A test of the metabolic theory of ecology with two longevity data sets reveals no common cause of scaling in biological times

Abstract

1. The metabolic theory of ecology (MTE) predicts that biological times should universally scale to body mass M as M0.25. However, support for this prediction came principally from non-phylogenetically controlled studies, whereas more recent analyses, which take the degree of shared ancestry between species into account, have revealed that both length of the gestation period and time to first reproduction do not follow this rule. 2. In the present study, we test this prediction of MTE on maximum longevity using two commonly accessible sources of information in zoology and ecology (AnAge and PanTHERIA data bases) that allow us to assess the scaling relation of longevity in more than 1200 mammalian species. We performed our analyses using both ordinary least square (OLS) and phylogenetic generalized least square (PGLS) regressions to assess the importance of controlling for phylogeny in such analyses. 3. Our results revealed clear discrepancies between analyses using the AnAge and PanTHERIA data bases. The scaling of longevity was consistently higher with the PanTHERIA than with the AnAge data base. However, we found that with both data sets, PGLS models performed better than OLS models, and the scaling exponent of longevity is, in nearly all cases, lower than the exponent of 0.25 predicted by the MTE. In addition, we provided evidence that gestation length and longevity do not scale isometrically (i.e. with a scaling exponent of 1.0) with each other as we would expect if these two life history traits had – perhaps due to the same biological principle – the same scaling exponent. 4. Our findings contradict the MTE and suggest that more complex processes than simple relationships with metabolism or body size control the evolution of longevity. Moreover, they reveal differences in relationships of gestation length and longevity that are probably tightly dependent on phylogeny.