Como que as baleias 'evoluíram' em 35 milhões de anos?

segunda-feira, maio 31, 2010

How Whales Have Changed Over 35 Million Years

ScienceDaily (May 31, 2010) — Whales are remarkably diverse, with 84 living species of dramatically different sizes and more than 400 other species that have gone extinct, including some that lived partly on land. Why are there so many whale species, with so much diversity in body size?

Humpback whale. (Credit: iStockphoto/Josh Friedman)

To answer that, UCLA evolutionary biologists and a colleague used molecular and computational techniques to look back 35 million years, when the ancestor of all living whales appeared, to analyze the evolutionary tempo of modern whale species and probe how fast whales changed their shape and body size. They have provided the first test of an old idea about why whales show such rich diversity.

"Whales represent the most spectacularly successful invasion of oceans by a mammalian lineage," said Michael Alfaro, UCLA assistant professor of ecology and evolutionary biology, and senior author of the new study, which was published this month in the early online edition ofProceedings of the Royal Society B and will appear at a later date in the journal's print edition. "They are often at the top of the food chain and are major players in whatever ecosystem they are in. They are the biggest animals that have ever lived. Cetaceans (which include whales, as well as dolphins and porpoises) are the mammals that can go to the deepest depths in the oceans.

"Biologists have debated whether some key evolutionary feature early in their history allowed whales to rapidly expand in number and form," Alfaro said. "Sonar, large brains, baleen (a structure found in the largest species for filtering small animals from sea water) and complex sociality have all been suggested as triggers for a diversification, or radiation, of this group that has been assumed to be rapid. However, the tempo -- the actual rate of the unfolding of the cetacean radiation -- has never been critically examined before. Our study is the first to test the idea that evolution in early whales was explosively fast."

Read more here/Leia mais aqui: Science Daily


Diversity versus disparity and the radiation of modern cetaceans

Graham J. Slater1,*†, Samantha A. Price2,*†‡, Francesco Santini1 and Michael E. Alfaro1

-Author Affiliations

1Department of Ecology and Evolutionary Biology, University of California at Los Angeles, Los Angeles, CA 90025, USA

2National Evolutionary Synthesis Center (NESCent), 2024 West Main Street, Suite A200, Erwin Mills Building, Durham, NC 27705, USA

*Authors for correspondence (;


Modern whales are frequently described as an adaptive radiation spurred by either the evolution of various key innovations (such as baleen or echolocation) or ecological opportunity following the demise of archaic whales. Recent analyses of diversification rate shifts on molecular phylogenies raise doubts about this interpretation since they find no evidence of increased speciation rates during the early evolution of modern taxa. However, one of the central predictions of ecological adaptive radiation is rapid phenotypic diversification, and the tempo of phenotypic evolution has yet to be quantified in cetaceans. Using a time-calibrated molecular phylogeny of extant cetaceans and a morphological dataset on size, we find evidence that cetacean lineages partitioned size niches early in the evolutionary history of neocetes and that changes in cetacean size are consistent with shifts in dietary strategy. We conclude that the signature of adaptive radiations may be retained within morphological traits even after equilibrium diversity has been reached and high extinction or fluctuations in net diversification have erased any signature of an early burst of diversification in the structure of the phylogeny.

adaptive radiation     body size    Cetacea    disparity   diversity


↵† These authors contributed equally to this work and should be considered joint first authors.

↵‡ Present address: Department of Evolution and Ecology, University of California at Davis, Davis, CA 95616, USA.
Received February 26, 2010.
Accepted April 30, 2010.

© 2010 The Royal Society


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