BATEMAN, RICHARD M.1*, PETER M. HOLLINGSWORTH2, JANE SQUIRRELL2, JAMES H. DICKSON3, and MARK TEBBITT4. 1Department of Botany, Natural History Museum, Cromwell Road, London SW7 5BD, UK; 2Royal Botanic Garden, Inverleith Row, Edinburgh, EH3 5LR, UK; 3DEEB, Glasgow University, Glasgow, G12 8QQ, UK; 4Brooklyn Botanic Garden, 1000 Washington Avenue, Brooklyn, NY 11225-1099, USA. - Population genetic structure, phylogeny, and breeding system in Epipactis (Orchidaceae: Neottieae).
Deviations from random mating are an important determinant of plant
species evolution. Taxonomic complexity and controversy, and the
resulting difficulties in assessing conservation priorities, are often
associated with 'critical groups' incongruent with the classic Hardy-Weinberg
equilibrium mode of population genetic structure. In critical genera such as
Epipactis breeding system transitions are hypothesized to be an important
mechanism underpinning speciation. We have erected a multi-gene molecular
phylogenetic framework for the Neottieae before using molecular markers to
investigate the amounts and partitioning of genetic variability in 26 putative
species of Epipactis. These species have contrasting floral morphologies,
geographical distributions, habitat preferences, and propensities for vegetative
spread. All species with floral morphologies consistent with self-pollination were
homozygous and uniform at all examined allozyme loci. In contrast, species whose
floral morphologies were consistent with allogamy differed considerably in degrees of
genetic variability, with this variability typically organized according to
Hardy-Weinberg expectations. Thus, the transition to autogamy has an overriding
effect on the organisation of intra-specific genetic variation, but other factors
determine the comparative amounts of genetic variation in allogamous species. Using a
combination of isozymes, inter-SSRs, cpDNA RFLPs, and cpDNA SSRs, we determined
whether autogamous taxa represent distinct lineages rather than minor mutational
variants. All of the markers we employed suggest that the transition from allogamy to
autogamy is highly iterative, generating multiple homozygous and uniform lineages,
each distinct and separable by fixed allelic differences from other comparable
lineages.
Key words: breeding system, conservation genetics, Epipactis, molecular markers, Orchidaceae, speciation