DOI: 10.5061/dryad.c866t1g8c
title: Artificial size selection experiment reveals telomere length dynamics and fitness consequences in a wild passerine

description: Telomere dynamics could underlie life-history trade-offs among growth,
 size, and longevity, but our ability to quantify such processes in
 natural, unmanipulated populations is limited. We investigated how 4 years
 of artificial selection for either larger or smaller tarsus length, a
 proxy for body size, affected early-life telomere length (TL) and several
 components of fitness in two insular populations of wild house sparrows
 over a study period of 11 years. The artificial selection was expected to
 shift the populations away from their optimal body size and increase the
 phenotypic variance in body size. Artificial selection for larger
 individuals caused TL to decrease, but there was little evidence that TL
 increased when selecting for smaller individuals. There was a negative
 correlation between nestling TL and tarsus length under both selection
 regimes. Males had longer telomeres than females and there was a negative
 effect of harsh weather on TL. We then investigated whether changes in TL
 might underpin fitness effects due to the deviation from the optimal body
 size. Mortality analyses indicated disruptive selection on TL because both
 short and long early-life telomeres tended to be associated with the
 lowest mortality rates. In addition, there was a tendency for a negative
 association between TL 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 the wild may be
 associated with changes in TL during growth, which is known to be linked
 to longevity in some bird species.
description: Methods are detailed in the main text and in Appendix S1.
description: TL: Mean relative erythrocyte telomere length (TL) was measured
 using the qPCR method (Cawthon, 2002). tarsus:
 Tarsometatarsus ("tarsus") length was measured using calipers to
 the nearest 0.01 mm. Because tarsus length increases with nestling age, we
 estimated standardized tarsus length ("tarsus (age-corrected)")
 as the residuals of a multiple linear regression of tarsus length on age
 (in days) and age squared (i.e. a quadratic model) separately for each
 sex. The standardizations were made for each population separately such
 that we did not have to assume equal growth trajectories between
 treatments. "Adult tarsus" is the uncorrected tarsus length of
 the recaptured full-grown juvenile or adult individual.
 age: Number of days since hatching. sex:
 1=male, 2=female brood size: Number of chicks in the
 nest at the time of sampling. island_ID:
 60=<i>high</i> (Leka) or 61=<i>low</i>
 (Vega) selection regime. 
 brood_ID: Unique brood (clutch) identification number. selection_category: Refer to: <i>Selected </i>(1): Both parents had been subject to the selection regime, i.e. captured during a winter selection event and allowed to stay in the population. <i>Intermediate </i>(0.5): one parent had been subject to artificial selection. <i>Unselected </i>(0):<i> </i>No parents had been artificially selected (i.e. accidentally not captured during any winter selection event) and these individuals are therefore the unselected controls. NAO_30: The daily North Atlantic Oscillation (NAO) index (retrieved from the National Oceanic and Atmospheric Administration (NOAA), 2018) was averaged over a 30-day period prior to blood sampling ("NAO_30"). LRS: Total number of recruits produced (lifetime reproductive success). lifespan: Years between hatching and last observation. NA: Missing values.