Complex Interaction Networks Among Cyanolichens of a Tropical Biodiversity Hotspot

Abstract

Interactions within lichen communities include, in addition to close mutualistic associations between the main partners of specific lichen symbioses, also more elusive relationships between members of a wider symbiotic community. Here, we analyze association patterns of cyanolichen symbionts in the tropical montane forests of Taita Hills, southern Kenya, which is part of the Eastern Afromontane biodiversity hotspot. The cyanolichen specimens analyzed represent 74 mycobiont taxa within the order Peltigerales (Ascomycota), associating with 115 different variants of the photobionts genus Nostoc (Cyanobacteria). Our analysis demonstrates wide sharing of photobionts and reveals the presence of several photobiont-mediated lichen guilds. Over half of all mycobionts share photobionts with other fungal species, often from different genera or even families, while some others are strict specialists and exclusively associate with a single photobiont variant. The most extensive symbiont network involves 24 different fungal species from five genera associating with 38 Nostoc photobionts. The Nostoc photobionts belong to two main groups, the Nephroma-type Nostoc and the Collema/Peltigera-type Nostoc, and nearly all mycobionts associate only with variants of one group. Among the mycobionts, species that produce cephalodia and those without symbiotic propagules tend to be most promiscuous in photobiont choice. The extent of photobiont sharing and the structure of interaction networks differ dramatically between the two major photobiont-mediated guilds, being both more prevalent and nested among Nephroma guild fungi and more compartmentalized among Peltigera guild fungi. This presumably reflects differences in the ecological characteristics and/or requirements of the two main groups of photobionts. The same two groups of Nostoc have previously been identified from many lichens in various lichen-rich ecosystems in different parts of the world, indicating that photobiont sharing between fungal species is an integral part of lichen ecology globally. In many cases, symbiotically dispersing lichens can facilitate the dispersal of sexually reproducing species, promoting establishment and adaptation into new and marginal habitats and thus driving evolutionary diversification.

Pesquisa de cianoliquens: uma análise bibliométrica de 1991 a 2022

“…Among the mycobionts, 58% lineages shared its photobiont with at least one other mycobiont, showing the presence of both generalist and specialist lineages. The taxa with apothecia were more generalist with their photobiont than the species lacking apothecia or with vegetative structures reproduction (Kaasalainen et al, 2021), which corroborate with the hypothesis that symbiotic dispersing lichens may facilitates the re-establishment of sexually dispersing species (Belinchón et al, 2015;Kaasalainen et al, 2021;Svensson et al, 2016).…”

Choosing the Right Life Partner: Ecological Drivers of Lichen Symbiosis

“… Kaasalainen et al (2021) demonstrated that cyanolichens share photobionts and revealed the presence of photobiont-mediated lichen guilds. Most of the mycobionts shared photobionts with other non-related fungal species but other photobiont-mycobiont pairs remained isolated.…”

Composition, structure and robustness of Lichen guilds

“…For example, sporeproducing lichens that require a compatible photobiont upon reproduction are indirectly facilitated by the asexual lichens within their guild already established in that environment 28 . Previously, guilds have been defined by photobiont taxonomic identity, but this characterisation has been constrained by the scope of the data sets, which have often included a limited amount of species or geographical locations 16,21,[30][31][32][33][34] . An aggregated network perspective allows us to tackle the structural signature of lichen guilds and provides a solid foundation to address how the general patterns of association in the lichen symbiont network affect its robustness.…”

“…Guild organization has been traditionally linked to photobiont identity (or "photobiont-mediated guild"), and more precisely, at the genus level 27,31,47 . Following this approach, Figure 4a shows the PMAN where species have been labelled according to the genus of their closest photobiont (using a label propagation algorithm, see Methods).…”

“…Much of our current understanding on photobiont-mycobiont partnerships comes from studies involving a few species or geographical areas 16,17,21,22,[31][32][33][34][35][36] . However, mycobiont-photobiont partnerships do not happen in isolation, they are part of a larger web of interactions supporting the assembly and maintenance of communities, and understanding them requires a systemic approach.…”