We make the assumption that factors such as generation time and longevity did not differ greatly among samples/populations; this was not possible to measure, but it seems reasonable.
In particular, body size, generation time and longevity have been shown to be associated with substitution rates [ 27, 28, 34].
While the non-synonymous data are noisier, with generation time and longevity effects not reaching individual significance, the slopes of the regressions are very similar (Table 1), and body mass is again favoured over maximum lifespan in multiple regression (Table 3).
This has been noted in previous phylogenetic reconstructions and different explanations have been proposed, including differences in generation times and longevity, but recent analyses suggest that mutation rates differ for mtDNA between different mammal lineages [73].
The life-history traits that scale with substitution rates in mammals (generation time, fecundity, and longevity) also correlate tightly with body size [ 57- 59].
It has been suggested that both generation time (which is linked to longevity) and the rate of apical growth (which is linked with the rate of mitosis) are negatively related to DNA substitution rate in plants [ 20].
Species numbers for each clade are given in Additional File 1. Substitution rates in mammals are known to be influenced by a number of life history variables, including generation time [ 29], fecundity [ 27], and longevity [ 57].
Our results instead are suggestive of a more complex selective force shaping the evolution of these genes that is likely to incorporate variation across species in demography, metabolic rate, germ line generation time, as well as body size and longevity.
Placental mammals display a huge range of life history traits, including size, longevity, metabolic rate and germ line generation time.
Longevity, age of sexual maturity and (by extension) generation time are, on average, longer in subterranean rodents than in their surface counterparts [ 12, 25, 26] (Additional file 1: Table S10 and Additional file 2: Fig. S1).
