Telomere length data from a wild population of Seychelles Warblers on Cousin Island, 1995-2014

Blood samples (~25 μl) were collected and stored at room temperature in absolute ethanol. DNA was extracted using a DNeasy blood and tissue kit (Qiagen) according to the manufacturer’s instructions with modification of overnight lysis at 37 °C and a final DNA elution volume of 80 μl. DNA concentration and purity were quantified using a NanoDrop 8000 Spectrophotometer (ThermoScientific). The following thresholds were applied before samples were included for further analysis: (1) DNA concentration must be at least 15 ng/μl (based on a mean of three measurements), (2) the 260/280 absorbance ratio has to be between 1.8 and 2.0 for acceptable DNA purity, and (3) the 260/230 absorbance ratio must be higher than 1.8. DNA integrity was further validated by visualisation with ethidium bromide after electrophoresis on a 1.2% agarose gel, and all samples with evidence of DNA degradation were re-extracted or excluded. All DNA extractions that passed the above criteria were diluted to 3.3 ng/μl before telomere measurement. We used quantitative polymerase chain reaction to calculate a relative measure of telomere length that describes the amount of telomeric DNA in a sample relative to that of GAPDH, a constantly expressed reference gene.