Henderson L J, Evans N P, Heidinger B J, Herborn K A, Arnold K E
Centre for Behaviour and Evolution, IoN, Newcastle University, Henry Wellcome Building, Framlington Place, Newcastle NE2 4HH, UK.
Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, The University of Glasgow, Glasgow G12 8QQ, UK.
R Soc Open Sci. 2017 Oct 18;4(10):170875. doi: 10.1098/rsos.170875. eCollection 2017 Oct.
Glucocorticoids, including corticosterone (CORT), have been suggested to provide a physiological link between ecological conditions and fitness. Specifically, CORT, which is elevated in response to harsh conditions, is predicted to be correlated with reduced fitness. Yet, empirical studies show that CORT can be non-significantly, positively and negatively linked with fitness. Divergent environmental conditions between years or study systems may influence whether CORT is linked to fitness. To test this, we monitored free-living blue tits () during breeding over 3 years. We quantified foraging conditions during brood rearing, and examined whether they were correlated with parental baseline CORT and reproductive success. We then tested whether CORT predicted fitness. Elevated parental CORT was associated with lower temperatures, greater rainfall and lower territory-scale oak density. Whereas asynchrony with the caterpillar food peak was correlated with reduced nestling mass and fledging success, but not parental CORT. Only low temperatures were associated with both reduced nestling mass and elevated parental CORT. Despite this, parents with elevated CORT had lighter offspring in all years. Contrarily, in 2009 parental CORT was positively correlated with the number fledged. The absence of a direct link between the foraging conditions that reduce nestling quality and elevate parental CORT suggests that parental CORT may provide a holistic measure of conditions where parents are working harder to meet the demands of developing young. As the positive correlation between parental CORT and fledging success differed between years, this suggests that contrasting conditions between years can influence correlations between parental CORT and fitness. Ultimately, as CORT concentrations are intrinsically variable and linked to the prevalent conditions, studies that incorporate environmental harshness will improve our understanding of evolutionary endocrinology.
包括皮质酮（CORT）在内的糖皮质激素被认为在生态条件与适应性之间提供了一种生理联系。具体而言，CORT会因恶劣条件而升高，预计它与适应性降低相关。然而，实证研究表明，CORT与适应性之间可能不存在显著关联，也可能呈正相关或负相关。年份或研究系统之间不同的环境条件可能会影响CORT是否与适应性相关。为了验证这一点，我们在三年的繁殖期内对自由生活的蓝山雀（ ）进行了监测。我们量化了育雏期间的觅食条件，并研究了它们是否与亲代基线CORT和繁殖成功率相关。然后我们测试了CORT是否能预测适应性。亲代CORT升高与较低温度、较多降雨和领地尺度上较低的橡树密度有关。而与毛虫食物高峰不同步与雏鸟体重减轻和出飞成功率降低相关，但与亲代CORT无关。只有低温与雏鸟体重减轻和亲代CORT升高都有关。尽管如此，CORT升高的亲代在所有年份的后代都较轻。相反，在2009年，亲代CORT与出飞数量呈正相关。降低雏鸟质量并提高亲代CORT的觅食条件之间不存在直接联系，这表明亲代CORT可能提供了一种综合衡量条件的指标，在此条件下亲代需要更加努力地满足发育中雏鸟的需求。由于亲代CORT与出飞成功率之间的正相关在不同年份有所不同，这表明年份之间不同的条件会影响亲代CORT与适应性之间的相关性。最终，由于CORT浓度本质上是可变的且与普遍条件相关，纳入环境恶劣程度的研究将增进我们对进化内分泌学的理解。
