Genetic structure and systematic relationships within the Ophrys fuciflora aggregate (Orchidaceae: Orchidinae): high diversity in Kent and a wind-induced discontinuity bisecting the Adriatic

Abstract

Background and aims: A recent phylogenetic study based on multiple datasets is used as the framework for a more detailed examination of one of the ten molecularly circumscribed groups identified, the Ophrys fuciflora aggregate. The group is highly morphologically variable, prone to phenotypic convergence, shows low levels of sequence divergence and contains an unusually large proportion of threatened taxa, including the rarest Ophrys species in the UK. The aims of this study were to (a) circumscribe minimum resolvable genetically distinct entities within the O. fuciflora aggregate, and (b) assess the likelihood of gene flow between genetically and geographically distinct entities at the species and population levels.

Methods: Fifty-five accessions sampled in Europe and Asia Minor from the O. fuciflora aggregate were studied using the AFLP genetic fingerprinting technique to evaluate levels of infraspecific and interspecific genetic variation and to assess genetic relationships between UK populations of O. fuciflora s.s. in Kent and in their continental European and Mediterranean counterparts.

Key results: The two genetically and geographically distinct groups recovered, one located in England and central Europe and one in south-eastern Europe, are incongruent with current species delimitation within the aggregate as a whole and also within O. fuciflora s.s. Genetic diversity is higher in Kent than in the rest of western and central Europe.

Conclusions: Gene flow is more likely to occur between populations in closer geographical proximity than those that are morphologically more similar. Little if any gene flow occurs between populations located in the south-eastern Mediterranean and those dispersed throughout the remainder of the distribution, revealing a genetic discontinuity that runs north-south through the Adriatic. This discontinuity is also evident in other clades of Ophrys and is tentatively attributed to the long-term influence of prevailing winds on the long-distance distribution of pollinia and especially seeds. A cline of gene flow connects populations from Kent and central and southern Europe; these individuals should therefore be considered part of an extensive meta-population. Gene flow is also evident among populations from Kent, which appear to constitute a single metapopulation. They show some evidence of hybridization, and possibly also introgression, with O. apifera.

Fig. 1.

Representative plants of the Ophrys fuciflora aggregate, reproduced at the same magnification and identified following the species classification of Delforge (2005; see Appendix). (A–C) Contrasting morphs of O. fuciflora s.s. from three different localities in Kent, UK; (D) suspected primary hybrid of O. fuciflora × apifera from Kent; (E–G) plants attributed to O. episcopalis, O. candica and supposed O. fuciflora s.s., respectively, from Crete; (H) O. oxyrrhynchos from Sicily; (I–L) plants attributed, respectively, to O. lycaena (episcopalis-like morph) and O. candica from the Peloponnese, and to O. homeri and supposed O. fuciflora s.s. from Chios. All images by R. M. Bateman.

Fig. 2.

Collection sites for the Ophrys fuciflora aggregate. Details of accessions 1–55 are given in Table 1.

Fig. 3.

Principal co-ordinates (PCoA) plot of all available AFLP data for the Ophrys fuciflora aggregate from throughout Europe. Numbers correspond to the map numbers given in Table 1. Groups from the United Kingdom (UK), south-eastern Europe (SE) and central and southern European (CSE) are displayed. The first three axes represent 18·2 %, 7·5 % and 6·0 % of the total variance, respectively.

Fig. 4.

Principal co-ordinates (PCoA) plot of AFLP data for the UK plus the central and southern European (CSE) members of the Ophrys fuciflora aggregate. Numbers correspond to the map numbers given in Table 1. The first three axes represent 16·8 %, 7·8 % and 6·5 % of the total variance, respectively.

Fig. 5.

Principal co-ordinates (PCoA) plot of AFLP data for UK Ophrys fuciflora s.s. The first three axes represent 14·0 %, 11·4 % and 9·8 % of the total variance, respectively.

Fig. 6.

Principal co-ordinates (PCoA) plot of AFLP data for southern and central European members of the O. fuciflora aggregate. Numbers correspond to the map numbers given in Table 1. The first three axes represent 17·8 %, 14·8 % and 12·7 % of the total variance, respectively.

Fig. 7.

Prevailing wind patterns in the eastern Mediterranean (after Devey, 2007, fig. 3·6). See main text for explanation of labels.