Monday, October 24, 2011

Floral gladiators evolve faster in South Africa than Rome

Gladiolus is latin for ‘little sword’, a fitting name for a plant whose flowers grow along giant spikes.  While these plants are ubiquitous in gardens across the United States, they actually are complete foreigners.  Of the 260 species around the world, almost all are from southern Africa, and none are from North or South America.

Even in the parts of the world where Gladioli are native, the distribution of their diversity varies hugely.  There are 106 species of Gladiolus in the Cape Floristic Region of South Africa and only 7 in the Mediterranean region of Europe, even though the Mediterranean region is 25 times larger than the Cape.  The two areas have similar climates and ecosystems, so what explains the 15-fold difference in diversity for these plants?

In evolutionary terms, making species is like making pancakes; to get more pancakes you either have to work longer or put more batter on the griddle and work faster.  Similarly, for there to be more Gladiolus species in southern Africa, either they have lived in southern Africa longer and have had more time for evolution to produce new species, or evolution of Gladioli proceeds faster in southern Africa than in Europe, so that new species are produced at a faster rate.

Luis Valente from the Imperial College in London and a group of international colleagues constructed a phylogenetic tree from 150 Gladiolus species from in Europe and across sub-Saharan Africa.  This ‘tree’ is like a family tree, showing how closely related all of the Gladioli are to each other.  By coloring the tips of the branches based on what region each species lives, the researchers were able to infer what region each of the ancestors used to live in, all the way back to the first Gladiolus.  From this information they could then calculate how long Gladioli have lived in different regions of Africa and Europe, as well as how quickly each of the branches of the tree found in these regions have produced new species.

So, which hypothesis explains the high Gladiolus diversity in the Cape- was it because of more time or faster evolution?  The answer, as it turns out for most questions in ecology, is both.  It is likely that the first Gladiolus species evolved in the Cape region and only much later did a Gladiolus species reach the Mediterranean and then evolve into the seven species found there.  Thus, Gladiolus in the Cape have had much more time to evolve than Gladiolus in the Mediterranean.  However, they’ve also done it faster- the rate of diversification has been 3-5 times slower in the Mediterranean than in certain parts of the Cape.

Just because Gladiolus appear to have diversified more rapidly in the Cape doesn’t mean that all plants follow this pattern.  In the group of plants called Dianthus (another flower that frequently shows up in people’s gardens), the pattern is just the opposite; Dianthus has evolved faster in the Mediterranean than in the Cape. 

You can find this article at:

ResearchBlogging.orgValente, L., Savolainen, V., Manning, J., Goldblatt, P., & Vargas, P. (2011). Explaining disparities in species richness between Mediterranean floristic regions: a case study in Gladiolus (Iridaceae) Global Ecology and Biogeography, 20 (6), 881-892 DOI: 10.1111/j.1466-8238.2010.00644.x

1 comment:

  1. Loved the pictures of the gladiolus. It's interesting to think about how these plants have evolved. Thanks for sharing.