Orchids “adapt” to colour preferences of pollinators

This hypothesis has been formulated by Hannes Paulus in a contribution for the latest edition of the Journal Europäischer Orchideen (Hannes F. Paulus: Zur Bestäubungsbiologie der Gattung Ophrys in Nordspanien: Freilandstudien an Ophrys aveyronensis, O. subinsectifera, O. riojana, O. vasconica und O. forestieri. J. Eur. Orchideen. 49 (3-4): 427-471).

In this article the author studies both populations of Ophrys aveyronensis in Southern France and Northern Spain – the last one termed as Ophrys aveyronensis subsp. vitorica. According to Paulus it is just one species, because both are pollinated by the bee Andrena hattorfiana.

Paulus points to the fact that this bee is specialised on the widow-flower (Knautia). The pink inflorescence of this plant has the same colour as the perigone, i.e. the sepals and petals, of Ophrys aveyronensis. The expert of Ophrys is stating: It can be expected that this is not just a mere chance but an adaptation to the main nourishing plant of the pollinator. Knautia shows at the same time more deeply pink flowers as flowers tending to white.

This evidence is confirming the approach to also look for other plants when we search for reasons why albiflora forms of different orchid species are more often in certain places.

The dynamics of evolution on the Dactylorhiza meadow

Dactylorhiza fuchsii f. albiflora

Seven years after my first observations on a meadow in the valley of the small river Bieber in the northern region of the Spessart mountains I visit this special habitat again. The meadow with a wet trench in the middle is in full flowering. My estimation is that about 600 Dactylorhiza plants are flowering here: About 500 Dactylorhiza fuchsii, 50 already withered Dactylorhiza majalis and 50 hybrids Dactylorhiza fuchsii x majalis. Among the accompanying plants are Rhinanthus spec., Pedicularis palustris, Campanula patula and even a group of Arnica montana. Platanthera bifolia is just showing the first flowers.

Among the 500 Dactylorhiza fuchsii are about 400 plants with very bright flowers and a pattern of bright violet loops on the labellum. Furthermore, I count 22 albiflora forms with white flowers and non-spotted leafs. This is a rate of 4.4 per cent – much higher than you could expect if those were just spontaneous mutations. When I first visited this place on 20.6.2010 and 1.6.2012, there were less albiflora plants. Only about 80 of the 500 Dactylorhiza fuchsii have an intense violet colour. This meadow presumably has its own dynamics of evolution, developing increasingly bright forms of Dactylorhiza fuchsii.

Dactylorhiza fuchsii f. albiflora

Dactylorhiza fuchsii f. albiflora

There might be a relation with the learning experience of bees: With the earlier flowering Dactylorhiza majalis, many pollinators may have already made the experience that there is no nectar in the spur of violet orchid flowers. While developing brighter flowers, Dactylorhiza fuchsii might counteract this learning experience. Young honey bees still have to make this experience like this one on the flowers of the hybrid Dactylorhiza fuchsii x majalis: