Molecular phylogeny and symbiotic selectivity of the green algal genus Dictyochloropsis s.l. (Trebouxiophyceae): a polyphyletic and widespread group forming photobiont-mediated guilds in the lichen family Lobariaceae.

Dictyochloropsis s.l. is an ecologically important, common but little-studied genus of green algae. Here, we examined the diversity and host selectivity of algae attributed to this genus at both species-to-species and species-to-community levels. We conducted a molecular investigation of 15 cultured strains and several lichen photobionts, using 18S rRNA, rbcL and ITS sequence data. We further used seven alga-specific microsatellite markers to study algal sharing among fungi of the family Lobariaceae in two populations in Madeira and Taiwan (454 lichens). We found that the genus Dictyochloropsis s.l. is polyphyletic. Dictyochloropsis clade 1 comprises only free-living algae whereas Dictyochloropsis clade 2 includes lichenized algae as well as free-living algae. Fungal selectivity towards algae belonging to Dictyochloropsis clade 2 is high. Selectivity varies geographically, with photobionts being restricted to a single region. Finally, we showed that Dictyochloropsis clade 2 individuals are shared among different fungal hosts in communities of lichens of the Lobariaceae. As for other green algal lineages, there is a high amount of cryptic diversity in Dictyochloropsis. Furthermore, co-evolution between Dictyochloropsis clade 2 algae and representatives of the Lobariaceae is manifested at the community level, with several unrelated fungal species being horizontally connected by shared photobiont clones.

Microclimatic differentiation of gene pools in the Lobaria pulmonaria symbiosis in a primeval forest landscape.

Population genetics of the tree-colonizing lichen Lobaria pulmonaria were studied in the largest primeval beech forest of Europe, covering 10 000 ha. During an intensive survey of the area, we collected 1522 thallus fragments originating from 483 trees, which were genotyped with eight mycobiont- and 14 photobiont-specific microsatellite markers. The mycobiont and photobiont of L. pulmonaria were found to consist of two distinct gene pools, which are co-existing within small areas of 3-180 ha in a homogeneous beech forest. The small-scale distribution pattern of the symbiotic gene pools show habitat partitioning of lineages associated with either floodplains or mountain forests. Using approximate Bayesian computation (ABC), we dated the divergence of the two fungal gene pools of L. pulmonaria as the Early Pleistocene. Both fungal gene pools survived the Pleistocene glacial cycles in the Carpathians, although possibly in climatically different refugia. Fungal diversification prior to these cycles and the selection of photobionts with different altitudinal distributions explain the current sympatric, but ecologically differentiated habitat partitioning of L. pulmonaria. In addition, the habitat preferences of the mycobiont are determined by other factors and are rather independent of those of the photobiont at the landscape level. The distinct gene pools should be considered evolutionarily significant units and deserve specific conservation priorities in the future, for example gene pool A, which is a Pliocene relict.

Propagule size is not a good predictor for regional population subdivision or fine-scale spatial structure in lichenized fungi.

Propagule size has important consequences on the genetic structure of wind-dispersed species, as species with small propagules have higher capability of long-distance dispersal. Here, we studied reproductive modes and compared local and regional population structures in three Macaronesian lichenized fungi differing in propagule size. First, we quantified size distribution of propagules in each species. Second, genotype simulations based on microsatellite data were used to infer the reproductive mode. Third, using spatial analysis and population genetic approaches, we quantified the local and regional scale genetic structures of the fungal species. The three species differed in size distributions of propagules. The majority of populations exhibited clonal reproductive mode. Identical reproductive modes occurred often across species in the same sites, implying a possible relationship between reproductive mode and local site conditions. Contrary to expectation, at the local scale, the species exhibited similar patterns of spatial autocorrelation in genotypes. However, in agreement with the expectation based on propagule size, the species with highest frequency of small vegetative propagules (L. pulmonaria) exhibited lowest regional genetic differentiation. Nevertheless, altogether, our results show that propagule size is not a good predictor of population subdivision in lichenized fungi, neither at local nor regional spatial scale.

Characterization of fungus-specific microsatellite markers in the lichen fungus Usnea subfloridana (Parmeliaceae).

PREMISE OF THE STUDY: Microsatellite loci were developed for the haploid lichenized fungal species Usnea subfloridana to study its population subdivision and the species' response to forest disturbance, fragmentation, and environmental pollution. • METHODS AND RESULTS: We developed 14 polymorphic microsatellite markers using 454 pyrosequencing data of U. subfloridana. The number of alleles per locus ranged from three to 15, and Nei's unbiased gene diversity averaged over nine markers without null alleles ranged from 0.64 to 0.67. Evaluation of the cross-species amplification in U. glabrescens and U. wasmuthii indicates that these markers are also informative in other Usnea species. • CONCLUSIONS: These markers will allow us to investigate the effects of forest management and environmental pollution on genetic population structure of U. subfloridana and closely related species. Moreover, they will help facilitate phylogeographic studies of U. subfloridana across the species' distribution area in Europe.