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Bryological and Lichenological Section/ABLS

OBrien, Heath [1], Jolanta, Miadlikowska [1], François, Lutzoni [1].

Comparing Fungal and Cyanobacterial Population Structures in the Lichen Symbiosis.

Comparisons of DNA sequence data from lichen fungi and their photosynthetic partners is increasing our understanding of how the populations of each partner are structured by specificity and selectivity, but there have been few comparisons of the spatial population structure of the partners. Lichens of the genus Peltigera associate with members of the cyanobacterial genus Nostoc, either as the primary photosynthetic partner (photobiont), or as a secondary photobiont restricted to cephalodia in species that primarily associate with green algae. We have sampled multiple individuals of seven Peltigrea species from nested spatial scales ranging from one meter sample plots to continental scales and sequenced a number of cyanobacterial (16S rDNA, trnL, rbcLX, rpoC2) and fungal (ITS rDNA, actin, EF1-?) markers to characterize the population structures of both partners for each species. We have analyzed these data in the context of a broader phylogeny of the genus Peltigera and of free-living and symbiotic strains of Nostoc, and other cyanobacterial genera. With the exception of P. malacea, which is specialized on a distinct lineage of Nostoc throughout its range, all Peltigera species examined share the same pool of photobiont genotypes. This photobiont pool exhibits very little genetic diversity within sites, but high levels of inter-population differentiation at spatial scales > 50 km. In contrast, the same fungal genotypes were often recovered from distant sites, indicating that gene flow is higher for lichen fungi than for their photosynthetic partners. This asymmetry may indicate that opportunities for coevolution are rare in the lichen symbiosis and suggests that photobiont diversity is greater than has previously been appreciated based on surveys conducted within limited geographic areas.

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1 - Duke University, Department of Botany, Box 90338, Durham, North Carolina, 27708-0338, USA

population structure

Presentation Type: Oral Paper
Session: 15-9
Location: Salon A - Gov Ballroom/Hilton
Date: Monday, August 15th, 2005
Time: 4:00 PM
Abstract ID:472

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