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

Hill, David J.

doi:10.1007/s12229-009-9028-x

Cited by 28 publications

(15 citation statements)

References 48 publications

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“…In many other lichen fungi, sexual reproductive mode has been reported (Arnerup et al 2004;Högberg et al 2002;Kroken and Taylor 2001;Werth and Sork 2008). Our finding of photobiont clonality is consistent with the concept that photobionts do not undergo sexual reproduction when in the lichen thallus (Ahmadjian 1993;Friedl and Büdel 1996;Hill 2009); thus far, only one study has reported evidence for sexual photobiont populations (Kroken and Taylor 2000).…”

Section: Discussionsupporting

confidence: 90%

Congruent Genetic Structure in the Lichen-Forming Fungus Lobaria pulmonaria and Its Green-Algal Photobiont

Werth¹,

Scheidegger²

2012

MPMI

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The extent of codispersal of symbionts is one of the key factors shaping genetic structures of symbiotic organisms. Concordant patterns of genetic structure are expected in vertically transmitted symbioses, whereas horizontal transmission generally uncouples genetic structures unless the partners are coadapted. Here, we compared the genetic structures of mutualists, the lichen-forming fungus Lobaria pulmonaria and its primary green-algal photobiont, Dictyochloropsis reticulata. We performed analysis of molecular variance and variogram analysis to compare genetic structures between symbiosis partners. We simulated the expected number of multilocus-genotype recurrences to reveal whether the distribution of multilocus genotypes of either species was concordant with panmixia. Simulations and tests of linkage disequilibrium provided compelling evidence for the codispersal of mutualists. To test whether genotype associations between symbionts were consistent with randomness, as expected under horizontal transmission, we simulated the recurrence of fungal-algal multilocus genotype associations expected by chance. Our data showed nonrandom associations of fungal and algal genotypes. Either vertical transmission or horizontal transmission coupled with coadaptation between symbiont genotypes may have created these nonrandom associations. This study is among the first to show codispersal and highly congruent genetic structures in the partners of a lichen mutualism.

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Section: Discussionsupporting

confidence: 90%

Congruent Genetic Structure in the Lichen-Forming Fungus Lobaria pulmonaria and Its Green-Algal Photobiont

Werth¹,

Scheidegger²

2012

MPMI

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“…Hill (2009) recently postulated that ‘the mycobiont may acquire [photobiont] strains (species, varieties, forms or genotypes) that are more suitable than others but this is unlikely to have any evolutionary consequences.’ The ability to associate with ecotypically differentiated and locally adapted photobionts would clearly be an evolutionary advantage for a mycobiont and may explain the wide ecological amplitudes of many lichen species.…”

Section: Discussionmentioning

confidence: 99%

Population structure of mycobionts and photobionts of the widespread lichen Cetraria aculeata

et al. 2011

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Lichens are symbioses between fungi (mycobionts) and photoautotrophic green algae or cyanobacteria (photobionts). Many lichens occupy large distributional ranges covering several climatic zones. So far, little is known about the large-scale phylogeography of lichen photobionts and their role in shaping the distributional ranges of lichens. We studied south polar, temperate and north polar populations of the widely distributed fruticose lichen Cetraria aculeata. Based on the DNA sequences from three loci for each symbiont, we compared the genetic structure of mycobionts and photobionts. Phylogenetic reconstructions and Bayesian clustering methods divided the mycobiont and photobiont data sets into three groups. An amova shows that the genetic variance of the photobiont is best explained by differentiation between temperate and polar regions and that of the mycobiont by an interaction of climatic and geographical factors. By partialling out the relative contribution of climate, geography and codispersal, we found that the most relevant factors shaping the genetic structure of the photobiont are climate and a history of codispersal. Mycobionts in the temperate region are consistently associated with a specific photobiont lineage. We therefore conclude that a photobiont switch in the past enabled C. aculeata to colonize temperate as well as polar habitats. Rare photobiont switches may increase the geographical range and ecological niche of lichen mycobionts by associating them with locally adapted photobionts in climatically different regions and, together with isolation by distance, may lead to genetic isolation between populations and thus drive the evolution of lichens.

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“…The genetic structure of a lichen population will be strongly influenced by the manner in which photobionts are dispersed and transmitted to the fungus (Hill 2009). Vertical (or co‐dependent) transmission occurs when the photobiont disperses as part of the vegetative propagule of the lichen, thus presumably representing the predominant process in exclusively or nearly exclusively asexual lichen species (Werth & Sork 2010).…”

Section: Introductionmentioning

confidence: 99%

Vertical and horizontal photobiont transmission within populations of a lichen symbiosis

et al. 2012

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Lichens are widespread symbioses and play important roles in many terrestrial ecosystems. The genetic structure of lichens is the result of the association between fungal and algal populations constituting the lichen thallus. Using eight fungus- and seven alga-specific highly variable microsatellite markers on within-population spatial genetic data from 62 replicate populations across Europe, North America, Asia and Africa, we investigated the contributions of vertical and horizontal transmission of the photobiont to the genetic structure of the epiphytic lichen Lobaria pulmonaria. Based on pairwise comparisons of multilocus genotypes defined separately for the mycobiont and for the photobiont, we inferred the transmission mode of the photobiont and the relative contribution of somatic mutation and recombination. After constraining the analysis of one symbiont to pairs of individuals with genetically identical symbiotic partners, we found that 77% of fungal and 70% of algal pairs were represented by clones. Thus, the predominant dispersal mode was by means of symbiotic vegetative propagules (vertical transmission), which dispersed fungal and algal clones co-dependently over a short distance, thus shaping the spatial genetic structure up to distances of 20m. Evidence for somatic mutation generating genetic diversity was found in both symbionts, accounting for 30% of pairwise comparisons in the alga and 15% in the fungus. While the alga did not show statistically significant evidence of recombination, recombination accounted for 7.7% of fungal pairs with identical algae. This implies that, even in a mostly vegetatively reproducing species, horizontal transmission plays a role in shaping the symbiotic association, as shown in many coral and other symbioses in nature.

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

Cited by 28 publications

References 48 publications

Congruent Genetic Structure in the Lichen-Forming Fungus Lobaria pulmonaria and Its Green-Algal Photobiont

Congruent Genetic Structure in the Lichen-Forming Fungus Lobaria pulmonaria and Its Green-Algal Photobiont

Population structure of mycobionts and photobionts of the widespread lichen Cetraria aculeata

Vertical and horizontal photobiont transmission within populations of a lichen symbiosis

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