Presentation Detail

SSB Symposium: Ernst Mayr Symposium

Magain, Nicolas [1], Lutzoni, Francois [2], Rivas Plata, Eimy [2], Goffinet, Bernard [3], Sérusiaux, Emmanuël [1], Miadlikowska, Jolanta  [2].

Evolution of specificity in fungi-cyanobacteria lichen symbioses.

Variation in levels of specificity among symbiotic partners is key to a comprehensive understanding of the evolution of symbiotic systems. This variation is expected to occur at all spatio-temporal scales within species as well as within a broad inter-species phylogenetic framework. We assessed the level of specificity of the lichen-forming ascomycete fungus Peltigera (mycobiont) and its cyanobacterial partner Nostoc (cyanobiont), where the latter is believed to be predominantly transmitted horizontally. We inferred the phylogeny of the cosmopolitan and monophyletic section Polydactylon of the mycobiont, based on five nuclear loci, and of their cyanobionts, using the rbcLX region. We sequenced the genomic DNA of the mycobiont and cyanobiont of 208 lichen thalli, representing 33 putative lichen-forming fungal species sampled worldwide. Our main goal was to determine the level of specificity of each partner of this highly stable symbiosis, within a phylo-biogeographical framework. We found a broad spectrum of specificity for both partners ranging from strict specialists to generalists. The distribution of Nostoc and Peltigera seem to be strongly shaped by climate as well as by limitations on their long-distance dispersal abilities. The dominant trend observed was one where mycobionts are more specialized, i.e., associating mostly with one or few Nostoc phylotypes (even when several other phylotypes are available through their associations with neighboring Peltigera species), than cyanobionts, which are generalists, i.e., associating frequently with several Peltigera species. Mycobiont species resulting from recent speciation events, which seem to be associated with the colonization of a new biogeographical area, switched to a generalist selection of cyanobionts, while specialization of the mycobiont seems to be favored in areas where species have been established for long periods of time. Specialization of the mycobiont seems to be correlated with a decrease in its genetic variation, while acquisition of a "new"� Nostoc phylotype (cyanobiont switch) might be one of the mechanisms leading to adaptive radiations by the mycobiont, and to the expansion of the mycobiont distribution to new environments. Overall,our results are in partial agreement with Law and Lewis' paradigm of mutualistic interactions, the Red King and the Geographic Mosaic of Coevolution hypotheses.

1 - University of Liege, Biology, ecology and evolution, Boulevard du rectorat 27, Liège, 4000, Belgium
2 - Duke University, Department of Biology, Box 90338, Durham, NC, 27708, USA
3 - University Of Connecticut, Department Of Ecology & Evolutionary Biology, 75 N. Eagleville Road, U-3043, STORRS, CT, 06269-3043, USA
4 - University of Liege, Biology, ecology and evolution, Boulevard du rectorat 27, Liège, 4000, Belgium

Keywords:
lichen-forming fungi
nostoc
Peltigera
horizontal transmission
specificity
generalist
specialist
phylogeny
biogeography.

Presentation Type: Symposium Presentation
Session: 212
Location: Ballroom 2/Cliff Lodge
Date: Sunday, June 23rd, 2013
Time: 11:00 AM
Number: 212003
Abstract ID:1162
Candidate for Awards:Ernst Mayr Award