AUTHOR=Pardo-De la Hoz Carlos José , Magain Nicolas , Lutzoni François , Goward Trevor , Restrepo Silvia , Miadlikowska Jolanta 

TITLE=Contrasting Symbiotic Patterns in Two Closely Related Lineages of Trimembered Lichens of the Genus Peltigera

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.02770

DOI=10.3389/fmicb.2018.02770

ISSN=1664-302X

ABSTRACT=<p>Species circumscription is key to the characterization of patterns of specificity in symbiotic systems at a macroevolutionary scale. Here, a worldwide phylogenetic framework was used to assess the biodiversity and symbiotic patterns of association among partners in trimembered lichens from the genus <italic>Peltigera</italic>, section <italic>Chloropeltigera</italic>. We sequenced six loci of the main fungal partner and performed species discovery and validation analyses to establish putative species boundaries. Single locus phylogenies were used to establish the identity of both photobionts, <italic>Nostoc</italic> (cyanobacterium) and <italic>Coccomyxa</italic> (green alga). Distribution and specificity patterns were compared to the closely related clade, section <italic>Peltidea</italic>, which includes mainly <italic>Peltigera</italic> species with trimembered thalli. For section <italic>Chloropeltigera</italic>, eight fungal species (including five newly delimited putative species) were found in association with nine <italic>Nostoc</italic> phylogroups and two <italic>Coccomyxa</italic> species. In contrast, eight fungal species (including three newly delimited putative species) in section <italic>Peltidea</italic> were found in association with only four <italic>Nostoc</italic> phylogroups and the same two <italic>Coccomyxa</italic> species as for section <italic>Chloropeltigera</italic>. This difference in cyanobiont biodiversity between these two sections can potentially be explained by a significantly higher frequency of sexual reproductive structures in species from section <italic>Chloropeltigera</italic> compared to section <italic>Peltidea</italic>. Therefore, horizontal transmission of the cyanobiont might be more prevalent in <italic>Chloropeltigera</italic> species, while vertical transmission might be more common in <italic>Peltidea</italic> species. All <italic>Peltigera</italic> species in section <italic>Chloropeltigera</italic> are generalists in their association with <italic>Nostoc</italic> compared to more specialized <italic>Peltigera</italic> species in section <italic>Peltidea</italic>. Constrained distributions of <italic>Peltigera</italic> species that associate strictly with one species of green algae (<italic>Coccomyxa subellipsoidea</italic>) indicate that the availability of the green alga and the specificity of the interaction might be important factors limiting geographic ranges of trimembered <italic>Peltigera</italic>, in addition to constraints imposed by their interaction with <italic>Nostoc</italic> partners and by climatic factors.</p>