Host specificity and diversity of Amylostereum associated with Japanese siricids

Abstract

The mutualism between siricid woodwasps and Amylostereum fungal symbionts has long been considered to be species-specific. Recent studies from North America have challenged this assumption, where native siricids and the introduced Sirex noctilio are clearly swapping symbionts. Whether this pattern is a consequence of invasion or an underappreciated property of siricid biology is unknown. Here we show that the native Japanese siricid, Sirex nitobei, carries both Amylostereum areolatum and Amylostereum chailletii, rather than only A. areolatum as long assumed. Furthermore, all samples from a Urocerus sp. unexpectedly carried, A. chailletii and not Amylostereum laevigatum. Vegetative compatibility group tests revealed extensive clonality, with one VCG present amongst three A. areolatum isolates and six VCGs present amongst 61 A. chailletii isolates. These results contribute to the understanding of insect-fungal fidelity in the siricid-Amylostereum association and, together with other studies, suggest that host tree influences Amylostereum species occurrence, perhaps more strongly than wasps.

Evolutionary priming and transition to the ectomycorrhizal habit in an iconic lineage of mushroom-forming fungi: is preadaptation a requirement?

“…Here, we describe trends in genomic architecture and gene content in twenty representative species of Russulales. Our dataset contains fourteen previously unanalyzed genomes, including 11 species of ECM Russulaceae and their saprotrophic sister group ( Gloeopeniophorella convolvens ), and Amylostereum chailletii , a white-rot wood-decomposer that is associated with siricid woodwasps in a timber pathogenic symbiosis (Fitza et al 2016). Our analysis elucidates patterns of functional diversity that have evolved within the ECM symbiotrophs, including evolution of PCWDEs, retention of genes to scavenge nitrogen compounds in soil organic matter, secondary metabolism, and TE invasion favoring duplication of species-specific genes.…”

Symbionts mediate oviposition behaviour in invasive and native woodwasps

“…Preference for this fungal strain by S. nigricornis in the present study is consistent with the fact that larvae of this native Sirex are known to develop in the same trees as S. noctilio (Long et al ., ; Ryan et al ., ; Hajek et al ., ) and horizontal transmission of Amylostereum between Sirex species appears to occur within trees (Hajek et al ., ; Wooding et al ., ). Sirex species were previously considered specific to single Amylostereum species (Talbot, ; Gilbertson, ), although studies of Sirex and Urocerus have demonstrated flexibility in the Amylostereum species being carried (Wooding et al ., ; Fitza et al ., ; Hajek et al ., ), in particular by two Sirex native to North America, including S. nigricornis (Hajek et al ., ; Olatinwo et al ., ). Although relatively little is understood about the biology and behaviour of S. nigricornis , flexibility in symbiont use could be advantageous now that the competitive S. noctilio is present.…”

Pest categorisation of Sirex nitobei

“…The fungus vectored by S. nitobei is either Amylostereum areolatum (Chaillet ex Fries) Boidin (in most cases) or A. chailletii (Pers.) Boidin (Kobayashi et al., 1978 ; Fitza et al., 2016 ; Wang et al., 2021 ). There are no records of both fungi being found together in any individual wasp.…”

“…No intraspecific diversity is reported for S. nitobei . However, the symbiotic fungus species has been observed to vary between individuals, with associations with either Amylostereum areolatum or A. chailletii (Fitza et al., 2016 ). Intraspecific variation within A. areolatum has also been observed.…”