Evolution of ITS Ribosomal RNA Secondary Structures in Fungal and Algal Symbionts of Selected Species of Cladonia sect. Cladonia (Cladoniaceae, Ascomycotina)

Abstract

Evolutionary studies in lichen associations follow that of the fungal symbiont (mycobiont), which is the symbiont after which the lichen is named and forms the majority of the thallus. However, evolution of the algal partner (photobiont) is important to maintain compatibility between symbionts and to optimize productivity of the lichen association. The internal transcribed spacer (ITS) regions of the nuclear ribosomal DNA (rDNA) were examined for primary DNA sequence patterns and for patterns in the secondary structure of the rRNA transcripts in both symbionts of the genus Cladonia. Fungal and algal symbionts show opposite trends in rates of evolution and fragment lengths. Both symbionts showed stronger conservation of the ITS2 structure than the ITS1 structure. Homology was evident in the secondary structures between the two highly divergent chlorophyte and ascomycete taxonomic groups. Most fungal species and all species complexes were polyphyletic. The ITS rDNA of the natural lichen algae from Manitoba and four known algal species is highly similar. The natural lichen algae segregate into highly supported clades by environmental features, suggesting that algae that are already adapted to the environment may associate with germinating fungal propagules in the genus Cladonia. Fungal plasticity may allow the mycobiont to adapt to the environment of the photobiont producing variation in lichen morphology. This might explain the incongruence of phylogenetic patterns between the algal and fungal partners tested and the polyphyly of the fungal species.

Asymmetric Co-evolution in the Lichen Symbiosis Caused by a Limited Capacity for Adaptation in the Photobiont

“…In contrast to this study, a study of ITS in ribosomal DNA in Cladonia mycobionts and associated photobionts indicated that Trebouxia strains clustered together according to geographical location and more closely corresponded to environmental features (e.g. soil type) than fungal lineages (Beiggi & Piercey-Normore, 2007). With the recently evolved basidiolichen Omphalina, Zoller and Lutzoni (2003) concluded that the Coccomyxa strain was genetically much more uniform than the mycobiont and distinct over a wide geographical range from cultures isolated from free-living populations and the strains found in lichens belonging to the Peltigeraceae.…”

Genetic Variation of North American Triatomines (Insecta: Hemiptera: Reduviidae): Initial Divergence between Species and Populations of Chagas Disease Vector

“…Therefore, structures that retain a highly conserved configuration may be useful tools for analyzing this cryptic species. 35 Using cytB sequences, we detected low values of intraspecific similarity (86-91%) and high values of nucleotide diversity (0.09-0.14) between the Phyllosoma complex species M. longipennis, M. mazzottii, T. mexicana, and M. picturatus from different geographic areas. For example, divergence levels for several T. infestans populations in South America did not exceed 2% 36 ; Within T. rubida populations from Mexico and the United States, the percentage similarity was 87%, and within the T. recurva population, the percentage similarity was 92%.…”

Assembling the challenging puzzle of algal biodiversity: species delimitation within the genus Asterochloris (Trebouxiophyceae, Chlorophyta)

“…, , Cordeiro et al. , Nelsen and Gargas , Beiggi and Piercey‐Normore , Bačkor et al. , Kotelko and Piercey‐Normore , Škaloud and Peksa , Peksa and Škaloud , Řídká et al.…”