Analyses of TL and life history traits
TROC was significantly but moderately negatively associated withAdult TL and Chick TL (respectively; r = -0.349, P = 0.04,
n = 34; r = 0.514, P < 0.01, n = 24). However, the association
of TROC and Adult TL was strongly influenced by two
extreme points, Larus Andouiin i and Parus major , which
presented long telomere lengths and high rates of annual erosion (ESM
1). If we exclude these two extremes, the association changed in sign
and became non-significant (r = 0.127, P = 0.48, n = 32). Adult
TL and Chick TL showed a strong positive association (r = 0.883.
P < 0.0001, n = 28).
Using the scores of the different avian species on the principle
components, we investigated the associations of TL with the three
statistically independent life history axes. The three telomere
variables (Adult TL , TROC and Chick TL ) showed
small to medium and non-significant associations with phylogeny (Figure
2). Body size and the slow-fast continuum of pace of life (PC1, PC2)
were strongly and significantly associated with the phylogenetic
pattern. Parental care (PC3) exhibited a small-to-medium association
with phylogeny, but a significant one.
We then investigated the associations of bird TL with the three
principle component axes (that displayed phylogenetic patterns) using
three different approaches. First, we explored direct Pearson’s
correlations (without considering any phylogenetic effect) between TL
variables and the principle components. This suggested a small-to-medium
and non-significant correlation of Adult TL with body size (PC1;
Table 2A, Figure 3A). TROC exhibited a medium positive
association with body size (PC1) and a large negative association with
the slow-fast pace of life (PC2; species greater reproduction and
shorter life exhibited more strongly negative TROC ; Table 2B,
Figure 4A, B). Correlations were at best small and non-significant
between Chick TL and the life-history axes (Table 2C, Figure 5).
Next, univariate analyses that statistically adjusted both telomere
variables and life-history data for the phylogenetic pattern confirmed
only some of the ahistorical correlational analyses. First, it revealed
that the relatively weak pattern of association of Adult TL and body
size was likely due to the phylogenetic pattern (the residual
“phylogeny-adjusted” correlation was -0.153; Table 2A). The same was
evident for the moderate positive association of TROC with body
size (the residual correlation was -0.108; Table 2B). The negative
association of TROC and the slow-fast pace of life was confirmed
as a strong pattern. Association between TROC and life-history
axes exhibited especially strong phylogenetic patterns.
We next examined these potential associations while considering the
effect of phylogeny on both variance and co-variance of TL and PC
variables, using a multivariate phylogenetic framework. The correlation
between PCs and TL variables due to phylogeny were marginal,
since their posterior distributions mostly were broadly centred on or
largely overlapped zero (Table 2, Figure 6). Only the negative
association of TROC and slow-fast pace of life approached
significance, and it again exhibited a strong phylogenetic pattern
(Table 2B; Figure 6, center-panels).
Finally, we investigated whether relationships among PC axis and TL
variables might differ among avian orders. We found that the association
of Adult TL and the slow-fast pace of life (PC2) was
significantly positive in the Passeriiformes (r = 0.690, t = 3.321, p =
0.006, n = 14). However, in the Procellariiformes the association was
negative (r = -0.754, t = -2.812, p = 0.031, n = 8), i.e.opposite to the general non-significant inter-specific trend (Figure
3B). TROC and PC1 and PC2 axes were significantly and negatively
correlated in the Procellariiformes (Figure 4; PC1: r = -0.951, t =
-6.872, p < 0.001; PC2: r = -0.890, t = -4.368, p = 0.007; all
n = 7). No significant correlations were found within orders for PC axes
and Chick TL (Figure 5, all p > 0.25).