Dactylorhiza praetermissa var. junialis - habitus in situ Trambaan, Leiden, NL 30 Jun 2010 02 Leo

On Origin, History and Infraspecific Variation;

This species was formed at least before 30,000 years ago, during the last glaciation (called the 'Weichselian' in northern Europe or the 'Würm' around the Alps), while cro-magnons were still hunting cave bears and hyenas and making sweet love to the last Neanderthals in Europe. It is an allotetraploid (4n), a hybrid which has mutated to have double the amount of chromosomes. Its original seed parent (the 'mother') was D. saccifera, a diploid (2n), the original pollen parent ('dad') was D. incarnata, also a diploid (2n). Dactylorhiza species hybridize quite often, in northwestern Europe, a swarm of similar allotetraploid species exist, all which share a similar original cross. Most of the allotetraploids are fuschii x. incarnata, or maculata x. incarnata (these are usually classed as subspecies under D. majalis); maculata is itself an old autotetraploid of fuschii. D. praetermissa is the only saccifera x. incarnata, but saccifera is itself very closely related to fuschii, a southern sister group with a more Mediterranean distribution, so the praetermissa plants are extremely similar to the majalis group.

 

But the story gets much more complicated than this due to two factors: multiple hybridization and introgression.

Many of these allotetraploids probably arose a number of times, in multiple hybridisation events, with subsequent populations perhaps later ad-mixing to varying degrees in different localities. This would mean that the varying species in the majalis complex are largely artificial; based on shared sets of particular phenotypic or ecological characteristics, but with local populations each potentially having a divergent genetic history.

For example, British praetermissa seem to share a great deal of genetics with local forms of fuschii....

Swedish

Belgian

 

But the story gets even more complicated than that. These allotetraploids also readily hybridize with each other and their original parent species; and these hybrids can back-cross or hybridize again with other members of the complex (i.e. 4n x. 2n = 3n --> 3n x. 4n --> 4n, for example), thus there is some gene-flow between species, so that particular genotypes get more represented in a particular genepool than the original hybrid would warrant. This is called 'introgression'. This gene-flow is not completely equivalent in Dactylorhiza, but is in fact often directional; 'asymmetrical'.

For example, most hybrids always have fuschii/maculata (fuschii s.l.) as seed-parent; and there seems to be is a higher proportion of of gene-flow from incarnata into fuschii s.l.

 

reticulate introgression/asymmetrical hybridization vs. multiple hybridization

Both processes bring new genetic material into the various allotetraploid lineages.

relatively common vs. quite rare.

 

The reason why I now think the variety junialis has taxonomic validity is because of the asymmetrical introgression and/or multiple hybridization events; these evolutionary processes mean that the species can better be seen as a complex of local variants, with taxonomical value (need to call 'em something) and conservation signifigance. For example, Nordic populations of allotetraploids of the majalis complex contain haplotypes derived from but no longer present in their parent populations, hence retaining genetic diversity any new polyploid hybrid could no longer regain; thus different Dutch varieties of praetermissa could indeed be significantly divergent from each other and their original parent populations. Not only that, study has also shown that in Estonia and Sweden varieties have specific ecological niches and plant associations; where varieties grow together, the ranges of micro-habitats and conditions become more narrow. This is a clear sign of ongoing speciation.

Note that another isolation mechanism producing reproductive isolation or barriers to gene-flow is divergent flowering times in the different varieties, in the Netherlands junialis flowers a week later than the nominate type.

 

millions of seeds, pre-glacial hybrid, a mistake occurred during meiosis;

 

-reticulate introgression/asymmetrical hybridization vs. multiple hybridization events?

-Seed-parent (female) was fuchsii s.l.?

-D. saccifera (2n, Medd. sister tax. to fuschii) x. incarnata (Devos et al. [2006], see also Hedrén [2001], Bateman and Denholm [2003], Devos et al. [2003], Nordström [2008])., while D. majalis = D. fuchsii s.str x. D. incarnata.

-treat all allotetraploid taxa as subspecies of D. majalis as suggested by Pedersen et al. (2003).

-has been looked at via plastids (Pillon), cpDNA, nrDNA, chloroplast (Devos) and allozyme variation (Hedrén).

 

Synonymy:

* Orchis praetermissa Druce (1914) (Basionym)

* Orchis incarnata var. integrata E.G. Camus ex Fourcy (1891)

* Orchis wirtgenii Höppner (1916)

* Orchis praetermissa var. macrantha Sipkes (1921)

! * Orchis latifolia var. junialis Verm. (1933)

! * Orchis pardalina Pugsley (1934)

* Dactylorchis praetermissa (Druce) Verm. (1947)

* Dactylorhiza wirtgenii (Höppner) Soó (1962)

* Dactylorhiza praetermissa ssp. integrata (E.G. Camus ex Fourcy) Soó (1962)

! * Dactylorhiza majalis var. junialis (Verm.) Senghas (1968)

! * Dactylorhiza praetermissa var. junialis (Verm.) Senghas (1968)

* Dactylorhiza majalis ssp. praetermissa (Druce) D.M. Moore & Soó (1978)

* Dactylorhiza incarnata ssp. praetermissa (Druce) H. Sund. (1980)

* Dactylorhiza majalis var. praetermissa (Druce) R.M. Bateman & Denholm (1983)

! * Dactylorhiza majalis var. macrantha (Sipkes) R.M. Bateman & Denholm (1983)

* Dactylorhiza integrata (E.G. Camus ex Fourcy) Aver. (1984)

! * Dactylorhiza pardalina (Pugsley) Aver. (1986)

! * Dactylorhiza praetermissa var. maculosa D. Tyteca & Gathoye (1990)

* Dactylorhiza praetermissa var. integrata (E.G. Camus ex Fourcy) D.Tyteca & Gathoye (1993)

! * Dactylorhiza praetermissa f. junialis (Verm.) P.D.Sell (1996)

Name Usage: Kew [2003], Flora Belg., Huekels [2005], PLANTS, Flora Ireland [], Tropicos, FNA, Canada

 

References:

Note these papers do not necessarily agree, and must be looked at in chronological order.

'The Evolution of Dactylorhiza (Orchidaceae) Allotetraploid Complex: Insights from nrDNA sequences and cpDNA PCR-RFLP data' by Devos et al. [2006],

'Allotetraploid Nature of Dactylorhiza praetermissa (Orchidaceae) Confirmed' by Hedrén [1996],

'Patterns of Chloroplast diversity among western European Dactylorhiza species (Orchidaceae)' by Devos et al. [2003],

'Genetic differentiation and postglacial migration of the Dactylorhiza majalis ssp. traunsteineri/lapponica complex into Fennoscandia' by Nordström & Hedrén [2008],

'Amplified fragment length polymorphisms (AFLP) reveal details of polyploid evolution in Dactylorhiza (Orchidaceae)' by Hedrén et al. [2001].

Also there are more relevant papers (and books) by Bateman, Pillon, Nordström, Hedrén, Ståhlberg, Delforge, Pridgeon, Pedersen, Tyteca and Devos

 

Done