Department of Psychology, University of Michigan, Ann Arbor, MI48109-1043, USA.
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada, T6G 2E9.
J Exp Biol. 2021 May 15;224(10). doi: 10.1242/jeb.236620. Epub 2021 May 25.
As a response to environmental cues, maternal glucocorticoids (GCs) may trigger adaptive developmental plasticity in the physiology and behavior of offspring. In North American red squirrels (Tamiasciurus hudsonicus), mothers exhibit increased GCs when conspecific density is elevated, and selection favors more aggressive and perhaps more active mothers under these conditions. We tested the hypothesis that elevated maternal GCs cause shifts in offspring behavior that may prepare them for high-density conditions. We experimentally elevated maternal GCs during gestation or early lactation. We measured two behavioral traits (activity and aggression) in weaned offspring using standardized behavioral assays. Because maternal GCs may influence offspring hypothalamic-pituitary-adrenal (HPA) axis dynamics, which may in turn affect behavior, we also measured the impact of our treatments on offspring HPA axis dynamics (adrenal reactivity and negative feedback), and the association between offspring HPA axis dynamics and behavior. Increased maternal GCs during lactation, but not gestation, slightly elevated activity levels in offspring. Offspring aggression and adrenal reactivity did not differ between treatment groups. Male, but not female, offspring from mothers treated with GCs during pregnancy exhibited stronger negative feedback compared with those from control mothers, but there were no differences in negative feedback between lactation treatment groups. Offspring with higher adrenal reactivity from mothers treated during pregnancy (both controls and GC-treated) exhibited lower aggression and activity. These results suggest that maternal GCs during gestation or early lactation alone may not be a sufficient cue to produce substantial changes in behavioral and physiological stress responses in offspring in natural populations.
作为对环境线索的反应，母体糖皮质激素（GCs）可能会引发后代生理和行为的适应性发育可塑性。在北美红松鼠（Tamiasciurus hudsonicus）中，当同种密度增加时，母亲的 GCs 会增加，而在这些条件下，选择有利于更具攻击性和更活跃的母亲。我们检验了这样一个假设，即母体 GCs 的升高导致了后代行为的转变，这可能使它们为高密度条件做好准备。我们在妊娠期或哺乳期早期通过实验升高了母体 GCs。我们使用标准化行为测定法在断奶后代中测量了两种行为特征（活动和攻击性）。因为母体 GCs 可能影响后代下丘脑-垂体-肾上腺（HPA）轴的动态，这可能反过来影响行为，所以我们还测量了我们的处理对后代 HPA 轴动态（肾上腺反应性和负反馈）的影响，以及后代 HPA 轴动态与行为之间的关联。哺乳期母体 GCs 的增加，而不是妊娠期，略微提高了后代的活动水平。各组之间的后代攻击性和肾上腺反应性没有差异。与对照组母亲相比，怀孕期间接受 GCs 治疗的雄性后代的负反馈明显强于对照组，但哺乳期处理组之间的负反馈没有差异。来自怀孕期间接受治疗的母亲（对照组和 GCs 处理组）的具有较高肾上腺反应性的后代表现出较低的攻击性和活动水平。这些结果表明，在自然种群中，妊娠期或哺乳期早期单独的母体 GCs 可能不足以引起后代行为和生理应激反应的实质性变化。
