Paula T. DePriest

Algal switching among lichen symbioses

Lichens are intimate and long-term symbioses of algae and fungi. Such intimate associations are often hypothesized to have undergone long periods of symbiotic interdependence and coevolution. However, coevolution has not been rigorously tested for lichen associations. In the present study we compared the nuclear internal transcribed spacer (ITS) phylogenies of algal and fungal partners from 33 natural lichen associations to test two aspects of coevolution, cospeciation and parallel cladogenesis. Since statistically significant incongruence between symbiont phylogenies rejected parallel cladogenesis and minimized cospeciation events, we conclude that switching of highly selected algal genotypes occurs repeatedly among these symbiotic lichen associations.

A nomenclature for fungal PCR primers with examples from intron-containing SSU rDNA

AbstractWe present a compilation of polymerase chain reaction primers (oligonucleotides) used to amplify and sequence the small subunit of nuclear ribosomal DNA. To simplify use of these primers we...

DNA isolation from lichen ascomata

Analysis of DNA from the fungal component of lichens requires selective protocols to isolate its DNA from that of its symbiotic partner. In the present study, we describe a method for extraction of DNA from fungal ascomata, a source of algal-free mycelium. This method, which includes a DNA precipitation onto glassmilk (= ground SiO 2 ), is particularly useful for limited amounts of starting material, as exemplified by the isolation of DNA from ascomata of Arthonia molendoi growing parasitically on the lichen Xanthoria elegans . The protocol is effective for the isolation of high-quality DNA from cultured fungi, herbarium specimens and lichens high in polysaccharide content. This new protocol makes possible the examination of many fungi until now thought intractable to DNA methods.

Small subunit rDNA variation in a population of lichen fungi due to optional group-I introns

A natural population of the lichen-forming ascomycetous fungus, Cladonia chlorophaea, contained individuals with small subunit ribosomal DNA (SSU rDNA) of at least four different size classes and nine restriction-site patterns. The source of these differences was the variable occurrence of 200-400-nucleotide insertions, previously identified as small group-I introns, at five different positions within the SSU coding region. By specific amplification of the sequences flanking these five intron positions with the polymerase chain reaction (PCR), a minimum of nine types of rDNA repeats were defined that differ in number, position, restriction pattern and size of introns. The positions of the introns were verified by sequence analysis. The variable distribution of these introns suggests that they are currently mobile--either by intron insertion, deletion or both--within this species complex.

Strong fungal specificity and selectivity for algal symbionts in Florida scrub Cladonia lichens

Symbiosis is a major theme in the history of life and can be an important force driving evolution. However, across symbioses, it is difficult to tease apart the mechanisms that structure the interactions among potential partners. We used genetic similarity and frequency‐based methods to qualitatively and quantitatively examine the patterns of association among several co‐occurring Cladonia lichen fungi and their algal photobionts in six disjunct Florida scrub sites. The patterns of association were described by the degree of specificity, i.e. the phylogenetic range of associated partners, and of selectivity, i.e. the frequency of association among partners. Six fungal species associated with only one algal internal transcribed spacer clade, with the remaining two fungi being associated with two algal clades. In all cases, the fungi associated in unequal frequencies with the observed algal photobiont genotypes within those clades — suggesting that both specificity and selectivity were higher than expected. Fungal species can be grouped into three significantly different specificity classes: photobiont specialists, intermediates and generalists. In contrast to the pronounced specificity for photobionts among fungal species, the different Florida scrub sites do not harbour distinct photobiont pools, and differential photobiont availability cannot explain the patterning of lichen associations at this spatial scale. Therefore, we conclude that fungal specificity and selectivity for algal photobionts are major factors in determining the local composition of symbiotic partnerships.

A small insertion in the SSU rDNA of the lichen fungusArthonia lapidicola is a degenerate group-I intron

Insertions of less than 100 nt occurring in highly conserved regions of the small subunit ribosomal DNA (SSU rDNA) may represent degenerate forms of the group-I introns observed at the same positions in other organisms. A 63-nt insertion at SSU rDNA position 1512 (relative to theEscherichia coli SSU rDNA) of the lichen-forming fungusArthonia lapidicola can be folded into a secondary structure with two stem loops and a pairing of the insertion and flanking sequences. The two stem loops may correspond to the P1 and P2, and the insertion-flanking pairing to the P10, of a group-I intron. Considering these small insertions as degenerate introns provides important clues to the evolution and catalytic function of group-I introns.

