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Genetic Variation Within and Among Populations of the Threatened Lichen Lobaria Pulmonaria in Switzerland and Implications for I

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Genetic Variation Within and Among Populations of the Threatened Lichen Lobaria Pulmonaria in Switzerland and Implications for I MEC820.fm Page 2049 Saturday, December 18, 1999 1:20 PM Molecular Ecology (1999) 8, 2049–2059 GeneticBlackwell Science, Ltd variation within and among populations of the threatened lichen Lobaria pulmonaria in Switzerland and implications for its conservation S. ZOLLER,* F. LUTZONI† and C. SCHEIDEGGER* *Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf, Switzerland, †Department of Botany, The Field Museum of Natural History, Chicago IL 60605, USA Abstract The foliose epiphytic lichen Lobaria pulmonaria has suffered a significant decline in European lowlands during the last decades and therefore is considered as endangered throughout Europe. An assessment of the genetic variability is necessary to formulate biologically sound conservation recommendations for this species. We investigated the genetic diversity of the fungal symbiont of L. pulmonaria using 143 specimens sampled from six populations (two small, one medium, three large) in the lowland, the Jura Moun- tains, the pre-Alps and the Alps of Switzerland. Among all nuclear and mitochondrial regions sequenced for this study, variability was found only in the internal transcribed spacer (ITS I), with three polymorphic sites, and in the nuclear ribosomal large subunit (nrLSU), with four polymorphic sites. The variable sites in the nrLSU are all located within a putative spliceosomal intron. We sequenced these two regions for 81 specimens and detected six genotypes. Two genotypes were common, two were found only in the more diverse populations and two were found only in one population each. There was no correlation between population size and genetic diversity. The highest genetic diversity was found in populations where the fungal symbiont is reproducing sexually. Popula- tions with low genetic diversity included only the two same common genotypes. Our study provides evidence suggesting that L. pulmonaria is self-incompatible and hetero- thallic. Based on our results we give populations with sexually reproducing individuals a higher rank in terms of conservation priority than strictly asexual populations. The remaining lowland populations are so small, that one single catastrophic event such as a windthrow might destroy the entire population. Hence we suggest augmenting such populations in size and genetic diversity using small thallus fragments or vegetat- ive diaspores collected in other populations. As we did not detect any locally adapted genotypes, these transplants can be taken from any other genetically diverse population in Switzerland. Keywords: conservation, genetic variation, lichens, nuclear and mitochondrial DNA sequences, sexual reproduction Received 24 April 1999; revision received 21 August 1999; accepted 21 August 1999 Introduction (Daniels et al. 1996; James & Ashburner 1997). This procedure is recognized as an important conservation measure by The assessment of genetic variation and its conservation many authors (Falk & Holsinger 1991; Loeschcke et al. is widely used in preserving threatened organisms par- 1994; Petit et al. 1998) although some of the existing ticularly in species with small and isolated populations empirical data are conflicting (see Ellstrand & Elam 1993). Correspondence: C. Scheidegger. Fax: + 41-1739-22-15; E-mail: In general, a higher genetic variation is assumed to improve [email protected] the fitness of a species and enhance the probability of © 1999 Blackwell Science Ltd MEC820.fm Page 2050 Saturday, December 18, 1999 1:20 PM 2050 S. ZOLLER, F. LUTZONI and C. SCHEIDEGGER population survival (Mitton & Grant 1984; Wildt et al. chlorophaea complex, which probably includes several taxa, 1987; Hedrick & Miller 1992). 13 genotypes were found within one mat (DePriest 1994). The epiphytic lichen Lobaria pulmonaria (L.) Hoffm. is On the other hand, in Cladina subtenuis no variation in distributed over parts of Europe, Asia, North America the nrSSU was found within populations but some was and Africa (Yoshimura 1971). In Switzerland it grows detected among populations (Beard & DePriest 1996). mainly on deciduous trees such as beech (Fagus sylvatica) In our study we investigated the genetic diversity and sycamore maple (Acer pseudoplatanus). Vegetative of the fungal symbiont of L. pulmonaria in 81 samples diaspores (isidioid soredia) include both symbionts and from six populations in the lowland, the Jura mountains, are formed on the upper cortex of the thallus. Occasion- the northern pre-Alps and the Alps in Switzerland. We ally, apothecia, the fruiting bodies of the fungal symbiont present, for the first time, an extensive study on the (producing