Topological analysis of orchid-fungal endophyte interaction shows lack of phylogenetic preference

Abstract

Fungal endophytes are known to play a vital role in perpetuation and survival of orchids. While orchid–mycorrhizal relationship has been studied in detail, dynamics of orchid–non-mycorrhizal associations are insufficiently explored. There is paucity of empirical evidence for host specificity, phylogenetic preference, co-evolution, and habitat selection amongst orchids and their non-mycorrhizal endophytes. We explored these aspects by studying the root associated non-mycorrhizal fungal assemblages from 11 epiphytic orchid species in two tropical communities located at Indo-Burma biodiversity hotspot. A total of 94 non-mycorrhizal fungal isolates were mined. Of these 55 isolates could be identified at species level, while 39 isolates were circumscribed at generic level using the ITS region. The core group fungal assemblages predominantly belonged to Ascomycota. The extent of mutualistic reliance was inferred by mapping the bipartite interaction in a phylogenetic framework. The analysis shows that the orchid–non-mycorrhizal associations are neither clade specific nor nested, rather they depend on the availability of suitable fungal taxon at the sites. The study also indicates the absence of phylogenetic preference between the partners. However, topology of the bipartite interaction network suggests that there has been a shift from specialised interaction in the basal clades, to generalised one in the later evolved clades.