Egg Testosterone Differentially Affects Telomere Length in Somatic Tissues of Yellow-Legged Gull Embryos

Maternal decisions on egg composition have major consequences for offspring. Maternal egg androgens have diverse, often contrasting, effects depending on offspring trait and life stage, suggesting that mothers face trade-offs in egg hormone transfer. However, the effect of egg androgens on embryonic telomere length, which is a major trait potentially affecting performance, has been never investigated. We administered a physiological dose of testosterone (T) to yellow-legged gull (Larus michahellis) eggs and found that, compared to controls, telomere length shortly before hatching was reduced in the liver but unaffected in the brain, heart, and pectoralis muscle. Telomere length varied across somatic tissues, and, independent of egg treatment, it was not correlated between them, suggesting independent telomere dynamics. Thus, we showed for the first time that increased egg T can increase telomere shortening in the embryo and that maternal T allocation strategies may evolve also in response to such effect. Moreover, contrary to observations in adult birds, at the embryonic stage telomere length in one somatic tissue may not reflect telomere length in other body districts.