Genetic diversity of the photobiont of the bipolar lichen-forming ascomycete Xanthomendoza borealis

The objective of this study was to analyse the genetic diversity in the symbiotic partner (photobiont) of the bipolar lichen-forming ascomycete Xanthonzendoza borealis. We also examined whether the mycobiont's photobiont choice could shed light on the origin of the bipolar geographic distribution. Twenty-seven new sequences of the partial ITS1 - 5.8S - partial ITS2 (ITS) of the photobiont of X. borealis were analysed. The molecular marker identifies the photobiont as the unicellular green alga Trebouxia. A total of 18 haplotypes were recovered. Genetic diversity and haplotype richness levels of the photobiont are lower in Antarctica than in regions of the northern hemisphere. Xanthomendoza borealis has the ability to use algae from at least three phylogenetic lineages of the genus Trebouxia as photobiont, that is, expresses low selectivity. The 'photobiont-pool' seems to be shared with several other lichen-forming ascomycetes, for example, species of Cetraria, Flavocetraria, Lecidea and Rinodina. This supports the hypothesis that lichen-forming fungi especially in harsh climates have a strategy of low selectivity.