Speciation in Protea cynaroides

(1/4) > >>

Hermes (June 10, 2010, 00:55:34 AM):
Qualification: I am not a biologist. The opening section is elementary and intended for novices like myself.

1. What is speciation?

Speciation occurs when two variants of a species have diverged to the extent that they are viewed as two separate species. Unlike stellar constellations, which are defined rather randomly and merely for ease of reference, the classification of life forms (taxonomy) is done according to more scientific criteria, yet sometimes blurred.

Photo from Birds of South Africa by Dr. Austin Roberts

The thirteen birds in this picture belong to twelve different species of Francolin (patryse). The two in the bottom left corner are the male and female of the same species. Make sure that you can distinguish them – it may come up in the exam! ;)

Photo from The Greatest Show on Earth by Richard Dawkins

These two guys, the Chihuahua and Great Dane, belong to the same species.

Where’s the trick then? An important criterion (though not the only one) in taxonomy is whether they can produce descendants naturally. The Francolins in the first picture do not cross breed and reproduce naturally. Can the Chihuahua and the Great Dane? Not with all the Red Bull in the world, but they are linked by intermediaries which can mate and produce offspring. Should the intermediary dog breeds all become extinct, one would have to reconsider the classification. Note that the different species of Francolin evolved through natural selection, whereas the dogs were deliberately bred through artificial selection by humans.

South Africa’s king protea has “now” reached a stage in evolutionary divergence where we may “soon” have five different national flowers. Bear in mind that we are talking in the context of a very long timeframe.

Hermes (June 10, 2010, 01:13:16 AM):
2. The Proteaceae

Extract from South Africa’s Proteaceae by Dr. Marie Vogts:

The Proteaceae are an ancient family, probably one of the oldest groups of flowering plants. Scientific probes into the early history of plant-life have shown that the ancestors of today’s proteas were present in Gondwanaland long before it began breaking up 300 million years ago. Paleontological studies indicate that this family of the southern hemisphere was then already divided into its two sub-families: Proteoideae and Grevilleoidease. While the Proteoidease are best represented in southern Africa, the other sub-family is concentrated in Australia and South America, as well as those smaller segments of Gondwanaland which drifted as far north as eastern Asia. No genus is common to both South Africa and Australia, though South America share more than half its genera with Australia, suggesting that Africa was isolated before the links between the other parts of the super-continent were broken.

With the exception of Brabejum, the wild almond of the Cape, the African species form a closely knit whole. Madagascar, at one time almost certainly part of Africa, retains in its flora important links with the mainland. It is not surprising, therefore, that one species, a member of the genus Faurea, grows there naturally. None of the other African Proteaceae is to be found elsewhere in nature.

The 329 South African species are distributed from the south-western Cape along the southern and eastern parts of the country to the Limpopo River in the north. Of these, 92 percent, or just over 300, are restricted to the narrow mountainous coastal belt from Clanwilliam to Grahamstown. Since the Cape folded mountain region is the home of the majority of proteas, it is feasible that the extraordinary diversity of species, as well as their richness and variation, is primarily attributable to the highly dissected topography of the area. For here, where one population may be completely isolated from its neighbour, it has had the chance to develop undisturbed and react independently to the climatic changes of the past.
Hermes (June 10, 2010, 01:19:36 AM):
3. Protea cynaroides

Extract from South Africa’s Proteaceae by Dr. Marie Vogts:

The king protea, one of the most widespread of the Cape proteas, occurs in many places throughout the south-western and southern parts of the country, from the Cedarberg to Beggar’s Bush, a few kilometres east of Grahamstown. It is not found, however, on the Swartberg ranges. P. cynaroides always grows in acid, sandy soil derived from Table Mountain Sandstone or Witteberg quartzite. The specific name, meaning ‘like cynara’ – a globe artichoke – hardly captures the magnificence of these beautiful flowers, but was an obvious association for Linnaeus to use when naming the specimen sent to him. Reuse protea, the Afrikaans vernacular name, is self-evident, but water protea, the term used in the northern parts of the western Cape, is less so. Nonetheless, it is appropriate, as although P. cynaroides thrives in well-drained sites, it is a water-loving species and throughout the Koue Bokkeveld and Cedarberg, an area prone to long periods without rain, it favours the banks of streams. Here it enjoys the best of both worlds – sufficient moisture in time of drought and a quickly draining site during rains.

[The name protea originates from a character in Greek mythology, Proteus, who could supposedly change its shape at will. Likewise protea species are widely diverse.]

The shrub, 0,3 – 2m in height, has a persistent rootstock from which new shoots will sprout after the aerial parts have been burnt off or cut down. With its distinctive leaves and huge flower-heads, up to 300mm in diameter, P. cynaroides is the most outstanding species in the genus – and yet also the most variable. Numerous local races occur, but all are united by a single common factor: their leaves are glabrous [free from hair or down] and have very prominent leafstalks. Variation is part of nature, but in the context of this species, it takes on a special significance as the dissimilarities exhibited by the various populations have evolved in isolated locations. Thus P. cynaroides provides a living and fascinating example of a plant on the evolutionary threshold of splitting into further species.
Hermes (June 10, 2010, 01:27:18 AM):
4. Variation in Protea cynaroides

Extract from South Africa’s Proteaceae by Dr. Marie Vogts:

Colour and form variations of Protea cynaroides. The photograph was taken in October, therefore the summer an autumn flowerers of the western Cape are not included. a A bronze ecotype with spiky bracts from the Langeberg foothills near Riversdale. b & c A deep rose, small narrow-leaved variant from the Garden Route coastal region. d & e A light pink, long-leaved form from the eastern Cape. f, g & h A rich pink, large bowl-shaped form from three localities on the higher slopes of the Outeniqua mountains. i The bright red form of a small narrow-leaved variant from the Knysna coastal region.

Variants of the species not only differ in the colour and form of their flower-heads and foliage, but also in flowering-times. Because these characteristics and qualities are stable, they are exploited to great advantage and the grower can develop further the best variant for his needs.
Hermes (June 10, 2010, 01:38:13 AM):
5. How is this speciation?

There are a number of indications that we are looking at speciation in progress:

· The variants developed naturally;
· They developed in geographically isolated habitats;
· Even when imported into one another’s habitats, their form remains stable;
· Even when imported into one another’s habitats, their various flowering seasons remain stable.

Natural hybridisation is not entirely excluded and it would be too early to talk of distinct species yet. We can expect natural selection to continue favouring the variants that are specifically adapted to each habitat, acting to the detriment of intermediaries and hybrids.

The Greatest Show on Earth by Richard Dawkins is published by Bantam Press.
South Africa’s Proteaceae by Marie Vogts is published by Struik


[0] Message Index

[#] Next page

Skeptic Forum Board Index

Non-mobile version of page