Maternal stress promotes offspring growth without oxidative costs in wild red squirrels

Elevations in glucocorticoid levels (GCs) in breeding females (often called maternal stress) may induce adaptive shifts in offspring life histories. Offspring produced by mothers with elevated GCs may be better prepared to face harsh environments where a faster pace of life is beneficial. We examined how experimentally elevated GCs in pregnant or lactating North American red squirrels ( Tamiasciurus hudsonicus ) affected offspring growth in body mass, structural (skeletal) size, oxidative stress levels (balance of two antioxidants and one measure of oxidative protein damage) in three different tissues (blood, heart, liver), and liver telomere lengths. We predicted that offspring from mothers treated with GCs would grow faster but would also have higher levels of oxidative stress and shorter telomeres, which may predict reduced longevity. Offspring from mothers treated with GCs during pregnancy grew (in body mass) 17% faster than those from controls, whereas offspring from mothers treated with GCs during lactation grew 34.8% slower than those from controls. Treating mothers with GCs during pregnancy or lactation did not alter the oxidative stress levels or telomere lengths of their offspring, and fast-growing offspring did not have higher oxidative stress levels or shorter telomere lengths. Our results indicate that elevations in maternal GCs may induce plasticity in offspring growth without oxidative costs to the offspring that might result in a shortened lifespan.