Tropical temperatures shift plant evolution into overdrive

Auckland researchers have shown that evolution occurs twice as fast in the tropics as in areas further from the equator - which may explain why warmer places contain greater ecological diversity.

It may also explain the huge difference in evolution rates between New Zealand kauri and Borneo kauri.

The findings are published today in the US science journal Proceedings of the National Academy of Sciences.

"This is very exciting research into evolutionary trends and the implied polarity across the latitudes is of great interest," said one of the researchers, Shane Wright of Auckland University.

"The research may explain why the tropics contain such a great richness of species, and further research is required to understand what is driving the difference - smaller population sizes or warmer temperatures and higher metabolic rates," said Dr Wright, who co-authored the paper with his biological sciences colleague Jeannette Keeling, and Len Gillman from the Auckland University of Technology.

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

The biggest difference found in the rate of evolution was between New Zealand and Borneo kauri.

The researchers compared the genetic information of 45 common tropical plants with similar species in more temperate geographical areas, including 27 NZ species.

The tropical plants, from areas including Borneo, New Guinea, northeast Australia and South America, were found to have evolved much faster than those from higher latitudes such as North America, southern Australia, Eurasia and New Zealand.

To ensure the focus was on the effect of climate, the plant pairs were always from the same forest layer and were of the same shape and size. All species were from rainforests, to ensure that the temperature rather than rainfall was the variable.