Changes in telomere dynamics could underlie life-history trade-offs
among growth, size and longevity, but our ability to quantify such
mechanistic processes in natural, unmanipulated populations is limited.
We investigated how 4 years of artificial selection for either larger or
smaller body size affected early-life telomere length in two insular
populations of wild house sparrows. A negative correlation between
telomere length and structural size was evident under both selection
regimes. The study also revealed that male sparrows had longer telomeres
than females, after controlling for size, and there was a significant
negative effect of harsh weather conditions on telomere length. The
long-term fitness consequences of these changes in early-life telomere
length induced by the artificial size selection were explored over a
period of 11 years. These analyses indicated disruptive selection on
telomere length because both short and long early-life telomere length
tended to be associated with the lowest mortality rates and highest life
expectancy. There was also weak evidence for a negative association
between telomere length and annual reproductive success, but only in the
population where body size was increased experimentally. Our results
suggest that natural selection for optimal body size in wild animals
will affect early-life telomere length during growth, which is known to
be linked to longevity in birds, but also that the importance of
telomeres for long-term somatic maintenance and fitness is complex in a
wild bird species.