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.
Early-life telomere length (TL) is associated with fitness in a range of organisms. Little is known about the genetic basis of variation in TL in wild animal populations, but to understand the evolutionary and ecological significance of TL it is important to quantify the relative importance of genetic and environmental variation in TL. In this study, we measured TL in 2746 house sparrow nestlings sampled across 20 years and used an animal model to show that there is a small heritable component of early-life TL (h2=0.04), but with a strong component of maternal inheritance. Variation in TL among individuals was mainly driven by environmental (year) variance, but also brood and parental effects. We did not find evidence for a negative genetic correlation underlying the observed negative phenotypic correlation between TL and structural body size. Thus, TL may evolve independently of body size and the negative phenotypic correlation is likely to be caused by non-genetic environmental effects. We further used genome‐wide association analysis to identify genomic regions associated with TL variation. We identified several putative genes underlying TL variation; these have been inferred to be involved in oxidative stress, cellular growth, skeletal development, cell differentiation and tumorigenesis in other species. Together, our results show that TL is a lowly heritable, polygenic trait which is strongly affected by environmental conditions in a free-living bird.
Telomeres, the short repetitive DNA sequences that cap the ends of linear chromosomes, shorten during cell division and are implicated in senescence in most species. Telomerase can rebuild telomeres but is repressed in many mammals that exhibit replicative senescence, presumably as a tumor suppression mechanism. It is therefore important that we have an accurate understanding of the co-evolution of telomere biology and life-history traits that has shaped the diversity of senescence patterns across species. Gomes et al. (2011) produced a large data set on telomere length (TL), telomerase activity, body mass and lifespan among 57 mammal species. We re-analyzed their data using the same phylogenetic multiple regressions and with several additional analyses to test the robustness of findings. We found substantial inconsistencies in our results compared to Gomes et al.’s. Consistent with Gomes et al. we found an inverse association between TL and lifespan. Contrary to the analyses in Gomes et al., we found a generally robust inverse association between TL and mass, and only weak non-robust evidence for an association between telomerase activity and mass. These results suggest that shorter TL may have been selected for in larger and longer-lived species–likely as a mechanism to suppress cancer. We support this hypothesis by showing that longer telomeres predict higher cancer risk across 22 species. Furthermore, we find that domesticated species have longer telomeres. Our results call into question past interpretations of the co-evolution of telomere biology and life-history traits and stress the need for careful attention to model construction.