No evidence for the expensive-tissue hypothesis in the Asiatic toad (Bufo gargarizans)

Conferring cognitive ability on animals, the brain is one of the most metabolically costly organs in vertebrates, and thus a large amount of energy associated with brain tissue maintenance should constrain brain size evolution. The expensive-tissue hypothesis (ETH) states that decrease in the sizes of other metabolically costly tissues compensates for increase in brain. In this paper, we tested ETH in a single species, Bufo gargarizans. We found no negative correlation between brain weight and intestinal length and no negative correlation between brain weight and the weight of other organs (heart, lungs, stomach, liver, kidneys, spleen, and testes). Therefore, our results do not support the ETH. We also found that intestinal length, stomach weight, liver weight and kidneys weight were positively correlated with each other, which may reflect the close functional relationships among these organs. However, a negative correlation was found between intestinal length and testes weight, indicating a trade-off between the testes and gut. Our findings suggest that energetic cost of a large brain in this species cannot be compensated by decreasing weight of other expensive organs.

Automated summary

The study did not find a negative correlation between brain weight and the weight of other organs, which does not support the expensive-tissue hypothesis. Positive correlations were found among certain organs, suggesting close functional relationships among them. This indicates that the energetic cost of a large brain in this species cannot be offset by reducing the weight of other expensive organs.