Monophyly of some North American species ofRamalinaand inferred polyketide synthase gene function

Abstract

Ramalina thrausta (Ach.) Nyl., Ramalina roesleri (Hochst. Ex Schaerer) Hue, and Ramalina dilacerata (Hoffm.) Hoffm. are three common North American species that have not been placed in a phylogeny and are sympatric in their distribution leading to uncertainty about monophyly. Species characters include secondary metabolites (polyketides) in Ramalina that may be both hereditary and influenced by environmental conditions, but little is known about the function of polyketide synthase (PKS) genes. The main goal of this study was to examine the monophyly among some of the more common species in northern North America and secondarily to compare potential PKS gene function with the phylogeny. Nucleotide sequences of two genes, the internal transcribed spacer 1 of ribosomal DNA and the mitochondrial small subunit, were used to infer a phylogeny. Gene function was inferred from three PKS genes by the ratio of nonsynonymous to synonymous substitutions (dN:dS) ratios. Although seven species of Ramalina are highly supported in monophyletic clades, two other species form clusters with low support: Ramalina americana Hale is paraphyletic, and Ramalina pollinaria (Westr.) Ach. is polyphyletic. Three PKS genes were inferred to be functional but were not present in all samples. Functional PKS genes could enable adaptation to new habitats and facilitate species diversification.