Telomeres are emerging as correlates of fitness-related traits and may be important mediators of ecologically relevant variation in life history strategies. Growing evidence suggests that telomere dynamics can be more predictive of performance than length itself, but very little work considers how telomere regulatory mechanisms respond to environmental challenges or influence performance in nature. Here, we combine observational and experimental datasets from free-living tree swallows (Tachycineta bicolor) to assess how performance is predicted by the telomere regulatory gene POT1, which encodes a shelterin protein that sterically blocks telomerase from repairing the telomere. First, we show that lower POT1 gene expression was associated with higher female quality, i.e. earlier breeding and heavier body mass. We next challenged mothers with an immune stressor (lipopolysaccharide injection) that led to ‘sickness’ in mothers and 24h of food restriction in their offspring. While POT1 did not respond to maternal injection, females with lower constitutive POT1 gene expression were better able to maintain feeding rates following treatment. Maternal injection also generated a one-day stressor for chicks, which responded with lower POT1 gene expression and elongated telomeres. Other putatively stress-responsive mechanisms (i.e. glucocorticoids, antioxidants) showed marginal responses in stress-exposed chicks. Model comparisons indicated that POT1 mRNA abundance was a largely better predictor of performance than telomere dynamics, indicating that telomere regulators may be powerful modulators of variation in life history strategies.

We test the hypothesis that telomere regulatory mechanisms respond to stress and predict performance in wild animals, evaluated with a focus on POT1 ('protection of telomeres 1'). First, we ask whether POT1 gene expression is associated with three markers of individual quality in breeding female tree swallows (Tachycineta bicolor), including first egg date, body mass, and wing length (Winkler et al., 2020). We captured females and measured their body mass and wing length when they were rearing approx. 5-day old chicks. At the same time, we also collected whole blood samples from each female for telomere length and POT1 gene expression analyses. Second, we experimentally disrupted relationships between POT1 and performance by exposing breeding females to an ecologically relevant stressor (lipopolysaccharide injection), which leads to ‘sickness’ in mothers, and 24h of food restriction in their offspring. We assessed whether a female's telomere length and/or POT1 gene expression predicted fluctuations in body mass and visitation rates following injections. We also assessed effects of this stressor on their offspring. We measured chick growth and key aspects of telomere biology (i.e. change in relative telomere length, POT1 gene expression), as well as other traits that have been linked to telomere dynamics in previous work (i.e. glucocorticoids, antioxidants), mostly sampled one week after maternal injections. Last, we recorded fledging success and recruitment of chicks into the breeding population to assess whether telomere length and/or POT1 gene expression predict survival-related metrics.

Female visitation rates: We quantified maternal visitation to the nest using PIT tags and RFID readers positioned at the entrance of the nest box.

Relative telomere length: DNA was extracted from whole blood using a Promega Maxwell RSC instrument, and telomere length was quantified using qPCR. For questions relating to changes in chick telomere length over time, we use a corrected metric accounting for initial telomere length at 5-days old (corrected for regression to the mean).

Gene expression: RNA was extracted using a Trizol-based method. We then quantified antioxidant and POT1 gene expression using qPCR.

Corticosterone: We extracted hormone from plasma using ether extractions and quantified CORT levels using an enzyme immunoasssay kit (Cayman #501320). 

Datasets: The "FemaleRNA" excel sheet is used to ask 1) whether female POT1 gene expression, telomere length, and other variables predicts several metrics of quality, and 2) whether POT1 and telomere length predict her responses to injection with saline or LPS. The "ChickTelomereData" excel sheet is used to ask 1) how chick phenotypes respond to maternal injections and 2) whether chick phenotypes predict fledging success and recruitment into the breeding population.

Please see the "Notes" tab on each excel datasheet for more details about the columns/variables.

Because of the nature of field work, each variable of interest does have missing data for some individuals. That information (# missing per variable and other subsetting) can be found in the methods section of the published manuscript.