DataSheet2_A prenatal acoustic signal of heat reduces a biomarker of chronic stress at adulthood across seasons.csv

During development, phenotype can be adaptively modulated by environmental conditions, sometimes in the long-term. However, with weather variability increasing under climate change, the potential for maladaptive long-term responses to environmental variations may increase. In the arid-adapted zebra finch, parents emit “heat-calls” when experiencing heat during incubation, which adaptively affects offspring growth in the heat, and adult heat tolerance. This suggests that heat-call exposure may adjust individual phenotype to hot conditions, potentially compromising individual sensitivity to cool weather conditions. To test this hypothesis, we manipulated individual prenatal acoustic and postnatal thermal experiences during development, and sought to assess subsequent chronic responses to thermal fluctuations at adulthood. We thus measured heterophil to lymphocyte (H/L) ratios in adults, when held in outdoor aviaries during two summers and two winters. We found that birds exposed to heat-calls as embryos, had consistently lower H/L ratios than controls at adulthood, indicative of lower chronic stress, irrespective of the season. Nonetheless, in all birds, the H/L ratio did vary with short-term weather fluctuations (2, 5 or 7 days), increasing at more extreme (low and high) air temperatures. In addition, the H/L ratio was higher in males than females. Overall, while H/L ratio may reflect how individuals were being impacted by temperature, heat-call exposed individuals did not show a stronger chronic response in winter, and instead appeared more resilient to thermal variability than control individuals. Our findings therefore suggest that heat-call exposure did not compromise individual sensitivity to low temperatures at adulthood. Our study also reveals that prenatal sound can lead to long-term differences in individual physiology or quality/condition, as reflected by H/L ratios, which are consistent with previously-demonstrated reproductive fitness differences.

在开发过程中，表型可能受到环境条件的适应性调节，有时这种调节作用会持续较长时间。然而，随着气候变化导致的天气变率增加，对环境变化产生不适应性长期响应的可能性也随之上升。在适应干旱环境的斑马雀中，当父母在孵化期间经历高温时，会发出‘热叫声’，这种叫声能够适应性影响后代在高温下的生长以及成年后的耐热性。这表明，热叫声的暴露可能调整个体的表型以适应高温条件，从而可能损害个体对凉爽天气条件的敏感性。为了验证这一假设，我们在发育过程中操纵了个体在产前和产后的声学及热体验，并试图评估成年后对温度波动的慢性反应。因此，我们在两个夏季和两个冬季将成年斑马雀置于户外鸟舍中，测量了异嗜细胞与淋巴细胞（H/L）的比例。我们发现，作为胚胎暴露于热叫声的鸟类，其成年后的H/L比例比对照组显著降低，这表明长期压力较低，不受季节影响。尽管如此，在所有鸟类中，H/L比例都会随着短期天气波动（2、5或7天）而变化，在极端的（低温和高温）空气温度下增加。此外，雄性的H/L比例高于雌性。总体而言，虽然H/L比例可能反映了个体受到温度影响的方式，但暴露于热叫声的个体在冬季并未表现出更强的慢性反应，反而似乎比对照组更能抵抗温度变化。因此，我们的研究结果表明，热叫声的暴露并没有损害成年个体对低温的敏感性。此外，我们的研究还揭示了产前声音可以导致个体生理或质量/条件方面的长期差异，这反映在H/L比例上，这与先前观察到的繁殖力差异一致。