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Population Genetics of UK Orchids

Orchis militaris.

Of the approximately 50 species of orchids native to the UK, many are rare, and some of them spectacularly so.  For example, Cypripedium calceolus was reduced to a single plant, largely due to over collection in the 20th Century, and Epipogium aphyllum has not been seen in the UK since 1986.  As a result of this high level of rarity and the high profile of many orchids in documents such as Schedule 8 of the Wildlife and Countryside Act 1981 (12 species and two subspecies are listed), orchids have formed a major focus for the work of the Conservation Genetics Group (part of the Genetics Section) since its formation in the mid 1990s.

Projects are chosen in close collaboration with the statutory conservation agencies, notably English Nature, and the taxa are targeted as ones for which genetic data will have a clear application in deciding management strategies. Questions relate to variation within and between populations, confirmation of native status of cultivated plants, identification of hybrids, and others.  Current subjects for study include Cephalanthera longifolia, Cephalanthera rubra, Cypripedium calceolus, Dactylorhiza species, Ophrys fuciflora, Ophrys sphegodes, Orchis militaris, Orchis purpurea and Orchis simia.  Results from our studies are then fed back to the relevant agency/agencies in the form of conservation genetics reports, with recommendations for management changes in light of the genetic data when appropriate.  Studies are also published in peer-reviewed journals as appropriate.

The work on Ophrys is a collaborative project with the Natural History Museum, London and the University of Reading.  In addition to population genetics, it includes a phylogenetic study. However, due to the closeness of many Ophrys species, standard phylogenetic analyses based on DNA sequence data do not resolve the relationships, and we are using a fingerprinting-based approach to allow us to address this problem. 

Our studies of Orchis species have revealed that many populations thought to be genetically pure in fact show evidence of hybridisation or introgression.  This is currently the subject of a major study to assess the extent of this.

Vinogradov (2003) a strong correlation with genome size and rarity (as expressed as IUCN categories) has been demonstrated, with species with larger genomes tending to be rarer than those with small genomes.  This is reflected in the range of species worked on in this project as species of Cephalanthera, Cypripedium, Ophrys and Orchis all have large to very large genomes.  However, the large genome sizes cause problems with standard fingerprinting techniques, notably AFLP (amplified fragment length polymorphism) and nuclear microsatellites, which are often compromised or ineffective in taxa with large genomes.  We are therefore investigating the use of other markers to use with these species where appropriate.  Also, an unexpected benefit was that we have been able to expand our studies of the role of retrotransposons in species with large genomes because many of the DNA fragments selected in AFLP turn out to be parts of retrotransposons.

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