Clonal diversity and geographic structure in Pleurochaete squarrosa (Pottiaceae): different sampling scale approach

Abstract

This paper describes our investigation of genetic variation and clonal structure of the Mediterranean moss Pleurochaete squarrosa (Brid.) Lindb. (Pottiaceae), using inter-simple sequence repeat (ISSR) molecular markers and trnL(UAA) (intron of plastid gene for Leu tRNA) sequence, choosing different sampling strategies and scales on 16 European populations. Moreover, the intercontinental distribution of two trnL haplotypes, previously found over a large area and including 24 populations in three continents, was also investigated. Despite the prevalent asexual reproduction, P. squarrosa shows a high level of genetic diversity. Some site features seem to affect the clonal structure at the local scale, influencing the relocation of detached fragments and the level of intermingling, but they do not substantially affect genetic diversity. The peculiar vegetative reproduction coupled with somatic mutation could partly account for the genetic variation detected. Genetic distances highlight geographic isolation and limited gene flow among populations. We found only two trnL haplotypes in Europe due to length polymorphism, but, over an intercontinental scale, only non-delete trnL was found in Africa and the USA. ISSR analysis within each population detected a higher genetic distance between the samples with different trnL haplotypes, suggesting the presence of two different genetic lineages within this species, geographically overlapping in the Mediterranean Basin.

Asexual reproduction, habitat colonization and habitat maintenance in bryophytes

“…This has been verified and proved by molecular techniques with several examples of vascular plants (Pfeiffer, 2007). It is functioning and confers comparable ecological advantages also in mosses (e.g., Abietinella abietina, Pleurochaete squarrosa, Pseudoscleropodium purum, Rhytidium rugosum; Pfeiffer et al, 2006;Grundmann et al, 2008;Spagnuolo et al, 2009;Lieske, 2010). Especially in species lacking sporophytes (unisexual ones) repeated asexual reproduction leads to widely distributed, however, genetic identical clones.…”

“…Further applied techniques are the RAPD-technique (Random Amplified Polymorphic DNA), Microsatellite-analyses, and Iso(en)zyme analyses. A detailed overview of the morphological-anatomical and molecular techniques applied to bryophytes as well as to vascular plants is given, e.g., in Pfeiffer (2007), Pfeiffer et al (2006Pfeiffer et al ( , 2008, Grundmann et al (2008), Spagnuolo et al (2009), Fritz (2010 and Lieske (2010). For specific terms used, cf.…”

“…An example for clonal reproduction via caducous leaves provides the arcrocarpous moss Pleurochaete squarrosa/Pottiaceae (Grundmann et al, 2008;Spagnuolo et al, 2009). In all these examples, clonal reproduction, respectively the genetical constitution of patches, was tested and proved with molecular techniques.…”

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“…In cladistics, paraphyly is to be methodologically avoided, but in macroevolutionary systematics it is a desideratum as it indicates direction of linear descent, progenitor to descendant. Clearly, dense sampling similar to that done by Spagnuolo et al (2009) or Shaw (2000) is needed. Given great molecular variation among strains, the finding of sufficient similarity in terms of high Bayesian support to separate two terminal strains from a third strain on a lower branch allows the hypothesis that there are indeed molecular races showing microevolutionary linear descent among the variation.…”

“…There was no macroevolutionarily informative taxon-based heterophyly. Spagnuolo et al (2009) published a study sampling molecular genetic variation in Mediterranean populations of Pleurochaete squarrosa in which considerable inter-and intra-population diversity was noted with some cladistic structure.…”