Long-lasting consequences of elevated yolk testosterone for metabolism in the zebra finch

Resting metabolic rate is a common way of quantifying the cost of living in endothermic animals. The trait often makes up a substantial part of an animal's energy budget and can also be related to sustainable peak work rate as well as to daily energy expenditure. Studies have shown that metabolic rates are often heritable, but much of the variation seems to be caused by other factors (e.g., environmental and maternal effects). In a previous study, in ovo exposure to increased levels of testosterone induced metabolic costs early in life. It is, however, unknown whether in ovo androgens also have long-term effects on individual metabolic rates. In this study, we show that experimentally increased levels of in ovo testosterone in zebra finches (Taeniopygia guttata) result in a 7% higher resting metabolic rate when they are adults. This shows that maternally transferred hormones can induce long-term effects on metabolic demands and potentially influence variation in life-history strategies among offspring. Variation in maternal hormone transfer may also explain some of the large interindividual variation observed in metabolic rates.