William Louis Culberson

Chemistry and Sibling Speciation in the Lichen-Forming Fungi: Ecological and Biological Considerations

Sibling speciation, the reproductive isolation of populations often accompanied by ecological but little or no morphological differentiation, is a common product of evolution. Although it may be widespread among the cryptogams, it is best documented from all groups of the animals andfrom the vascular plants. The ecological and biological characteristics of the major chemotypes into which many Linnean species of lichens are divided favor the interpretation of these chemotypes as sibling species rather than as components of traditional morphological species. For the lichens, examples are given of sympatric sibling speciation effected by the isolating mechanisms of a sharply telescoped environment, the bark of different trees growing together, tree bark and nearby boulders and adjacent soils of different types. An experimental approach in the lichens for determining the extent of gene flow in morphologically similar populations of mixed chemotypes is proposed.

Habitat selection by chemically differentiated races of lichens.

The maritime European lichens of the aggregate species Ramalina siliquosa represent six chemical races. Where the races are sympatric they populate different habitats. Such intensive local ecological sorting of morphologically similar individuals accumulating different, highly specialized metabolic end products appears to be unknown in other plants.

A Phylogenetic View of Chemical Evolution in the Lichens

The distribution of 209 chemical substances among the 2,315 species of lichens that have been reported in a literature of approximately 1,000 papers is summarized. The information is used to assess the extent and the nature of chemical evolution in the lichen-forming fungi and to evaluate the present supraspecific (especially generic and familial) classifications of these plants. The order Lecanorales is the seat of most of the chemical variation, especially in the secondary natural products most useful in systematics, namely the sub- stances formed by coupling of phenolic units such as the orcinol and p-orcinol compounds. Most genera and families that are well defined morphologically and appear to represent natural taxa show highly uniform chemistries of several to many biogenetically related substances or sets of substances. Many genera with chemistries discordant for the families in which they are currently classified also seem to have affinities elsewhere from morphological information. In the lichen-forming fungi, which lack a fossil record, comparative phytochemistry is the most useful independent check that exists to evaluate the naturalness of systems of classification based upon morphology.

Characteristic lichen products in cultures of chemotypes of the Ramalina siliquosa complex

Sixteen characteristic aromatic lichen products were identified in alga-free fungal cultures derived from single-spore isolates of four chemotypes of the Ramalina siliquosa species complex. The chemistries of many cultures are more complex than those of natural thalli. The compounds identified include the major f-orcinol depsidones that characterize the chemotypes as well as biogenetically reasonable precursors not yet proved in natural thalli. Single-spore progeny from natural thalli can be assigned to chemotype without being lichenized with an alga. This result simplifies the use of secondary-product chemistry as a genetic marker to assess the limits of gene flow between chemotypes in natural populations.

NMR assignments of depsides and tridepsides of the lichen family Umbilicariaceae

Abstract NMR spectral analysis provides important information for the identification of secondary products of chemotaxonomic significance in the lichen genera Umbilicaria and Lasallia (Umbilicariaceae). Two depsides (evernic and lecanoric acids) and eight tridepsides (crustinic, gyrophoric, hiascic, lasallic, 4- O -methyl-gyrophoric, ovoic and umbilicaric acids and tenuiorin) were isolated from various unrelated lichens. Seven of the ten compounds are important taxonomic characters in the family Umbilicariaceae. 1 H and 13 C NMR spectral signals were assigned for the compounds and for methyl esters of lecanoric, evernic and gyrophoric acids. Using these NMR data and mass spectrometry, chemical structures were elucidated for two new compounds, papulosic acid (2,6-dihydroxy-3-carboxy-4-methylphenyl orsellinate) from the umbilicariaceous Lasallia papulosa and deliseic acid (lecanoryl 3-acetoxy-4,6-dihydroxy-2-methylbenzoate) from the parmeliaceous Cetrariella delisei .

Thermally induced chemical artifacts in lichens

Abstract Unsuspected thermal degradation of secondary products in lichens prior to chemical study, although probably uncommon, can lead to mistaken conclusions and taxonomic error. Thermally induced artifacts were found in the chemistries of Hypotrachyna partita from a site of volcanic activity in Costa Rica and in the type of H. prolongata from Haiti that had been dried for the herbarium with heat. In the Southern Appalachian Mountains normal material of H. prolongata has been considered a chemically different species. Thermal stability of secondary products may be an important factor in the chemical evolution of lichens inhabiting extreme environments.

Analysis of chemical and morphological variation in the Ramalina siliquosa species complex

In an attempt to clarify the taxonomy of the polymorphic maritime lichens of theRamalina siliquosa group in Europe, variation was analyzed in visible and chemical characteristics of 1042 specimens from four localities (one station each in Scotland, Wales, England, and Brittany). The plants belong to six major chemical types representing a replacement series of closely related medullary depsidones. There is a broad correlation of chemical and visible traits. The narrower-lobed often basally blackened individuals (corresponding approximately to the usual concept of “R. curnowii”) produce no medullary constituents nor norstictic or stictic acids. The broader-lobed unblackened ones (corresponding approximately to the usual concept of “R. siliquosa”) produce stictic, salazinic, protocetraric, or hypoprotocetraric acids. The proportion of each chemical type in the four populations studied varies markedly. The southern (English and French) populations together contain all six chemical variants in roughly similar proportions. However, to the north, in Wales and Scotland, the populations become simpler as some chemical races drop out and salazinic acid-producing plants predominate. These findings correlate well with the general geographic distribution of the chemical variants from a study of 117 herbarium specimens. The chemically distinct plants have different amplitudes of ecologic tolerance which appear to regulate niche selection in theRamalina zone, the conspicuous vegetational belt which these lichens form above the intertidal zone on the Atlantic and Baltic coasts of Europe. The complex is interpreted as a set of six species differing to an extent by visible traits but primarily by chemical, geographical, and ecological ones. Three of the species are new:Ramalina atlantica Culb.,R. stenoclada Culb., andR. druidarum Culb. A hypothetical scheme is suggested to explain the evolutionary origin of the species recognized.

