Reduced telomere length in embryos exposed to predator cues.

It is often assumed that embryos are isolated from external influences, but recent studies indicate that environmental stressors during prenatal stages can exert long-term negative effects on fitness. A potential mechanism by which predation risk may lastingly shape life-history traits and phenotypes is via effects on telomeres. However, whether prenatal exposure to environmental stressors, such as cues of predator presence, affects postnatal telomere length has not hitherto been investigated. Using an experimental design in which we modified the exposure of yellow-legged gull () embryos to social cues of predator presence (i.e. alarm calls), we show that prenatally exposed chicks had shorter telomeres after hatching. As young birds with shorter telomere lengths have reduced fledging success, reproductive success and lifespan, the reduced telomere length in the exposed chicks is likely to have long-term fitness consequences. Moreover, our results provide a mechanistic link through which predators may negatively affect population dynamics.