ascospores), are formed along the ridges and genetic variation of a lichen species using DNA sequences. margins of the thallus. The photobiont is a green algae We investigated several mitochondrial and nuclear genes and rarely a third symbiont, a cyanobacteria is found for variability using PCR and automated sequencing. in cephallodia on the upper cortex. The thallus is loosely We examined the influence of population size, history, attached on the substratum and spreads widely, often isolation and the mode of reproduction (sexual or asexual) exceeding 20 cm in diameter. This species, similar to many on the genetic variability of the populations. These other lichens, is sensitive to acidic air pollution (Sigal results provide information essential for biologically & Johnston 1986) and ozone (Scheidegger & Schroeter sound recommendations for appropriate conservation 1995). Growth experiments using soredia, thallus fragments measures and management priorities. (Scheidegger 1995; Scheidegger et al. 1995) and ascospores (B. Frey, personal communication) show that L. pulmonaria Materials and methods is a species with generation cycles of up to 25 years. Furthermore, Scheidegger (1995) has shown that L. Lichen material and preparation pulmonaria is limited in its capability to establish new thalli on neighbouring trees. A total of 143 Lobaria pulmonaria thallus fragments were The foliose lichen L. pulmonaria has suffered a con- collected from six locations in Switzerland north of the siderable decline in central and northern Europe since the Alps (Fig. 1). In the two small (less than 50 thalli) and last century (Hallingbäck & Martinsson 1987) and is isolated lowland populations of Vordemwald (coordinates considered to be critically endangered particularly in the 634.0/237.4) and Forst Bern (coordinates 589.1/196.7), we lowland regions (Türk & Wittmann 1986; Clerc et al. 1992; collected 25 fragments out of approximately 40 known thalli Wirth et al. 1996). The sharp decline in number and size of and six fragments out of six known thalli, respectively. In populations in lower elevations of Switzerland is most the two large populations of Muotatal (coordinates 705.8/ probably due to habitat destruction, changes in forest 204.5) and Lauenen (coordinates 591.9/137.8) in the eastern management (such as extensive plantation of conifers) and western Alps, 30 fragments out of 600 known thalli and air pollution, coupled with poor dispersal mechan- and 32 fragments out of 400 known thalli were collected, isms and long generation time of this species. The respectively. In Marchairuz (coordinates 509.0/156.2), a remaining small lowland populations consist of only a large population in the Jura mountains of 600 known thalli, few thalli and are widely separated from each other and and in Toggenburg (coordinates 737.5/227.2), a medium from the larger populations in the Alps and the Jura population in the eastern pre-Alps of around 150 known mountains. Only two lowland populations are known to thalli, 35 and 15 fragments were collected, respectively. have more than five thalli. Such small populations are The fragments were about 5–10 cm2 in size. In general presumed to be more sensitive to stochastic environ- we collected one sample per tree, but for two trees in mental changes (Shaffer 1981; Lande 1988) and more Vordemwald four thalli were sampled per tree. Trees were vulnerable to extinction due to loss of genetic variation chosen in order to cover the total distribution of the popula- (Huenneke 1991; Lynch et al. 1995). tion. No preferences were made concerning tree species, Studies of variation within lichen species have been size or exposure. To avoid any damage to populations, conducted using enzyme polymorphism (Fahselt 1986; the thallus size had to be larger than at least twice the Hageman & Fahselt 1990; Nevo et al. 1997) and restriction- size of the collected fragment. To get haploid fungal site patterns of the nuclear ribosomal small subunit RNA material only, fragments were taken from vegetative parts gene (nrSSU) resulting from the presence/absence of of the thallus where no apothecia were visible. Fragments group-I introns in the fungal component of the lichen were stored air dried and prepared within a few days in genus Cladonia (DePriest & Been 1992; DePriest 1993; the laboratory. For each thallus that was sampled we Beard & DePriest 1996). In these studies, considerable documented the presence or absence of apothecia and the within-population variation was detected. In the Cladonia type of vegetative diaspore (soredia, isidioid soredia). © 1999 Blackwell Science Ltd, Molecular Ecology, 8, 2049–2059 MEC820.fm Page 2051 Saturday, December 18, 1999 1:20 PM GENETIC VARIATION OF LOBARIA PULMONARIA 2051 Fig. 1 Geographic location and genotype frequencies of the six populations investigated. Six genotypes were found: AA, AB, AC, CA, CB and DA. The five regions on
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