Genetic and environmental effects of growth and production of secondary compounds in Cladonia cristatella

Abstract This is the first study under controlled conditions to evaluate genetic and environmental variables acting on the whole lichen. Four cloned lines of Cladonia cristatella , derived from single spores and re-associated with teh normal algal partner ( Trebouxia erici ), were grown in a phytotron and chemically analysed. Growth, as measured by cover, was significantly affected by clone and consistently decreased at lower temperatures and at higher light intensities. The two biogenetically distinct pathways leading to the characteristic secondary products were affected differently by factors related to the genetic component (clone), the developmental stage (age) and the environment (temperature and light). Products fo the barbatic acid pathway, leading to depsides, were detected in the youngest lichenized hyphae, and the concentrations did not change significantly with age. products of the didymic acid pathway, leading to dibenzofurans, were incrasingly abundant in progressively older squamules. The four clones showed significantly different capacities for the production of compounds by the two pathways and significantly different responses to the environmental factors studied. The concentrations of compounds from the barbatic acid pathway increased at lower temperatures; those of compounds from the didymic acid pathway either changed little or decreased appreciably according to clone. Of the factors studied, light had the least effect on chemistry. Between-pathway variation in production of secondary products was greater than within-pathway variation.

Orcinol-type Depsides and Depsidones in the Lichens of the Cladonia chlorophaea Group (Ascomycotina, Cladoniaceae)

Five new lichen products-the depsidones stenosporonic and divaronic acids and the meta-depsides hyperhomosekikaic, submerochlorophaeic, and subpaludosic acids--are reported from species of the Cladonia chlorophaea group and from the genera Neofuscelia, Parmelia, Ramalina and Physcidia. These compounds fill previously vacant positions in four chemically homologous series of depsidones and meta-depsides involving 3- and 5-carbon sidechains. The chemical struc- tures are based upon chromatographic correlations, and those of the depsidones are confirmed by mass spectrometry. In the lichen fungi natural-product variation is so closely correlated with morphological variation that chemical characters have been intimately involved in systematics for more than a century. In general, each morphotype is chemically constant throughout its range and upon all substrates. Chemistry con- sequently becomes a key character in even routine taxonomic identifications. In some morphotypes, however, multiple chemical races have evolved, producing a noncongruence of chemistry and form that is the source of controversy regarding the sig- nificance of natural-product variation as a marker of evolutionary divergence. Most chemically vari- able morphotypes consist of only a few chemotypes that may be characterized by biosynthetically closely related compounds. There are, however, a few ex- amples of morphs with many chemical races rep- resenting a broad spectrum of biosynthetic differ- ences. An analysis of morphotypes with such extensive chemical diversity should lead to an eval- uation of the relative significance of levels of chem- ical divergence. The Cladonia chlorophaea group, in the broadest sense in which this name has been applied, offers one of the most complex examples of natural-prod- uct differentiation among the lichen-forming fungi. In its worldwide distribution, which includes all continents except Antarctica, it consists of at least 14 major chemotypes. Its remarkable chemical di- versity involves some 35 secondary products dis- tributed among four major categories: 1) orcinol- type para-depsides, meta-depsides and depsidones; 2) a 3-orcinol para-depside and 3-orcinol depsi- dones; 3) the unique aliphatic ester bourgeanic acid;

The Genera Cetrariastrum and Concamerella (Parmeliaceae): A Chemosystematic Synopsis

The pantropical genus Cetrariastrum (= Everniastrum Hale) has its center of diversity in the highlands of northern South America and of Mesoamerica but it also occurs in the mountains of southern Africa and southern Asia. It was probably differentiated in Gondwanaland, but tropical-island disjunctions reveal the efficacy of long-distance dispersal for a few of its commonest species. Two species earlier thought to belong to it but endemic to a xeric region of southeastern South America differ in having exceptionally thick upper cortices riddled with special algae-containing chambers, an apparent adaptation to their harsh habitat. They form the new genus Concamerella. Both Cetrariastrum and Concamerella have secondary-product chemistries characterized by f-orcinol depsidones and fatty acids. Excluding the fatty acids, 17 known compounds are reported from the former and seven from the latter, based upon the thin-layer chromatographic analyses of415 specimens. Three species earlier included in Everniastrum are assigned to Parmotrema or Hypotrachyna. Cetrariastrum consists of 23 species; 22 of these comprise four that are new, six that are validations of older names and 12 that are new combinations. The narrow-lobed lichens related to Parmelia cirrhata, the first of these species to have been described, are familiar to all lichenologists who have visited the New World tropics, the place of their greatest diversity. They were first recognized as a distinct assemblage by Hue (1898), who created Parmelia sect. Evernilformes for them. Hale (1976) recently placed them in a genus of their own, Everniastrum. In studying these species we find that in reality two genera differing strikingly in cortical morphology are involved, Everniastrum sensu stricto and the new ditypic genus Concamerella. The present study characterizes these genera and refines the species-level taxonomy by morphological and chemical analysis. Although the generic epithet Everniastrum has been available for only about four years, a considerable body of information has been published and stored under that name. When we found that Everniastrum is a nomen nudum, we intended to validate that name in Latin in the present study and our manuscript submitted to THE BRYOLOGIST in early February, 1981, made that provision. Almost simultaneously a regional study by Sipman (1980) ap007-2745/81/273-314