A evolução é mais inteligente do que você idiota, mesmo quando for características inúteis...

domingo, setembro 13, 2009

Evolutionary Fate Of 'Useless' Traits: Why Some Traits Break Down Quickly While Others Persist Over Time

ScienceDaily (Sep. 11, 2009) — What happens when traits no longer give creatures a competitive edge?

Some subterranean animals that live in darkness function perfectly well without eyesight, for example. And the tiny leg bones buried in the backs of whales — left over from their land-dwelling ancestors — don't get much action in the ocean.
In a recent review, researchers teamed up to take a closer look at the evolutionary fate of useless traits. Supported by the National Evolutionary Synthesis Center (NESCent) in Durham, NC, their aim was to examine what happens to traits that are no longer needed. "Just about everybody who thinks about trait evolution focuses on traits that are beneficial," writes first author David Lahti, a biologist at Queens College. "But few people think about traits that are useless, or that are becoming less useful over time."

For example, the ability to recognize and flee from enemies becomes less critical in predator-free habitats. "There are many examples of animals that were once subject to predation, but have since been introduced to areas where predators are absent or have been killed off," Lahti says. In these cases, studies show that traits which were once key to survival – vigilance, caution, speed and agility – start to erode over time. "Things like alertness, having to run fast, having to fly — many predator avoidance traits end up being useless to those animals," Lahti says.

Under an evolutionary phenomenon called relaxed selection, traits that were advantageous in one time and place become obsolete in another. Traits that aren't actively maintained by natural selection tend to become smaller or less functional over time, studies suggest. The researchers wanted to know why some traits break down quickly, while others take longer to go away. "All traits will eventually disappear if they have no function," Lahti explains. "The question we're asking now is: how do you know how fast that will happen?"

To answer this question, the researchers scoured the literature for examples of relaxed selection. After reviewing more than 80 studies spanning nearly 150 years of research, they pinpointed several factors that determine how quickly traits are lost. "Numerous cases of trait loss illustrate that evolution isn't necessarily progressive," says co-author Norman Johnson of the University of Massachusetts. "It seems that not all the same evolutionary rules are followed when you're losing a trait as when you're gaining it," Lahti adds.

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Relaxed selection in the wild

David C. Lahti1, , Norman A. Johnson2, Beverly C. Ajie3, Sarah P. Otto4, Andrew P. Hendry5, Daniel T. Blumstein6, Richard G. Coss7, Kathleen Donohue8 and Susan A. Foster9

1Department of Biology, University of Massachusetts, Amherst, MA 01003, USA

2Department of Plant, Soil, and Insect Sciences, University of Massachusetts, Amherst, MA 01003, USA

3Center for Population Biology, University of California, Davis, CA 95616, USA

4Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada

5Redpath Museum and Department of Biology, McGill University, Montreal, QC H3A 2K6, Canada

6Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA

7Department of Psychology, University of California, Davis, CA 95616, USA

8Department of Biology, Duke University, Durham, NC 02138, USA

9Department of Biology, Clark University, Worcester, MA 01610, USA

Available online 8 June 2009.

Natural populations often experience the weakening or removal of a source of selection that had been important in the maintenance of one or more traits. Here we refer to these situations as ‘relaxed selection,’ and review recent studies that explore the effects of such changes on traits in their ecological contexts. In a few systems, such as the loss of armor in stickleback, the genetic, developmental and ecological bases of trait evolution are being discovered. These results yield insights into whether and how fast a trait is reduced or lost under relaxed selection. We provide a prospectus and a framework for understanding relaxed selection and trait loss in natural populations. We also examine its implications for applied issues, such as antibiotic resistance and the success of invasive species.

Article Outline

What is relaxed selection?
A spotty history
Influences on a trait under relaxed selection
Direct fitness benefits and costs
Trait correlations: indirect benefits and costs
Neutral factors
Consequences for trait expression and evolution
Trait persistence or functional modification
Plastic loss of expression
Trait loss or vestigialization
Conclusions
Acknowledgements
References

Source/Fonte.

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Este artigo do Trends in Ecology and Evolution, 2009; 24(9): 487-496 pode ser lido gratuitamente por professores, pesquisadores e alunos de universidades públicas e privadas com acesso ao site CAPES/Periódicos.