“Large brains, small guts: The expensive tissue hypothesis supported within anurans”

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Wen Bo Liao, Shang Ling Lou, Yu Zeng, and Alexander Kotrschal

Two hypotheses regarding brain evolution are tested for the first time in anurans

Frogs with large brains have small guts but large eggs

Group spawning in Polypedates megacephalus, Beihai, Guangxi Zhuang Autonomous Region.
(Credit: Wen Bo Liao)

The brain is a very expensive organ, so it should be self-evident that if animals develop a larger brain they need to safe energy somewhere else. Already 20 years ago anthropologists suggested that the extra energy for evolving our own brains came from decreasing our gut size. After all, a larger brain does not need a large gut, because clever individuals should get access to higher quality food. As humans we may even have outsourced parts of gut to our cooking pots. This intuitive explanation for brain evolution was widely accepted even though data actually showing it remained scarce. A large study across 100 species of mammals published in Nature 5 years ago finally found no relationship between brain size and the gut, so it seemed like this idea did not hold up. But now a Chinese-Swedish team led by Dr. Wen Bo Liao from the China West Normal University has shown in 30 species of Chinese frogs that animals with larger brains indeed have smaller guts and vice versa. Because African fishes also show such a relationship, it seems as if what has been suggested but not found in mammals and other homeothermic animals holds true for ectotherms: that the gut and the brain are traded off against each other. The authors suggest that this is so because brain tissue should be relatively more expensive for ectothermic animals. Another result from this study is that the species with larger brains also lay larger eggs, which is common in many animal families. “Our results show that the evolution of brain size follows general patterns across vertebrates in some but not all respects,” Dr. Liao concludes. Currently Dr. Liao and his team are investigating whether the prey the larger-brained frogs feed on is indeed more cognitively challenging to catch and more nutritious. Read the Article