It is well studied that Cephalanthera damasonium belongs to those orchids which can live without chlorophyllum – together with other species of the tribe of Neottieae or the genus Epipactis. While exploring a mixed forest near Lahnstein (Rhineland-Palatinate) together with Ingo Beller of the Arbeitskreis Heimische Orchideen (AHO) Rheinland-Pfalz, we found a group of three albino plants in addition to three green-leafed Cephalanthera damasonium. Of the apochromic plants one has two flowers, one only one flower and one has no flower. Those albino plants receive their organic carbon with the help of fungi. A study of V. Tranchida-Lombardo, M. Roy, E. Bugot, G. Santoro, Ü.Püttsepp, M. Selosse and S. Cozzolino, published in 2010 in Plant Biology suggests that the albino Cephalanthera damasonium may be viewed as “an intermediate step in the evolutionary emergence of mycoheterotrophy”, or of the ability to be nourished both by fungi and photosynthesis. By means of genetic analyses the authors declare: “Albinos could be either permanent mutants, as suggested by phenotype stability over the years, or transitory phenotypic stages, in which genes involved in the photosynthetic pathway can switch off depending on micro-environmental conditions (e.g., the amount of C resources provided by the nearby fungal mycelia or tree roots) that prevent greening.”
Tag-Archive for » Evolution «
Still looking for any hints to shed some light on the albiflora phenomenon, I visited Richard Bateman in London. The white-flowered morphs “are of greatest interest to me because of their relative frequencies in the diploid and the tetraploid groups of Dactylorhiza”, he told me. “If your mind works its ways through the different diploids – incarnata, fuchsii, sambucina – they all show colour polymorphism. And they all have a certain number of very pale or white individuals.” Quite different are the observations with tetraploid Dactylorhiza species like praetermissa, majalis or alpestris. Bateman noted: “I’ve only found one albino praetermissa and one albino traunsteinerioides in 30 years of going in the field.” Quite younger is the albiflora.eu project – but up to now only some scattered findings of white-flowered Dactylorhiza majalis have been reported – and none of praetermissa or traunsteineri. As a possible explanation Bateman noted: “Presumably, in the tetraploids there has to be a minimum of four copies of a gene that is malfunctioning to cause the albinism. So I think the tetraploids are buffered against albinism by having additional copies of the genes that generate the anthocyanin pigments.”
Arguing with him about the negative connotations of the term malfunction, Bateman answered: “Most organisms are ‘designed’ to remain the way they are and not to change [substantially]. So, from a genetic viewpoint, any change that is expressed is a malfunction. I agree the malfunction could be beneficial rather than negative but most times it’s negative.”
Bateman’s main interests in research are the questions of speciation or at least the question of what might lead to evolutionary divergence between populations: “The genus level – for me at least – is solved. The species level interests me the most now. That’s were the most challenging topics still have to be addressed – how orchids speciate.” Despite a huge literature on the topic, Bateman noted, those questions are still not adequately solved. “Each time I address a particular set of orchids, the answer [to this question] is different.” So up to now, no generalization is possible. But, Bateman said, “I strongly believe that the importance of pollinator [specificity] is being exaggerated by a lot of workers.”
At least one general observation can be stated according to Bateman: “New [evolutionary] strategies are tried out constantly – more than most people believe – but I think they succeed less often than most people believe.”
In addition to such reflections on stability and change in the genetics of orchids, we wondered why hypochrome forms of Ophrys are rather green than white – obviously the Ophrys flowers still contain chlorophyll even if they lack the anthocyanins – and with good reason: “The rosette leaves of Ophrys (and Himantoglossum as well) tend to be dead before the flowers properly open”, Bateman said. “So I don’t think there is much supply of nutrient coming from [root to flower]. The flower has become autonomous … whereas in Orchis or Anacamptis the flowers are far less independent.” So, Ophrys flowers are quite special. “One of the most striking things when you start working on the flowers, cutting them up looking at them under microscope, you realize how much energy is invested in an Ophrys flower. There is a lot of tissue.”
After the visit, the Royal Botanical Gardens in Kew have been the very right place to further contemplate on the miracles of nature. (With thanks to Richard Bateman for reviewing his quotes, additional notes are marked with brackets)
In an essay about the taxonomic mess with European orchids, Richard Bateman stresses the importance to develop clear criteria for classification instead of individualistic conclusions. The article titled “Evolutionary classification of maximising explicit evidence and minimising authoritarian speculation” (In: Journal Europäischer Orchideen, Vol. 41/2, July 2009) explains how a monophyletic classification (i.e. a classification with a group of organisms forming a clade with a common ancestor and comprising all the descendants of this ancestor) can be derived from the phylogeny (evolution) of species.
Bateman recognises the value of morphological characteristics, but stresses that molecular data should be the main source for a scientific taxonomy. He criticizes that other classifications are often only “the result of personal opinion” and says: “21st Century data are being constrained by voluntarily retaining an 18th Century approach to biological classification”. Regarding taxonomic debates about the genera Dactylorhiza/Coeloglossum, Neottia/Listera or Gymnadenia/Nigritella he complains: “Authors decide which names they will accept and which they will reject from the many classifications already available, as though they were selecting products from the supermarket shelves.”
Arguing for clear rules founded on molecular research, Bateman also mentions the “origination of white-flowered individuals in many orchid lineages” as a result of a convergent evolution – this term describes the development of similar features with species who have no genetic relationship, often initiated by functional or environmental adaptation. But is there really such an adaptation when orchids develop white flowers, “achieved by suppressing any one stage in the biosynthetic pathway that generates anthocyanin pigments”? And what would be the object of such an adaptation?
Today, 200 years ago, Charles Darwin was born – his vivid interest in varieties of animals and plants has led him to the insights of evolution: Species are not created once and forever but are rather the result of a process, which is partly still continuing. Especially the relatively young family of orchids is still in the midst of its development, and nature is trying to go new ways. One of them are colour variations like white orchids.
In his book about “The various contrivances by which orchids are fertilised by insects” (1862, 2. Auflage 1877), Darwin studied the structure of orchid flowers in relation to their pollinators. About Platanthera chlorantha (which he called Habenaria chlorantha) he wrote, that they are pollinated by moths – due to their long spur filled with nectar and an intense scent at night: “The remarkable length of the nectary, containing much nectar, the white colour of the conspicuous flower, and the strong sweet odour emitted at night, all show that this plant depends for it fertilisation on the larger nocturnal Lepidoptera.”(p.85). In a famous forecast Darwin estimated that there must be a pollinator in Madagascar matching the orchid Angraecum sesquipedale which has a spur with a length of 25 cm: “In Madagascar there must be moths with probosces capable of extension to a length of between ten and eleven inches!” (p. 198). In 1903, 41 years later, the appropriate butterfly was found, Xanthopan morgani.