Trade-offs between growth and self-maintenance are common in nature, such that early-life effects on growth can generate lasting consequences on survival and longevity. Telomeres – putative biomarkers of self-maintenance – may link early growth with these later phenotypic effects, but evidence for growth-telomere trade-offs is mixed. Null or even positive relationships between growth and telomeres may be driven by heterogeneity in resource availability or invariable allocation towards telomere maintenance within a population. We used nestling tree swallows (Tachycineta bicolor) to assess the directionality and timing of relationships between growth and telomere length in several tissues. We focused on two important phases of growth: first, the peak of postnatal growth occurring around 6-days old when nestlings grow by ~33% in a single day, and subsequently, the later phase of growth occurring as body mass plateaus near adult size at 12-days old. We quantified telomere attrition in blood during postnatal growth, as well as telomere length in the blood, brain, adrenals, and liver at 12-days old. Growth was unrelated to telomere length in the liver and telomere dynamics in blood. However, brain telomere length was positively correlated with peak growth, and adrenal telomere length was positively related to later growth, particularly for chicks that had experienced a temporary stressor. These observations suggest that variation in resource availability may mask trade-offs, generating positive correlations between growth and telomere length at the population level. They also provide insights into complex relationships between growth and self-maintenance that can be revealed by looking in multiple tissues.

We attempted to manipulate chick peak growth by injecting mothers with lipopolysaccharide (LPS), which tends to decrease provisioning, in order to assess potential intergenerational effects on chick growth and telomere dynamics. When chicks were 5 or 6-days old, we injected their mothers with either saline or LPS, and quantified changes in maternal mass and visitation rate (using RFID) to control for maternal variation in responses when looking at the magnitude of effects on chicks.

For chicks, we measured mass just prior to maternal injections, 24h after maternal injections, and when chicks were 12-days old. From this data, we calculated changes in mass (absolute and/or %), including changes during a chick's typical peak of growth (i.e. from 5 to 6-days old) and later growth (i.e. from 6 to 12-days old). In order to quantify changes in blood telomere length, we also collected blood samples from chicks at the start of the study (5 to 6-days old) and when chicks were 12-days old. To assess the relationship between postnatal growth and telomere length in non-blood tissues, we euthanized one median-massed chick from each nest at the end of the study and collected blood, brain, liver, and adrenals (n = 21 chicks).

*While our published study does not include this data, we also collected chick wing morphology (length, primary feather emergence) as well as molecular sex. 

DNA from all tissues was extracted using a Promega Maxwell RSC instrument, and telomere length was quantified for all DNA using qPCR. This dataset uses either 2^deltadelta Ct values (for relative telomere length of non-blood tissues) or a corrected change in telomere length (corrected for regression to the mean) for blood samples. Blood telomere metrics were log-transformed to achieve normality.

Please see Materials & Methods of this paper for further details.