Evolution is twice as fast in the tropics

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Evolution is twice as fast in the tropics
mongabay.com
May 1, 2006

Tropical species evolve twice as fast as temperate species according to research published in Tuesday's Proceedings of the National Academy of Sciences (PNAS).

The study, which compared the genetics of 45 common tropical plants with similar species from cooler geographical areas, suggests that evolution takes place at a faster rate in warmer climates either due to higher rates of metabolism, which leads to more genetic mutation, or shorter generations, so genetic changes are rapidly passed on to offspring.

"This is very exciting research into evolutionary trends and the implied polarity across the latitudes is of great interest," said lead author Shane Wright, a plant geneticist at the University of Auckland in New Zealand. "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."

Warmer temperatures could speed evolution by increasing rates at which chemical reactions -- including metabolism and DNA replication -- occur resulting in genetic mutations that, through the process of natural selection, can result in new species.

Monkey frog in Peru
[Photo by R. Butler]

The United States has 81 species of frogs, while Madagascar, smaller than Texas, may have some 300 (99% of which are found nowhere else). 80 frog species have been collected in a single day at localities in Peru.

Rhetus periander butterfly in Peru
[Photo by R. Butler]

Whereas all of Europe has some 321 butterfly species, the Manu National Park in Peru (4000 hectare-survey) has 1300 species, while neighboring Tambopata National Park (5500 hectare-survey) has at least 1231 species

The researchers found that tropical plant species -- including species from Borneo, New Guinea, northeast Australia and South America -- had more than twice the rate of molecular evolution as closely related species in temperate parts of North America, southern Australia, Eurasia and New Zealand. Dr. Wright says the largest difference in the rate of molecular evolution encountered by the team was between New Zealand's kauri (Agathis australis) and the kauri from Borneo (Agathis borneensis).

Biodiversity is several magnitudes higher in the tropics than in temperate regions. For example, whereas temperate forests are often dominated by a half dozen tree species or fewer that make up 90 percent of the trees in the forest, a tropical rainforest may have more than 480 tree species in a single hectare (2.5 acres). A single bush in the Amazon may have more species of ants than the entire British Isles.

Of the world's twenty most biodiverse countries, 15 -- Brazil, Colombia, Indonesia, Mexico, Venezuela, Ecuador, India, Peru, Bolivia, Malaysia, Costa Rica, Thailand, Papua New Guinea, the Democratic Republic of Congo, and Madagascar -- feature predominantly tropical ecosystems. In recent years, deforestation of tropical rainforests and damage to coral reefs have spawned concerns among of biologists of an extinction crisis. Earlier this year, the U.N.'s Millennium Ecosystem Assessment warned that extinctions are presently running at 100 to 1,000 times the background rate.

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