Molecular Innovations in Lichen Systematics: The Use of Ribosomal and Intron Nucleotide Sequences in the Cladonia chlorophaea Complex

In the mycobiont of the Cladonia chlorophaea complex, length variation in the ribo- somal DNA is explained, in part, by the variable occurrence of multiple group I introns that may have been mobile during the evolution of this group. These potentially mobile introns can serve as a model for examining the variation detected in the ribosomal DNA from other lichens and, perhaps, as a model for examining variation in other genes, genotypes, and phenotypes. Because group I introns have been found also in the ribosomal DNA of some green algae, lichens may provide a good system to search for evidence of intron transfer between distantly related organisms. Not only can molecular systematics change the way we look at lichens, but lichens may change the way we look at molecular evolution.

SMALL INSERTIONS AT A SHARED POSITION IN THE SSU RDNA OF LECANORALES (LICHEN-FORMING ASCOMYCETES)

Abstract Small insertions are reported from the SSU rDNA of the genera Cladonia, Cladina, Stereocaulon, Pertusaria and Physcia (lichen-forming Lecanorales, Ascomycetes). The insertions range in length from 56 to 81 nucleotides, and occur at a shared position, 330 (relative to Escherichia coli), in a semi-conserved region of the SSU rDNA. These small insertions have a simple secondary structure with two stem-loops, and may represent degenerate group-I introns. Species of the same genus often have small insertions of similar lengths, secondary structures and sequences. These similarities suggest that the insertions are homologous and can provide phylogenetic information to support current classifications. Variable sequences of rDNA, such as the small insertions and group-I introns, may be powerful tools for resolving evolutionary relationships among genera and species.

Marchandiomyces lignicola sp. nov. shows recent and repeated transition between a lignicolous and a lichenicolous habit

The anamorphic basidiomycete genus Marchandiomyces presently includes two common lichenicolous (lichen-inhabiting) species, M. corallinus and M. aurantiacus (teleomorph Marchandiobasidium aurantiacum). We describe here a new species, M. lignicola sp. nov., that is similar to M. corallinus in the colour of its sclerotia, but differs in having a wood-inhabiting (lignicolous) habit. The phylogenetic position of this lignicolous fungus was compared with the lichenicolous species of Marchandiomyces and related species currently placed in the basidiomycetous families Corticiaceae and Ceratobasidiaceae using parsimony, likelihood, and Bayesian analyses of complete sequences of the nuclear small subunit and internal transcribed spacers ribosomal DNA, and a portion of the nuclear large subunit ribosomal DNA. These DNA sequences were obtained from isolated cultures of freshly collected specimens. Significant Bayesian posterior probabilities, as well as maximum likelihood and parsimony analyses, indicate that the new lignicolous species is closely related to M. corallinus, the type species of Marchandiomyces. In most analyses these two species are monophyletic with the lichenicolous M. aurantiacus, although this relationship is not strongly supported. Since M. lignicola is more closely related to M. corallinus than to M. aurantiacus, either a transition to the lignicolous habit occurred recently within an ancestral lichenicolous group or, more likely, transition to the lichenicolous habit arose recently and in parallel from an ancestral lignicolous habit.

A review of the International Code of Botanical Nomenclature with respect to its compatibility with phylogenetic classification

3 Hunt Institute.for Botanical Documentation, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, U.S.A. rkiger@andrew.cmu.edu 4 Royal Botanic Garden, Edinburgh, EH3 5LR, Scotland, U.K. jmcneill@rbge.org.uk 5 Brooklyn Botanic Garden, 1000 Washington Avenue, Brooklyn, New York 11225, U.S.A. gerrymoore@bbg. org (author for correspondence) 6 The New York Botanical Garden, Bronx, New York 10458 U.S.A. dws@nybg.org 7Division of Environmental Biology, National Science Foundation, 4201 Wilson Boulevard, Arlington, Virginia 22230, U.S.A. qwheeler@nsfgov