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Evolution speeds up in the tropics

Tropical mammals are evolving faster than those found at high latitudes or elevations, according to a study published online today (June 23) in Proceedings of the Royal Society B. This pattern had previously been found in plants and marine protists but until now was assumed to apply only to cold-blooded organisms. Structure of DNA helixImage: Richard Wheeler, Wikimedia Commons "There's lots of reasons to believe that temperature plays a substantial role in generating [differences in the rate of

By | June 24, 2009

Tropical mammals are evolving faster than those found at high latitudes or elevations, according to a study published online today (June 23) in Proceedings of the Royal Society B. This pattern had previously been found in plants and marine protists but until now was assumed to apply only to cold-blooded organisms.
Structure of DNA helix
Image: Richard Wheeler,
Wikimedia Commons
"There's lots of reasons to believe that temperature plays a substantial role in generating [differences in the rate of evolution]," said evolutionary ecologist linkurl:James Brown;http://biology.unm.edu/jhbrown/ of the University of New Mexico, who did not participate in the study. "What's particularly interesting here is that [this same pattern] occurs in mammals, which take their body temperatures with them wherever they go around the world." That means, he said, that "this [difference] can't be a direct effect of temperature per se." In 1799, German naturalist and explorer Alexander von Humboldt noticed that there was greater species richness near the equator. Nearly two centuries later, evolutionary ecologist linkurl:Klaus Rohde;http://www-personal.une.edu.au/%7Ekrohde/ of University of New England in Australia suggested a mechanism. "At higher temperatures, mutations are more frequent and generation times are shorter," resulting in faster evolution, said Rohde, who was not involved in the research. This could in turn lead to higher rates of speciation, which could result in the greater species diversity found in the tropics. However, because they are able to regulate their body temperature independent of habitat, "the theory wasn't thought to apply to warm blooded animals," said ecologist linkurl:Gary Mittelbach;http://www.kbs.msu.edu/faculty/mittelbach/ of the Kellogg Biological Station in Michigan. Evolutionary biologist linkurl:Len Gillman;http://www.aut.ac.nz/study-at-aut/study-areas/sciences/our-people/len-gillman of Auckland University of Technology in New Zealand and colleagues compiled a global dataset of 130 pairs of closely related species whose ranges differed in either latitude or elevation. Comparing sequences of cytochrome b -- the most consistently available mammalian gene in the GenBank database -- for each of these pairs as well as two closely related species that served as reference points for the comparison, Gillman discovered that DNA substitution rates were substantially faster for those species that live at lower latitudes and elevations. "[It's] an empirical pattern that is begging for an explanation," Brown said. "The most likely mechanism, which would have to do with the effect of temperature, can't hold for bird and mammals" -- because they are both warm-blooded -- "so we've got to look else where for the explanation." The authors propose two reasons why even warm-blooded animals may evolve faster in warmer climates. The first, known as the Red Queen hypothesis, suggests that because the other organisms that interact with mammals, such as parasites and plants, are undergoing faster evolution, there is a coevolutionary pressure for mammals to keep up. "The biotic environment is changing more rapidly, and therefore the mammals are evolving more rapidly in response," Gillman said. Alternatively, behavioral adaptations to temperate climates, such as hibernation and torpor, may reduce the annual average metabolic rate of mammals at high latitudes and elevations. This in turn could decrease the chance of a germline mutation that may spread through the population. The paper can't distinguish between the two, Rohde said, but "I suspect the combination of both will be found for mammals." Gillman is now looking at the effects of water availability on the rate of evolution. "For most species," he said, "it's not just temperature that's important for species richness, it's productivity." Another area in need of research is the link between the rates of molecular evolution and the patterns of species richness. "No one knows whether these intriguing patterns of microevolutionary change are in fact going to be drivers of speciation," said Mittelbach. "So there's still a fundamental step here that's missing."
**__Related stories:__*** linkurl:Genetic evidence for punctuated equilibrium;http://www.the-scientist.com/news/display/25023/
[6th October 2006]*linkurl:Mutations go tick, tock;http://www.the-scientist.com/article/display/22296/
[20th July 2004]*linkurl:Evolution at warp speed;http://www.the-scientist.com/article/display/13205/
[19th August 2002]
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Comments

