Molecular Evolution Faster in the Tropics

PRESS RELEASE – TUESDAY MAY 2 2006

Molecular Evolution Faster in the Tropics

New Zealand researchers have demonstrated for the first time that molecular evolution proceeds at a faster tempo in the tropics than in temperate zones, such as New Zealand.

This finding may explain why the tropics contain such a great richness of species.

The study appeared in the prestigious science journal Proceedings of the National Academy of Sciences USA this week entitled “The road from Santa Rosalia: a faster tempo of evolution in tropical climates”.

Shane Wright and Jeanette Keeling from the University of Auckland and Len Gillman of AUT University studied 45 woody rainforest plant Genera which has species that occur in both tropical and temperate climates.

The researchers determined rates of molecular evolution from samples in both climates by measuring the rate of nucleotide substitution in a certain region of the plants’ ribosomal DNA.

The researchers found tropical plant species had more than twice the rate of molecular evolution as closely related species in temperate regions.

Tropical samples were taken from species inhabiting New Guinea, northeast Australia, Borneo, India, Tahiti and South America. Temperate samples were taken from species inhabiting North America, southern Australia, New Zealand, Eurasia and South America.

“The biggest difference in rate of evolution we found was between New Zealand’s kauri Agathis australis and the kauri from Borneo Agathis bornensis,” say researchers Dr Wright and Dr Gillman.

Two factors that might be driving this rapid tropical molecular evolution, he says, are the smaller population sizes of some species, or warmer temperatures and higher metabolic rates.

“The former may be less likely, however, because we took care to study common species to avoid the influence of greater rates of genetic drift in small populations,” say researchers Dr Wright and Dr Gillman.

Two important implications of the study are that greater rates of molecular evolution in the tropics may provide an explanation for the grand patterns of diversity on earth, and it suggests more slowly evolving and therefore more primitive (plesiomorphic) taxa may generally occur in lower productivity regimes.

ENDS

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