and sequence-based species delimitation methods, Haelewaters et al. (2018) showed that H. virescens Thaxt. is a complex of multiple species, segregated by host. The authors proposed to "restrict H. virescens sensu stricto to those thalli found on Chilocorus stigma , the host species on which the fungus was originally described" ( Thaxter 1891). Here, we included two isolates from C. stigma (Say, 1835), and found the clade representative of H. virescens sensu stricto. Based on this analysis and previous work ( Haelewaters et al. 2018), we can start describing the individual clades as distinct species. A monographic work with formal descriptions for the seven other species within H. virescens s.l. is in preparation, but in the light of this checklist we decided to describe H. halyziae , which was only known from a single collection in the Netherlands until we recently collected it in Belgium (Mar.-Apr. 2019).

Haelewaters and van Wielink (2016) reported an infected specimen of Halyzia sedecimguttata from nature reserve De Kaaistoep in the Netherlands. In 1997-2015, 476 individuals of H. sedecimguttata were collected on a lighted white sheet and screened for presence of Laboulbeniales , only resulting in one individual (parasite prevalence 0.2%). In Belgium, a population of infected H. sedecimguttata was found at the Meise Botanic Garden. Specimens were collected in spring 2019 while they were leaving their overwintering place-deep cracks in the woodwork of a small forest chapel. Screening of 46 specimens of H. sedecimguttata revealed nine infected ones (parasite prevalence 19.5%). This ladybird species seems to overwinter singly or in small congregations in narrow overwintering places, including in leaf litter, under foliage on stone walls, on trunks and branches ( Majerus and Williams 1989). This congregation behavior is beneficial for transmission of the fungus and is also observed in Harmonia axyridis ( Haelewaters et al. 2017).

Morphologically, H. halyziae is very similar to what we have thus far accepted as H. virescens . Within the Kingdom Fungi, there is an incredible diversity that cannot be perceived through morphology. Cryptic species are being uncovered in Agaricomycetes (e.g., Stefani et al. 2014; Sánchez-García et al. 2016), Lecanoromycetes (e.g., Singh et al. 2015), Leotiomyces (e.g., Grünig et al. 2008), Pucciniomycetes ( Bennett et al. 2011), Ustilaginomycetes (e.g., Li et al. 2017), and other major clades. And while the Laboulbeniales has been the subject of a large-scale study to estimate the global species richness of the group ( Weir and Hammond 1997), cryptic diversity was not part of the equation. In other words, the number of estimated species of Laboulbeniales , between 15,000 and 75,000, is likely to be corrected to include cryptic species. We note that the recognition of H. halyziae is only possible through molecular data and host association. Our current understanding is that, within this species complex, there is a strict parasite-host association, with one parasite found only on one host. We think that this host specificity exists at the genus level, given the Adalia clade (Figure 1 ), which includes isolates from thalli removed from two host species within the same genus.

Figures

Figure 1. Maximum clade creditability tree of Hesperomyces isolates reconstructed from an ITS dataset, with H. coleomegillae as outgroup. The topology is the result of Bayesian inference performed with BEAST. For each node, ML BS (≥ 65) and Bayesian pp (≥ 0.7) are presented above / below the branch leading to that node. Hesperomyces virescens sensu lato is highlighted with light gray shading, isolates are color-coded by host; H. virescens sensu stricto and H. halyziae sp. nov. are highlighted with dark gray shading.

Figure 3. Hesperomyces halyziae Haelew. & De Kesel from Halyzia sedecimguttata A mature thallus from slide D. Haelew. 955 a, holotype B mature thallus from slide BR 5020212156406 V. Scale bar: 100 µm.