Bryological and Lichenological Section/ABLS
Dal-Forno, Manuela , Lawrey, James D. , Lucking, Robert .
Mycobiont cladogenesis triggered by photobiont speciation: A case study of the Rhizonema-Cora lichen symbiosis.
Based on recent phylogenetic studies of the basidiolichen clade Dictyonema s.l., 63 species are now accepted in five genera, with still hundreds of species remaining to be described. The identified photobionts of all of these species are members of a remarkable clade of cyanobacteria called Rhizonema, which may be entirely lichenized. To test this hypothesis, we obtained 16S rDNA sequences from 560 specimens representing all major clades within Dictyonema s.l., and an additional 21 ascolichens suspected to contain Rhizonema, collected from Bolivia, Brazil, Canary Islands (Tenerife), Chile, Colombia, Costa Rica, Ecuador (continental), Fiji, Galapagos Islands, Guatemala, Mascarene Islands (La Reunión), Mexico, New Zealand, Panama, Peru, Philippines, Puerto Rico, Thailand, and Venezuela. All of the samples were found to harbor the Rhizonema photobiont. Most samples presented more than one haplotype of Rhizonema, each usually represented by hundreds of reads. For the Dictyonema samples, only 4 out of the 560 did not present a secondary haplotype, and 38 had an equal number of reads for each of the haplotypes observed. Initial alignments of the sequences suggested two main clusters of Rhizonema across all specimens, and Maximum Likelihood and TCS network analyses confirmed this result. We are interpreting these as two separate lineages of Rhizonema, and each is represented by a relatively large number of haplotypes. There is no indication of photobiont-mycobiont co-evolution at the species level in any of the clades of Dictyonema s.l. However, one of the two lineages of Rhizonema appears to partner primarily (95%) with one of the Cora clades collected from northern Andean locations. The other Rhizonema lineage is represented by a much larger number of haplotypes and these appear to partner with mycobionts from many Dictyonema clades, likely representing the ancestral Rhizonema clade within these lichens. Overall, our results show that the diversity of photobionts is far lower than that of the mycobionts, a view that lends support to a previously published hypothesis concerning photobiont sharing in the clade.
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1 - George Mason University, Environmental Science and Public Policy, 4400 University Drive, Fairfax, VA, 22030, USA
2 - George Mason University, Biology, 4400 University Drive, MSN 3E1, Fairfax, VA, 22030, USA
3 - Field Museum Of Natural History, Department Of Botany, 1400 South Lake Shore Drive, Chicago, IL, 60605-2496, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Salon 10/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 2:30 PM
Candidate for Awards:A. J. Sharp Award