About this Research Topic
Symbiotic systems include two or more different biological species that provide services to each other to maximize the net fitness of all partners. While historically, symbiosis has received less attention than other interactions such as predation or competition, it is increasingly recognized as an important selective force behind evolution. Lichens represent an iconic example of symbiotic life systems. In many cases, lichenized fungi can form symbiotic associations with a range of photobiont species including cyanobacteria. Further, lichenized fungi can also form a kind of association with non-photosynthetic bacteria. The lichen thallus is considered a niche of microbial diversity. These symbionts can have profound effects on lichenized fungal fitness and speciation, and on the community structure and diversity of associated organisms. The fossil record indicates that fungi have been associated with green algae and cyanobacteria for > 400 Myr, thus playing a long and important role in driving the evolution of terrestrial life. The oldest report of a fossil lichens is from the Pre-Cambrian (Paleoproterozoic) of South Africa, dated to 2200 Myr ago. Authors have considered that lichens must have been the first colonizers of land early in Earth history, and hypothesized that lichens originated during the migration of life from sea to land, and referred to them as the “land seaweeds”. However, this has not been supported by molecular data. The view of lichen origins have been debated; some authors hypothesized that first ascomycetes arose from autotrophic “ascophytes”, on soil in moist tropical sites, before the origin of vascular plants and perhaps even before green algae while others argued that heterotrophic fungi evolved first from heterotrophic or parasitic algae in rock pools and lagoons, where they became lichenized through association with cyanobacteria. Recently, molecular phylogenetic studies suggest that the evolution of lichen symbioses occurred several times independently in Ascomycota. Within some lichen-forming fungal lineages, a few authors have suggested that non-lichenized fungi, especially ascomycetes, have evolved from lichenized ancestors, implicitly suggesting that the lichen symbiosis is labile at an evolutionary scale. Lichen symbiosis seems to have played an important role in the evolution of several fungal lineages, both lichenized and non-lichenized but also other associated organisms, e.g. algae and cyanobacteria. However, there are a very few studies available elucidating this using molecular data.
Studies have shown that past climatic changes or geological events could have played a key role in speciation of lichenized fungi. Moreover, patterns and rates of diversification and biogeography have been shown to differ widely amongst different biomes and taxonomic groups.
This Research Topic aims to address the complexity of diversification processes from a pragmatic perspective with an emphasis on molecular phylogenetics and phylogeography but also with contributions from palaeontology and palaeoecology. This global synthesis is necessary to achieve a reliable and accurate basis for more sound generalisations and theoretical proposals, as well as for testing already existing models and hypotheses. The topic has tremendous significance for the understanding of modern biodiversity and its conservation, and environmental drivers affecting diversification. We encourage submissions of original research, reviews, including unsolicited reviews, and mini-reviews on following and/or related topics:
- Studies on any organisation level - intra-specific clades to entire communities- are acceptable.
- Studies of historical biodiversity trends will be considered, provided they have a direct influence on present-day diversity patterns.
- Studies on any kind of environmental driver, ecological process or genetic mechanism linked to the origin and diversity
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