Population genetics on anthropogenic and natural sites, subspecies differentiation and fungal community of Gymnadenia conopsea s.l. (Orchidaceae)

Today human impact is the main driver of global environmental change. One of the most severe anthropogenic changes is land transformation, which has altered 40- 50% of Earth’s surface into urban and agricultural systems. Orchids are particularly vulnerable to environmental changes, because with germ...

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Main Author: Stark, Christiane
Contributors: Ziegenhagen, Birgit (Prof. Dr. ) (advisor)
Format: Dissertation
Language: English
Published: Philipps-Universität Marburg 2010
Edition: http://dx.doi.org/10.17192/z2011.0106
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Summary: Today human impact is the main driver of global environmental change. One of the most severe anthropogenic changes is land transformation, which has altered 40- 50% of Earth’s surface into urban and agricultural systems. Orchids are particularly vulnerable to environmental changes, because with germination and pollination two important life cycle stages directly depend on symbiotic interactions. Therefore a thorough understanding of orchid biology and the factors that determine habitat suitability and orchid distribution is essential for an effective conservation of orchid diversity. Using Gymnadenia conopsea s.l. as study system, a common orchid that occurs over a wide ecological amplitude, this thesis addresses aspects of orchid biology that might be critical for orchid recruitment and the long-term persistence of populations in the wild, namely the specificity of the mycorrhizal symbiosis, population genetic diversity and genetic differentiation. The availability of suitable fungal partners is a precondition for orchid germination in the wild as they provide carbohydrates for initial growth. In one study the fungal communities of six G. conopsea s.str. populations in two study regions in East and North Germany were analysed. The 28 identified taxa revealed a high diversity of fungi associated with G. conopsea. This high diversity of associated fungi indicates that this orchid shows only little specificity to certain fungal clades, which is likely to contribute to its ability to grow in very different habitat types with the respective fungal communities. However, the taxon composition showed a clear spatial structure and only little overlap between regions, suggesting that factors at the local scale may strongly affect local species composition and hence diversity at the regional level. In all populations taxa of the known OM genera Tulasnella, Ceratobasidium, Thanatephorus and Sebacina were detected, suggesting that G. conopsea utilizes typical OM fungi as mycorrhizas. However, also ascomycetous taxa from the Pezizales and Helotiales were identified. Their continuous detection indicates that this orchid is also able to utilize ascomycetous ectomycorrhizal taxa, which could be another aspect contributing to its ability to grow in a variety of different habitats. Many orchids are well known as primary colonisers and are often found in anthropogenic habitats. In order to assess whether founder effects during colonization threaten the long-term survival of recently established populations, another study compared the genetic diversity and fitness of populations from anthropogenically disturbed and surrounding natural habitats in two German regions (East Germany: lignite post-mining area; North Germany: quarries). The results revealed a reduced genetic diversity and lowered fruit set for the populations in the lignite post-mining area, whereas no such effects were found for the quarry populations. However, the general plant performance was similar for all investigated populations. This indicates that during the colonization of post-mining areas that are often distant from potential source populations, founder effects may occur. In contrast, this problem seems negligible for G. conopsea populations in the quarries, which were spatially intermixed with source populations. Gymnadenia conopsea (L.) R.BR. s.l. is a controversial taxon. The two most commonly distinguished taxa are G. conopsea (L.) R.BR. ssp. conopsea and G. conopsea ssp. densiflora (WAHLENB.) K. RICHT., for which also a species status has been suggested. Due to a high morphological overlap between the taxa, identification in the field is difficult. Hence, for taxon assignment all investigated populations were genetically and morphologically analyzed. The analysis of the ITS region revealed a 2% nucleotide divergence, similar to the divergence between other Gymnadenia species. This, together with largely non-overlapping sets of microsatellite alleles supports the view that Gymnadenia conopsea (L.) R.BR. s.str. and Gymnadenia densiflora (WAHLENB.) DIETRICH deserve species status. G. conopsea s.str. and G. densiflora are not even sister species as the sequences of G. densiflora form a well supported monophyletic group, sharing a most recent common ancestor with G. nigra and G. austriaca. G. conopsea s.str. was either diploid or tetraploid, while G. densiflora was diploid throughout. As the microsatellite patterns of the two ploidy levels of G. conopsea s.str. were hardly differentiated and the most frequent ITS haplotypes occurred in both of them, an autopolyploid origin of tetraploid from diploid G. conopsea s.str. is likely. However, morphological differentiation was less clear. Although some traits (e.g. flower number and density) allow a fairly good distinction, due to a considerable variation an unequivocal identification will remain difficult.
DOI: http://dx.doi.org/10.17192/z2011.0106