Specialization patterns in symbiotic associations: A community perspective over spatial scales

Abstract

Specialization, contextualized in a resource axis of an organism niche, is a core concept in ecology. In biotic interactions, specialization can be determined by the range of interacting partners. Evolutionary and ecological factors, in combination with the surveyed scale (spatial, temporal, biological, and/or taxonomic), influence the conception of specialization. This study aimed to assess the specialization patterns and drivers in the lichen symbiosis, considering the interaction between the principal fungus (mycobiont) and the associated Nostoc (cyanobiont), from a community perspective considering different spatial scales. Thus, we determined Nostoc phylogroup richness and composition of lichen communities in 11 Nothofagus pumilio forests across a wide latitudinal gradient in Chile. To measure specialization, cyanobiont richness, Simpson's and d′ indices were estimated for 37 mycobiont species in these communities. Potential

Cyanobacterial Variability in Lichen Cephalodia

“…When comparing specialization between bi-membered (cyanolichens and chlorolichens) and tri-membered (cephalolichens) lichen species, several patterns have been found. A high specialization hypothesized for cephalolichens [ 28 ] differed from the results of [ 20 ], showing that cephalolichens are more generalized than cyanolichens, and from other studies, which found no differences between both [ 25 , 29 ]. At the intrathalline (individual) level, and concerning cephalolichens specifically, it has been shown that most tripartite lichens contain the same Nostoc strain in all cephalodia of individual thalli [ 28 ], with the exception of Peltigera venosa , Lobaria pulmonaria , and three species of Pannaria ( P. farinosa , P. sphinctrina , and P. lobulifera ), which housed different cyanobionts in different cephalodia [ 23 , 30 , 31 ].…”

“…Two forests from a previous study carried out in Chile and sampled between 2017 and 2018 were used (Parque Nacional Torres del Paine and Isla Navarino) [ 20 ]. Forest stands were mostly formed by Notofagus pumilio with over 65% of cover.…”

“…While there are different attributes to characterize specialization in biotic interactions, the classification of organisms as specialists or generalists has been mostly based on the number of interacting partners [ 13 , 14 ]; however, see [ 15 ]. The variability in the photobiont partner is, thus, related to the specialization of the mycobiont for the photobiont and may be observed at different levels (biological, geographical, or ecological) [ 10 , 16 , 17 , 18 , 19 , 20 ]. At the biological level (individual, species, or genus levels), numerous studies have shown contrasting patterns: from a high specialization of mycobiont towards the photobiont, i.e., [ 11 , 21 , 22 , 23 , 24 ], to a common pattern of generalization (i.e., a high number of interacting photobionts) [ 25 , 26 , 27 ].…”

“…On the other hand, factors driving photobiont selection are diverse and related to phylogenetic relationships, reproductive strategy, the availability of photobionts, or ecological factors [ 12 , 18 , 24 , 29 , 36 , 39 , 40 , 41 , 42 ]. In a recent study, the authors showed that photobiont availability, the function of the cyanobiont (principal photobiont for cyanolichens or secondary photobiont for cephalolichens), and the mycobiont species were factors related with specialization in cyanobacterial lichens [ 20 ].…”

Myco–Phycobiont Interactions within the “Ramalina farinacea Group”: A Geographical Survey over Europe and Macaronesia

“…Because previous studies have shown that lichen-forming fungi tend to preferentially select photobiont lineages which are better adapted to local environmental conditions [ 18 , 19 , 20 , 21 , 22 , 23 ], we will here test the following hypotheses: (i) mycobionts in the R. farinacea group associate differentially with phycobionts in Macaronesia and Mediterranean, temperate, and Boreal regions in Europe; and (ii) the association with different phycobionts shapes the ecological distribution of the mycobionts. In doing this, we will investigate the complexity of interactions among mycobiont and phycobiont lineages, the degree of specificity across their geographic distributions [ 24 , 25 , 26 ], and the climatic niche width of the primary phycobionts.…”