Abstract
The diversity of lichen photobionts is not fully known. We studied here the diversity of the photobionts associated with Cladonia, a sub-cosmopolitan genus ecologically important, whose photobionts belong to the green algae genus Asterochloris. The genetic diversity of Asterochloris was screened by using the ITS rDNA and actin type I regions in 223 specimens and 135 species of Cladonia collected all over the world. These data, added to those available in GenBank, were compiled in a dataset of altogether 545 Asterochloris sequences occurring in 172 species of Cladonia. A high diversity of Asterochloris associated with Cladonia was found. The commonest photobiont lineages associated with this genus are A. glomerata, A. italiana, and A. mediterranea. Analyses of partitioned variation were carried out in order to elucidate the relative influence on the photobiont genetic variation of the following factors: mycobiont identity, geographic distribution, climate, and mycobiont phylogeny. The mycobiont identity and climate were found to be the main drivers for the genetic variation of Asterochloris. The geographical distribution of the different Asterochloris lineages was described. Some lineages showed a clear dominance in one or several climatic regions. In addition, the specificity and the selectivity were studied for 18 species of Cladonia. Potentially specialist and generalist species of Cladonia were identified. A correlation was found between the sexual reproduction frequency of the host and the frequency of certain Asterochloris OTUs. Some Asterochloris lineages co-occur with higher frequency than randomly expected in the Cladonia species.
Highlights
A lichen has been traditionally considered as a stable symbiotic association between a fungus and at least a green alga or a Cyanobacterium [1]
The ITS OTU1 was divided in 3 operational taxonomic units (OTUs) in the actin analyses, and these 3 OTUs correspond with the species A. irregularis, A. glomerata, and A. pseudoirregularis
Recent studies agree in that our knowledge on lichen photobiont diversity is still limited, and much more work using integrative approaches will be necessary in order to characterize that diversity [11, 57]
Summary
The aims of the present study are (1) exploring the biodiversity of the photobionts associated with the genus of lichenforming fungi Cladonia and (2) determining the factors that account for the diversity patterns of the photobionts, as well as for the specificity and selectivity of the mycobionts
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