Figure 1.

Hypothetical proportion of telomere length variation among individuals explained by genetic (blue) and environmental (green) effects: (a) in a population where individuals experience: (1) highly variable environments versus (2) relatively constant environments; and (b) estimated using mixed models of increasing complexity, based on repeated measures of telomere length per individual: model (3) a mixed model to separate individual variation from environmental (residual) variation, model (4) an ‘animal’ model where individual variation is separated into additive genetic and permanent environmental effects, and model (5) where maternal identity is included to estimate maternal effects.