The mechanics of snapdragon survival has shed new light on the process of evolution, explains Roger Highfield
The positive effects are caused by polysaccharides, the antiviral and antimicrobial compounds you could try here order viagra online of Inyokaku.More researches are needed to discover all of the secrets of epimedium plant. When the man loses all his calm and peace and when his love life is on stake then the best order generic cialis solution in such a situation is to switch over to the Internet for prescriptions. Vitamin C is known for its importance in overall health, but it is specifically good for the penis. viagra cialis for sale So, online pharmacies are able to buy generic viagra provide you the most performing medicine of generic kind.
While they were exploring the foothills at the border between south-west France and Spain, Enrico Coen and his friend Christophe Thébaud stumbled across a pretty problem, one that has created a mountain for evolutionary scientists to climb.
While driving in a valley, they passed an abundance of snapdragons, all coloured magenta. But near the town of Ripoll they spotted something fascinating, a natural floral boundary. In a hybrid zone hundreds of metres across, orange and whitish snapdragons thrived. Beyond them stretched acres of snapdragons of another colour, all yellow.
European snapdragons can be crossed to make hybrids and, as anyone who mixes paints will tell you, yellow plus pink is orange. Were the scientists witnessing the recent birth of a new, orange species, a blend of the genetic palette to create another member of the 28 or so Antirrhinum species that can be found in southern Europe? Or were the orange snapdragons the equivalent of mules, sterile crosses that could be born but not thrive?
This is just the kind of simple question that leads to new scientific insights. Prof Coen, Annabel Whibley and Nicolas Langlade at the John Innes Centre near Norwich and Prof Andrew Bangham and Andy Hannah of the University of East Anglia decided to study the snapdragon problem in collaboration with Dr Thébaud of the Université Paul Sabatier, Toulouse.
In the journal Science, they provided the answer with an explanation that ranges far beyond the world of florists and botanists. The work sheds new light on the mechanics of evolution and undermines an argument often used by Creationists. But there is bad news for evolutionary scientists, too. Their favourite metaphor for describing evolution is primitive and misleading.
The team found something remarkable around the floral boundary: there was plenty of mixing between genes of the yellow and magenta plants but much less mixing when it comes to the genes controlling pigment colours. The scientists concluded that the orange-flowered snapdragon was not a new species in the making but the equivalent of a mule, the dead-end cross of a donkey and a horse.
What was it about this particular colour? Orange varieties of flowers do, of course, exist: plant breeders have selected them. But it turns out that although an orange snapdragon can make seed, this colour is not very visible to bees, the insects which pollinate the plants and enable them to reproduce. This is not a problem for other orange flowers which appear bright at ultraviolet frequencies (which bees are sensitive to, unlike us), as is the case with poppies; or which are pollinated by humming birds (which can see orange.) But this is a problem for the snapdragons, which depend on bees.
Scientists have a powerful visual metaphor they use to express the problem facing orange blooms. They draw an abstract landscape, using a method that was unveiled in 1932 by an American geneticist, Sewall Wright. In his mind’s eye he saw mathematical panoramas which reveal how thousands of genes in the genetic recipe of a plant or animal influence its success, an “adaptive landscape” of genetic possibilities.
One of the landscape’s three dimensions could represent how much a snapdragon plant uses the magenta gene. The second could be the yellow gene. And the third, the vertical dimension, could represent how well plants with each combination of colours reproduce. That would mean pure magenta or yellow would produce towering mountains of success (or fitness, as scientists like to say), while blends that are doomed by lack of bee interest (orange) create troughs.
But this simple answer leads to another question. For a snapdragon to evolve between sporting the magenta flowers of Antirrhinum majus pseudomajus and the yellow ones of Antirrhinium majus striatum, as it undoubtedly did in the past, it would first have to produce less-attractive orange flowers.
That would mean the path of evolution taking the low road, through an unfit intermediate that bees would often ignore. That would go against the idea of the survival of the fittest, which says that only the plants with the most attractive flowers are able to compete thrive. And that, in turn, would be great news for Creationists. If Darwin’s theory of natural selection fails because critical intermediates – such as these elusive orange snapdragons – perform no function for selection to preserve then God Himself would have to intervene to help yellow become magenta and vice versa.
But in the case of snapdragons, colour is controlled by at least three genes: Rosea and Eluta, which affect the magenta pigment anthocyanin, and Sulfurea, which affects the yellow pigment, aurone. That means we need four dimensions (one for each gene and one for how well the various gene combinations reproduce), when Wright’s metaphor is usually kept to three because that is all the human brain can easily cope with.
Today, there is a way to explore more dimensions. “There are computational methods for understanding and visualising high-dimensional problem,” said Prof Bangham. Visualised in higher dimensions, a clear high road from magenta to yellow opens up, via paler varieties, without having to evolve through the lower orange forms that bees are less interested in, and without invoking the help of God.
“This is a totally different way of picturing evolution. The evolutionary possibilities are enormous and much richer than traditionally depicted,” said Prof Coen. “We now understand how these plants can evolve to produce different colours whilst staying attractive to pollinating insects – we’ve found that colour is variable but constrained to a defined path.” Beyond the snapdragon, this kind of study will also help understand how the process of evolution creates new species.
The message complements insights into evolution that have come from closer to home, on the St Kilda archipelago, the most remote part of the British Isles. There a team led by Dr Josephine Pemberton is counting, measuring and DNA fingerprinting its brown, white and black residents, the primitive Soay sheep.
The goat-like stocky animals are the descendants of a Bronze Age breed that has been resident on St Kilda for some 4,000 years. St Kilda was abandoned by the 36 remaining human residents in 1930, but not by the sheep. Research on them began in 1959 and now amounts to one of the most detailed population studies in the world, providing profound insights into evolution.
There are many examples of how, when isolated on islands, species shrink. And indeed the Soay sheep, which currently number about 1,800, are becoming smaller. The usual theoretical explanation is that islands have limited resources, so for the numbers of sheep to grow, the animals shrink.
But it is the bigger, fast growing, sheep that tend to survive St Kilda’s bleak winters, which can see the population crash by up to 60 per cent (there are no natural predators.) “We know bigger sheep do better,” said Dr Alastair Wilson, one of the team. “Evolution predicts they should be getting larger, yet they are not.”
The effects of growth boosting genes are being masked in some way, perhaps because the sheep are changing their environment and food supply. But if that explains what is happening to the sheep, what about local mice? They are getting bigger, now half way towards being rat sized.
This does not mean Darwin got it wrong. What it does suggest is that Darwin’s theory will only realise its full potential when translated from simple stories, metaphors and pictures into a mathematical form that can capture all the nuances, richness and complexity of the real world.