The complexity of symbiotic interactions influences the ecological amplitude of the host: A case study inStereocaulon(lichenized Ascomycota)

Abstract

Symbiosis plays a fundamental role in nature. Lichens are among the best known, globally distributed symbiotic systems whose ecology is shaped by the requirements of all symbionts forming the holobiont. The widespread lichen-forming fungal genus Stereocaulon provides a suitable model to study the ecology of microscopic green algal symbionts (i.e., phycobionts) within the lichen symbiosis. We analysed 282 Stereocaulon specimens, collected in diverse habitats worldwide, using the algal ITS rDNA and actin gene sequences and fungal ITS rDNA sequences. Phylogenetic analyses revealed a great diversity among the predominant phycobionts. The algal genus Asterochloris (Trebouxiophyceae) was recovered in most sampled thalli, but two additional genera, Vulcanochloris and Chloroidium, were also found. We used variation-partitioning analyses to investigate the effects of climatic conditions, substrate/habitat characteristic, spatial distribution and mycobionts on phycobiont distribution. Based on an analogy, we examined the effects of climate, substrate/habitat, spatial distribution and phycobionts on mycobiont distribution. According to our analyses, the distribution of phycobionts is primarily driven by mycobionts and vice versa. Specificity and selectivity of both partners, as well as their ecological requirements and the width of their niches, vary significantly among the species-level lineages. We demonstrated that species-level lineages, which accept more symbiotic partners, have wider climatic niches, overlapping with the niches of their partners. Furthermore, the survival of lichens on substrates with high concentrations of heavy metals appears to be supported by their association with toxicity-tolerant phycobionts. In general, low specificity towards phycobionts allows the host to associate with ecologically diversified algae, thereby broadening its ecological amplitude.

Symbiosis between river and dry lands: phycobiont dynamics on river gravel bars

“…1) is congruent with previous studies (Peksa and Škaloud 2011; Gauslaa et al 2013; Škaloud et al 2015; Moya et al 2015; Vančurová et al 2018). The species boundaries delimited in Vančurová et al 2018 and nomenclature used ibidem were maintained. We recovered a total of 14 lineages, including one novel lineage here referred to as StA9.…”

“…Both algal and fungal nuclear internal transcribed spacers (ITS rDNA) and the algal actin type I gene (including one complete exon and two introns located at codon positions 206 and 248; Weber and Kabsch 1994) were PCR amplified using primers listed in Online Resource 1/Table S3. PCRs were performed as described in Vančurová et al (2018). All PCR were performed in 20 μl using Red Taq Polymerase (Sigma) as described by Peksa and Škaloud (2011) or with My Taq Polymerase.…”

“…The phylogeny of Stereocaulon alpinum showed two lineages (OTU35 and OTU2; see below). Since the mycobiont identity affects the phycobiont diversity (Vančurová et al 2018) four samples belonging to the minority species-level lineage (OTU2) were also excluded. Thus, statistical analyses were carried out using 141 members of the prevailing mycobiont species-level lineage (OTU35) and their photobiots.…”

“…Moreover, previous studies confirmed its ability to survive episodic submersion (Sadowsky et al 2012), even though it is not natively aquatic. Recently, an exceptional diversity of phycobionts was discovered to be associated with Stereocaulon , including three ecologically diversified trebouxiophycean genera Asterochloris, Vulcanochloris and Chloroidium (Vančurová et al 2015, 2018).…”

“…The lichen host ecological amplitude may be greatly influenced by its specificity towards the photobionts (Rolshausen et al 2017; Vančurová et al 2018). Symbiotic interactions vary along the environmental gradients (Godschalx et al 2019) and could be affected by stressful environments (Romeike et al 2002; Engelen et al 2010).…”