Avatar of: David Marshak

David Marshak

Posts: 2

June 24, 2009

Mammalian tested are at ambient, not body temperature.
Avatar of: MING ZHANG

MING ZHANG

Posts: 8

June 24, 2009

Interesting, but will life be also shorter? and will adolescence appear earlier?
Avatar of: Eric Olsen

Eric Olsen

Posts: 5

June 24, 2009

More oxygen and water vapor in atmosphere at lower altitudes?
Avatar of: Klaus Rohde

Klaus Rohde

Posts: 4

June 24, 2009

For further details on the hypothesis tested in this paper see:\n\nhttp://knol.google.com/k/klaus-rohde/latitudinal-gradients-in-species/xk923bc3gp4/56#\n\n\nhttp://knol.google.com/k/klaus-rohde/effective-evolutionary-time/xk923bc3gp4/11#
Avatar of: GREG PRONGER

GREG PRONGER

Posts: 9

June 25, 2009

One of the phenomenons we've observed with human evolution is the "Out of Africa" situation. This would seem to be evidence that we may also be subject to this phenomena.\n\nIs it simply that tropical areas offer greater "intra" and "inter" species competition? The article mentions temperate climates, and if it wasn't looked at, it may be worthwhile to compare the tropics to savanna (Africa).\n\nGreg
Avatar of: RAVI NAMBY

RAVI NAMBY

Posts: 17

June 27, 2009

evolution spped up IN THE TROPIC, AS MENTIONED IN THE ARTICLE, THE METABOLIC RATE, AND HENCE MUTATION CHANCE IS MORE IN TROPICS, OWING TO HIGH TEMPERATURE.\n\nTEMPERATURE INCREASES CELL ACTIVITIES, CAUSE MORE MOLECULER MOVEMENTS,WITH TEMPERATURRE AND HENCE MORE METABOLIIC ACTIVITIES, WHICH LEADS TO MUTATION
Avatar of: daniel miller

daniel miller

Posts: 40

June 29, 2009

Why isn't just increased competition with the greater number of living organisms and the increase in niche development enough to drive rapid evolution? Why do we need to postulate something that is increasing mutation?
Avatar of: JOHN COLLINS

JOHN COLLINS

Posts: 5

July 1, 2009

Are we back to the 50s movies with atomic bombs and giant mutant spiders? Who are these "experts" expecting a correlation with mutation rates and rates of evolutionary change?\n\nIt is unlikely that we can expect any direct correlation between mutation rate (per base/hour, say) and evolution rate. Sufficient variety accumulates in a population to ensure the variation that selection may operate on, later to be observed as evolutionary change. Organisms use DNA replication enzymes with fidelity levels that are compatible with their life expectancies and generation times: high for larger genomes and long life expectancies and low for small genomes and short replication times.\n\nOrganisms deviating from these present fidelity levels for the replication enzymes would be at a disadvantage, since higher levels of mutation would be lethal to the population. \nJohn Collins\nTU Braunschweig, Germany
Avatar of: Klaus Rohde

Klaus Rohde

Posts: 4

July 30, 2009

John Collins writes:\n\n"Sufficient variety accumulates in a population to ensure the variation that selection may operate on, later to be observed as evolutionary change"\n\nWhat is sufficient? The point is that diversity is different at different latitudes. The higher the temperatures, the higher diversity. Correlated with diversity (not necessarily a simple linear correlation) are temperature, generation times and probably speed of selection. There is evidence that temperature increases mutation rates, and there is evidence that shorter generation times also do.
Avatar of: Klaus Rohde

Klaus Rohde

Posts: 4

July 30, 2009

daniel miller writes:\n\n"Why isn't just increased competition with the greater number of living organisms and the increase in niche development enough to drive rapid evolution? Why do we need to postulate something that is increasing mutation?"\n\nIncreased competition is a consequence of greater species diversity and not vice versa. It seems fairly obvious that a greater diversity will lead to more competition. - In other words, competition cannot be the primary driving factor for increasing diversity,although it may well be a secondary factor (a sort of snowball effect).
Avatar of: Klaus Rohde

Klaus Rohde

Posts: 4

July 30, 2009

Once more John Collins:\n"Organisms deviating from these present fidelity levels for the replication enzymes would be at a disadvantage, since higher levels of mutation would be lethal to the population."\n\nIt is well known of course that "higher levels of mutation" can be lethal to a population. But not always, it seems that in the tropics populations run greater risks but overall are propelled to greater diversity. A few always manage to do well and perhaps better.

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