Big Brains Are Pricey, Guppy Study Shows

Jan. 3, 2013 — Bigger brains can make animals, well, brainier, but that boost in brain size and ability comes at a price. That’s according to new evidence reported on January 3rd inCurrent Biology, a Cell Press publication, in which researchers artificially selected guppies for large and small brain sizes.


 

The findings lend support to the notion that bigger brains and increased cognitive ability do go together, a topic that has been a matter of considerable debate in recent years, said Niclas Kolm of Uppsala University in Sweden. They also represent some of the first convincing evidence that large brains are expensive, evolutionarily speaking.

“We provide the first experimental evidence that evolving a larger brain really is costly in terms of both gut investment and, more importantly, reproductive output,” Kolm said.

Together, the findings strongly support the idea that relative brain sizes among species are shaped through a balance between selection for increased cognitive ability and the costs of a big brain.

The results in guppies have important implications for us humans. After all, one of the most distinctive features of the human brain is its large size relative to the rest of the body.

“The human brain only makes up 2 percent of our total body mass but stands for 20 percent of our total energy demand,” Kolm said. “It is a remarkably costly organ energetically.”

But support for the so-called “expensive-tissue hypothesis” — that there is a trade-off between the brain and the energy demands of other organs and reproduction — came only from comparative studies among species and were correlative in nature.

In the new study, Kolm’s team took a different, within-species approach. They selected live-bearing guppies for large and small brains relative to the size of their bodies. Under that strong selection pressure, they found that brain size could evolve “remarkably quickly.”

After selection, large-brained guppies outscored their smaller-brained peers in a test of numerical learning. With more energy devoted to brain-building, brainy fish — males especially — did have smaller guts. They also left fewer offspring to the next generation.

Those effects were observed despite the fact that the fish were supplied with an abundance of food. The researchers say they are curious to see what will happen in future experiments with fish in a more competitive, semi-natural environment including limited resources and predators.

The findings lead Kolm and his colleagues to suggest that the relatively small family sizes of humans and other primates, not to mention dolphins and whales, might have helped to make our big brains possible.


Story Source:

The above story is reprinted from materials provided byCell Press, via EurekAlert!, a service of AAAS.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. Alexander Kotrschal, Björn Rogell, Andreas Bundsen, Beatrice Svensson, Susanne Zajitschek, Ioana Brännström, Simone Immler, Alexei A. Maklakov, Niclas Kolm. Artificial selection on relative brain size in the guppy reveals costs and benefits of evolving a larger brainCurrent Biology, 2013 DOI:10.1016/j.cub.2012.11.058
 

 

Cell Press (2013, January 3). Big brains are pricey, guppy study shows. ScienceDaily. Retrieved January 9, 2013, from http://www.sciencedaily.com/releases/2013/01/130103131110.htm
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Evolutionary Increase in Size of the Human Brain Explained: Part of a Protein Linked to Rapid Change in Cognitive Ability

ScienceDaily (Aug. 16, 2012) — Researchers have found what they believe is the key to understanding why the human brain is larger and more complex than that of other animals.

(Credit: http://www.jokeroo.com/pictures/funny/brain-phone.html)

 

The human brain, with its unequaled cognitive capacity, evolved rapidly and dramatically.

“We wanted to know why,” says James Sikela, PhD, who headed the international research team that included researchers from the University of Colorado School of Medicine, Baylor College of Medicine and the National Institutes of Mental Health. “The size and cognitive capacity of the human brain sets us apart. But how did that happen?”

“This research indicates that what drove the evolutionary expansion of the human brain may well be a specific unit within a protein — called a protein domain — that is far more numerous in humans than other species.”

The protein domain at issue is DUF1220. Humans have more than 270 copies of DUF1220 encoded in the genome, far more than other species. The closer a species is to humans, the more copies of DUF1220 show up. Chimpanzees have the next highest number, 125. Gorillas have 99, marmosets 30 and mice just one. “The one over-riding theme that we saw repeatedly was that the more copies of DUF1220 in the genome, the bigger the brain. And this held true whether we looked at different species or within the human population.”

Sikela, a professor at the CU medical school, and his team also linked DUF1220 to brain disorders. They associated lower numbers of DUF1220 with microcephaly, when the brain is too small; larger numbers of the protein domain were associated with macrocephaly, when the brain is too large.

The findings were reported today in the online edition of TheAmerican Journal of Human Genetics. The researchers drew their conclusions by comparing genome sequences from humans and other animals as well as by looking at the DNA of individuals with microcephaly and macrocephaly and of people from a non-disease population.

“The take home message was that brain size may be to a large degree a matter of protein domain dosage,” Sikela says. “This discovery opens many new doors. It provides new tools to diagnose diseases related to brain size. And more broadly, it points to a new way to study the human brain and its dramatic increase in size and ability over what, in evolutionary terms, is a short amount of time.”

 


Story Source:

The above story is reprinted from materials provided byUniversity of Colorado Denver, via EurekAlert!, a service of AAAS.


Journal Reference:

  1. Laura J. Dumas, Majesta S. O’Bleness, Jonathan M. Davis, C. Michael Dickens, Nathan Anderson, J.G. Keeney, Jay Jackson, Megan Sikela, Armin Raznahan, Jay Giedd, Judith Rapoport, Sandesh S.C. Nagamani, Ayelet Erez, Nicola Brunetti-Pierri, Rachel Sugalski, James R. Lupski, Tasha Fingerlin, Sau Wai Cheung, James M. Sikela.DUF1220-Domain Copy Number Implicated in Human Brain-Size Pathology and EvolutionThe American Journal of Human Genetics, 2012; DOI:10.1016/j.ajhg.2012.07.016
Citation:

University of Colorado Denver (2012, August 16). Evolutionary increase in size of the human brain explained: Part of a protein linked to rapid change in cognitive ability. ScienceDaily. Retrieved August 19, 2012, from http://www.sciencedaily.com/releases/2012/08/120816141537.htm