No evidence for the 'expensive-tissue hypothesis' in the dark-spotted frog, Pelophylax nigromaculatus

Abstract

Increased brain size significantly contributes to the performance and fitness of organisms. The expensive-tissue hypothesis (ETH) based on studies of the correlation between brain size and size of the other energetically costly organs in mammals predicts that energy investment increased in one energetically costly tissue necessitates a decrease of investments in other costly tissues. Here, we test this hypothesis in an ectothermic species, the dark-spotted frog, Pelophylax nigromaculatus . We found that relative brain size was not correlated with relative sizes of testes, heart, liver, spleen, kidneys or limb muscles within each sex. Moreover, we also failed to find significantly negative correlation among the expensive organs (i.e. testes, heart, liver, spleen, kidneys or limb muscles) in this frog. However, we observed a significantly positive correlation between liver residuals and kidney residuals. Our finding suggests that energetic costs of one expensive tissue do not direct necessarily affect the investment in another expensive tissue, but rather may scatter its effect on all other expensive tissues.