Replication of analyses in Gomes et al. (2011)
Presented in Table 1 are the results reported by Gomes et al. (2011) and our re-analysis – both using two phylogenetic multiple regression models. Consistent with Gomes et al. (2011), we found that both mass and TL significantly predicted lifespan. However, the remaining results are all substantially discordant. While Gomes et al. (2011) found no association between telomerase activity and lifespan, we observed a significantly positive association. In predicting body mass, Gomes et al. (2011) found that telomerase activity was a significant predictor, but TL was not. We found the opposite: telomerase activity did not predict mass, but longer TL predicted decreased body mass. Using current estimates for mass and lifespan from the AnAge database (Table S9) did not qualitatively alter the findings described above except the association between telomerase activity and lifespan was attenuated (β=0.0036, p=0.0594, Table S2).
Gomes et al. (2011) reported a series of bivariate plots (their Fig. 4) for key variables in their analyses along with p-values. These p-values are identical to those presented in their Fig. 2 (our Table 1), strongly suggesting that these significance values were from phylogenetic multiple regressions, not phylogenetic bivariate regressions. A casual reader is likely to interpret these p-values as bivariate associations. Here, we present phylogenetic linear bivariate regression analyses of TL, body mass, maximum lifespan, and telomerase activity to examine the sensitivity of the multiple regression results and more clearly define these bivariate associations.
The bivariate results (Fig. 1) are qualitatively consistent with our multiple regression results, except lifespan did not show any association with telomerase activity (Fig. 1d). Based on these bivariate results, a 1% increase in body mass predicts a 0.08% decrease in TL (Fig. 1a), while a 1% increase in lifespan predicts a 0.43% reduction in TL (Fig. 1b). The co-evolution of TL and body mass is illustrated in the phylogeny in Fig. 2.
In an effort to further reconstruct the reasons for our discrepant results with those of Gomes et al. and explore the sensitivity of our analyses to modeling strategies, we experimented with alternative transformations of the telomerase activity measurements (see Supporting Information). Briefly, we find that in multiple regression models, as telomerase activity is first log-transformed (Table S3) and then binary transformed (Table S4), TL becomes less and less predictive of either mass or lifespan and the correlation between TL and telomerase activity increases (Table S5). When the bivariate association of mass predicting binary telomerase activity (0/1) is modelled in a phylogenetic logistic regression (see Supporting Information), complete telomerase repression is significantly associated with higher body mass with an inflection point at 0.8 kg (Fig. S1).