Selection of algal genotypes by three species of lichen fungi in the genus Cladonia

Abstract

The lichen-forming fungal genus Cladonia P. Browne associates with green algae in the genus Trebouxia de Puymaly. Genetic structure of the algal symbionts in Cladonia gracilis (L.) Willd., Cladonia multiformis G. Merr., and C. rangiferina (L.) Nyl. was used to infer geographic patterns and symbiont associations. Algal genotypes were defined by restriction fragment length polymorphisms in the nuclear internal transcribed spacer rDNA from 115 samples of Cladonia collected from two geographic regions in Manitoba, Canada. Results suggested that two species of fungal symbiont were highly selective of the algal partner within given geographic areas, and one species was highly selective of the algal partner regardless of the geographic region. Different degrees of selectivity in three species suggested that even within the same genus, fungal selection for the algal partner may vary. In addition, DNA sequences from a subsample of 20 algal and 11 fungal specimens were used to determine phylogenetic relationships of each symbiont. Sequences of four group I intron-like insertions in the small subunit rDNA, two of which were newly reported for the genus Cladonia, were used to infer the fungal phylogeny. The intron phylogenies produced monophyletic species. Sequences of the internal transcribed spacer rDNA were used to infer the algal phylogeny. Cladonia gracilis and C. rangiferina were associated with three species of Trebouxia.