Ophiocordyceps salganeicola, a parasite of social cockroaches in Japan and insights into the evolution of other closely-related Blattodea-associated lineages

Abstract

The entomopathogenic genus Ophiocordyceps includes a highly diverse group of fungal species, predominantly parasitizing insects in the orders Coleoptera, Hemiptera, Hymenoptera and Lepidoptera. However, other insect orders are also parasitized by these fungi, for example the Blattodea (termites and cockroaches). Despite their ubiquity in nearly all environments insects occur, blattodeans are rarely found infected by filamentous fungi and thus, their ecology and evolutionary history remain obscure. In this study, we propose a new species of Ophiocordyceps infecting the social cockroaches Salganea esakii and S. taiwanensis, based on 16 years of collections and field observations in Japan, especially in the Ryukyu Archipelago. We found a high degree of genetic similarity between specimens from different islands, infecting these two Salganea species and that this relationship is ancient, likely not originating from a recent host jump. Furthermore, we found that Ophiocordyceps lineages infecting cockroaches evolved around the same time, at least twice, one from beetles and the other from termites. We have also investigated the evolutionary relationships between Ophiocordyceps and termites and present the phylogenetic placement of O. cf. blattae. Our analyses also show that O. sinensis could have originated from an ancestor infecting termite, instead of beetle larvae as previously proposed.

Keywords: Ascomycota; Cockroaches; Entomopathogenic fungi; Host-jumps; Hypocreales; Ophiocordyceps sinensis; Termites.

Fig. 1

Ophiocordyceps blattae and O. cf. blattae. a the original illustration of O. blattae showing the ascoma emerging laterally from the host thorax (Petch 1924). b and c (K98612 – holotype deposited in the Kew Gardens Fungarium). d and e Additional specimen collected by Petch in 1914, same location as the holotype K(M)264510. f O. cf. blattae from Thailand used in this study with two ascomata arising laterally on both sides (deposited at Biotech Fungal Collections as MY34765) (del. M. G. Moriguchi). a–e; images by Lee Davis, Royal Botanic Garden, Kew

Fig. 2

Ophiocordyceps salganeicola emerging from Salganea esakii in its natural habitat in Yakushima island, Kagoshima. a and b Visible part of the ascoma, emerging from a hole in the wood. c and d Hosts buried in the wood, visible only after digging a few centimeters. e Infected host in its very rare nymphal stage

Fig. 3

Southwestern part of Japan showing collection sites of O. salganeicola specimens used in this study. Specimen details are indicated in Table 1. The map was retrieved and edited from Geospatial Information Authority of Japan

Fig. 4

Ophiocordyceps salganeicola at various stages of development (del. M. G. Moriguchi). a Sexual morph of O. salganeicola growing on Salganea esakii collected in Miyazaki, 22 Jun. 2005. b Sexual morph on S. esakii collected in Yakushima, 17 Jun. 2017. with a close-up illustration of perithecia. c Early-stage specimen. d Mid-stage specimen (Mori04; see Tables 1 and 2) collected in Katsuu-dake, Nago-shi, Okinawa, 23 Apr. 2016. e Mature specimen from Kunigami-son, Okinawa, collected 29 May 2016

Fig. 5

Maximum likelihood tree of Ophiocordycipitaceae obtained from RAxML analyses based on a concatenated set of 5 genes (SSU, LSU, TEF, RPB1 and RPB2). Colored branches reflect Ancestral Character State Reconstruction (ACSR) analyses based on host associations (See legend at the bottom-left) and pie-charts represent the probability for the association with host orders. Dashed lines indicate ambiguous association. Host pictures by Alex Wild and Shizuma Yanagisawa

Fig. 6

Ophiocordyceps salganeicola on Salganea taiwanensis (dried specimen) from Kunigami-son, Okinawa (TNS-F-60532). a Two ascomata arising from S. taiwanensis. b Close-up of dried ascoma. c Cross section of ascoma showing the perithecial arrangement. d Ascus with spirally twisted ascospores. e Perithecial ostiole. f and g 8-celled ascospore. Scale bars = c 200 μm, d 15 μm, e 10 μm, f and g 20 μm. Presented as JPMA124 in

Fig. 7

Ophiocordyceps salganeicola on Salganea esakii (fresh specimen) from Yakushima, Kagoshima (TNS-F-91239). a Salganea esakii with a single robust ascoma; b Close-up showing early stage ascoma arising from ventral pronotum; c and d Close-up of ascoma; e Cross-section of ascoma; f and g Perithecia; h Ascospores within ascus; i and j 8-celled ascospores. Presented as JPMA106 in Fig. 5

Fig. 8

Ophiocordyceps salganeicola anamorph and germinated ascospores. a and b Hirsutella-like conidiogenous cells, c and d Ascospores germination after 72 h