Continental drift, transoceanic dispersal spread Proteaceae after Gondwanaland break-up

Continental drift and transoceanic dispersal helped spread the Proteaceae, a major group of Gondwanalands plants, to modern continents, DNA sequences and fossil records show.

Washington, Aug 9 : Continental drift and transoceanic dispersal helped spread the Proteaceae, a major group of Gondwanaland's plants, to modern continents, DNA sequences and fossil records show.

The large southern hemisphere plant family Proteaceae lived on the super-continent Gondwanaland almost 120 million years ago. As Gondwanaland broke up, it was originally thought that these plants merely moved with the newly formed continents.

But now a new study published in the Journal of Biogeography has shown that while this was the case for some of these plants, others were far too recent to have lived at the time when the super-continent broke up, and must therefore have dispersed across oceans to reach their current distribution ranges.

Nigel Barker of Rhodes University, South Africa, and his team applied a technique known as molecular dating to DNA sequences from over 40 representatives of the family from all southern continents.

Using carefully selected fossils of known age and affinity, they calculated the mutation rate of the DNA sequences. This allowed them to provide age estimates for evolutionary events in the family.

"Our results show that ancestors of some of the modern Proteaceae must have crossed the Atlantic and Indian Oceans. Thus, in Africa, for example, the spectacular genus Protea is truly Gondwanan, but 250 species from other genera that occur in the 'fynbos' vegetation (literally, 'fine leaved shrubs') of the highly diverse south-western Cape biodiversity hotspot are much younger, and have Australian relatives," said Barker.

He said the finding is important, as it has challenged the dogma that Gondwanaland's biota merely moved in situ with the continents as they broke up.

"We have to reconsider the possibility of transoceanic dispersal, as unlikely as it sounds for these plants," said Peter Weston, a researcher at the Royal Botanic Gardens, Sydney, Australia.

"While this is not the first study to invoke dispersal, it is the first on a major and diverse Gondwanan plant family with complex distribution patterns. These results are not only relevant to botanists. Ornithologists will be intrigued to find that the age of the Embothriinae, a bird-pollinated group of Proteaceae in Australia, coincides with the estimated age of the Honey-eaters, Australian nectar-feeding birds," he added.

ANI