Comments on: Scientists breed smarter fish but reveal costs of big brains

By: Peter Klaren

Peter Klaren — Sun, 13 Jan 2013 16:38:26 +0000

I guess for _any_ animal, small- or large-brained, a reduced but adequate gut is beneficial. Small savings in energy budget confer large favourable selection pressure (see study by Dykhuizen on E. coli, published in Evolution in 1978).

By: Quercus

Quercus — Mon, 07 Jan 2013 19:14:55 +0000

I’m not sure that ‘flirt with extinction’ is the best way to describe the ‘grey ceiling’. That kind of implies something other than natural selection forcing larger brains (like the unscientific ‘Irish Elk antlers got too big, so they died out’). Of course the species won’t go extinct if it’s brain size is near the ceiling; rather, the individuals with the largest brains who spend too much on brains and too little on reproduction won’t reproduce, and the remaining individuals carry on the species with an average brain size below the ceiling. May I suggest instead:

“..a ‘grey ceiling’ for animals— a point where they can’t put any more resources towards brains and still reproduce successfully.”

By: Jonathan Pettitt

Jonathan Pettitt — Sat, 05 Jan 2013 09:52:20 +0000

This is an interesting study, but I’m not convinced that it unequivocally proves the expensive tissue hypothesis. The changes that they observe over only two generations are most likely caused by pleiotropy, with the alleles responsible for increased brain size having a negative effect on gut size and fertility. The important question is what causes this pleiotropy? It could be adaptive: selection for alleles that inversely correlate brain size with gut size and fertility caused by the trade offs involved in the cost of maintaining a large brain; but it could also have evolved neutrally. I’m not sure how you would test which of these two possibilities is correct, as is often the case for proposed adaptive features.

By: Chris M.

Chris M. — Fri, 04 Jan 2013 20:41:37 +0000

@Dwayne, the problem is that that would probably require ramping up the metabolism of digestion quite a bit, which may not be as easy to do as increasing neuronal proliferation. If you selected for larger brains for long enough, you might see an increased caloric intake begin to support them and other organs would return toward normal. Selecting for multiple things at once is likely to require a longer selection period to see both change.

I’ve often wondered whether captive guppies in general have a higher metabolism; after dozens of generations in captivity with consistent food access, it seems like this would be a useful adaptation.

By: Baka Karasu

Baka Karasu — Thu, 03 Jan 2013 22:34:02 +0000

For further reading on how/why humans developed larger brains I highly recommend Susan Blackmore’s meme/gene coevolution themes in “Meme Machine”

By: dwayne stephenson

dwayne stephenson — Thu, 03 Jan 2013 17:34:01 +0000

Why wouldn’t guppies just eat more to maintain their other organs? If guppy variants are mostly just shifting cell loads around, interpreting these results may not be as easy as this article makes it out to be.