Domestication of algae by lichen-forming fungi describes the symbiotic relationship between the photosynthetic (green alga or cyanobacterium; photobiont) and fungal (mycobiont) partnership in lichen associations (Goward 1992). The algal domestication implies that the mycobiont cultivates the alga as a monoculture within its thallus, analogous to a farmer cultivating a food crop. However, the initial photobiont 'selection' by the mycobiont may be predetermined by the habitat rather than by the farmer. When the mycobiont selects a photobiont from the available photobionts within a habitat, the mycobiont may influence photobiont growth and reproduction (Ahmadjian & Jacobs 1981) only after the interaction has been initiated. The theory of ecological guilds (Rikkinen et al. 2002) proposes that habitat limits the variety of photobionts available to the fungal partner. While some studies provide evidence to support the theory of ecological guilds in cyanobacterial lichens (Rikkinen et al. 2002), other studies propose models to explain variation in symbiont combinations in green algal lichens (Ohmura et al. 2006; Piercey-Normore 2006; Yahr et al. 2006) hypothesizing the existence of such guilds. In this issue of Molecular Ecology, Peksa & Škaloud (2011) test the theory of ecological guilds and suggest a relationship between algal habitat requirements and lichen adaptation in green algal lichens of the genus Lepraria. The environmental parameters examined in this study, exposure to rainfall, altitude and substratum type, are integral to lichen biology. Lichens have a poikilohydric nature, relying on the availability of atmospheric moisture for metabolic processes. Having no known active mechanism to preserve metabolic thallus moisture in times of drought, one would expect a strong influence of the environment on symbiont adaptation to specific habitats. Adaptation to changes in substrata and its properties would be expected with the intimate contact between crustose lichens in the genus Lepraria. Altitude has been suggested to influence species distributions in a wide range of taxonomic groups. This is one of the first studies to illustrate an ecological guild, mainly for exposure to rainfall (ombrophiles and ombrophobes), with green algal lichens.
Symbiotic interactions are widespread in nature, but the relationship between life history, fecundity, and habitat specificity has been underexplored. This study investigated the life history strategies of foliose saxicolous lichens relative to their surrounding communities. Macrolichens were collected from 39 transects in Manitoba and Ontario. Frequency and percentage of ground cover of macrolichens, environmental variables, and numbers of apothecia and ascospores were recorded. Lichen assemblages were characterized using species similarity in a cluster analysis and ordination methods and were defined into communities using analysis of variance of the biotic variables among assemblages. Lichen life history strategies were inferred from community features, lichen fecundity, and morphological features. The general linear model determined which environmental variables may have influenced fecundity. The 81 species of macrolichens present in three lichen communities differed in species richness, with low species richness in the open mossy rock community, moderate in the grassy rock community, and high in the treed rock community. Three foliose saxicolous lichens dominated particular communities, and the life history strategy was characterized as competitive for Arctoparmelia centrifuga (L.) Hale, stress tolerant for Xanthoparmelia viriduloumbrina (Gyel.) Lendemer, and ruderal generalist for Xanthoparmelia cumberlandia (Gyel.) Hale. The proportion of sexual and asexual reproductive propagules for macrolichens showed uniformity between communities despite a significant difference in species richness. The study provides insights into the ecology of saxicolous lichens growing in the boreal forest and a characterization of lichen communities, and it shows how morphologically similar lichens can exhibit different life history strategies.
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