Environmental effects and life-history variation in birds

父母在塑造他们的后代方面起着至关重要的作用。母亲尤其可能通过产前转移激素或抗体和/或通过产后护理来影响后代。当母亲经历有压力的环境时，后代可能会表现出与没有压力的母亲的后代不同的生理和行为。传统上，这被视为不良养育环境的非适应性后果。一种新的观点是，母亲们实际上正在调整她们的后代，以更好地应对随后的环境挑战。出生前和出生后线索在塑造后代方面的相对重要性已经在实验室动物中进行了研究，但直到最近才在野外进行。 我提出的研究的主要目标是使用野生鸟类来测试出生前和出生后的母体线索是否会以一种适应性的方式改变后代的生理和行为。在我提议的研究中，我和我的学生将回答三个一般性问题：(1)产前激素信号在塑造后代特征方面扮演什么角色，它们是否会提高存活率？(2)母亲是否会在不同的温度下孵化卵子，以调整后代的特征？(3)压力是否会影响母亲将抗体转移给子女的能力，以及她是否会调整对环境中病原体数量的反应？ 为了测试问题1和2，我们将研究环嘴鸥。我们建议在干扰程度不同的海鸥群体区域之间交换卵子。“错配”雏鸡将在产前得到母体提示的某种程度的干扰(通过它们的卵子)，但将在不同的干扰级别中饲养；“匹配”的雏鸟将在产蛋所在的殖民地的同一地区饲养(以及相同级别的干扰)。如果产前提示导致小鸡适应能力的调整，我们预测来自“不匹配”环境的小鸡的质量将低于来自“匹配”环境的小鸡，存活率也会低于来自“匹配”环境的小鸡。“错配”小鸡的母亲第二年的回报率会更低。我们还将实验性地操纵鸡蛋皮质酮水平(母体压力的荷尔蒙线索)，将圈养的雏鸟暴露在不同形式的压力下，并在下一年测量它们的行为和生理。 从理论上讲，母亲也可以使用卵子孵化温度作为一种机制来调整她们的后代(问题2)。为了测试这一点，我们将远程监测实验中压力过大/非压力过大的母亲的巢温度。我们预测，压力过大的母亲的卵子将经历更大的温度波动。如果中断的孵化行为是母亲塑造后代的一种机制，我们预测，与来自未受干扰的巢中的雏鸟相比，来自受干扰巢中的雏鸟对压力的反应将变得迟钝。这是如何发生的尚不清楚，但我们将测试胚胎是否通过产生自己的荷尔蒙信号来发挥作用。 母亲可以将抗体转移到卵子上，有可能偏袒一个性别而不是另一个。母亲也可以根据环境中病原体的数量来分配抗体。使用树燕子，我们将比较温带种群和亚热带种群的卵的抗体水平，并测试雏鸟对免疫挑战的反应能力是否不同(问题3)。我们预测，当受到压力时，温带雌性将比亚热带雌性(那里有更多病原体)传递更少的抗体，这对温带后代会产生负面影响。如果母亲的压力限制了女性产前转移抗体的能力，可能会对经历环境退化和新出现疾病威胁的人群产生负面后果。

Parents play a critical role in shaping their offspring. Mothers in particular may influence offspring via prenatal transfer of hormones or antibodies and/or via postnatal care. When mothers experience stressful environments, offspring may display differing physiologies and behaviours from offspring of non-stressed mothers. Traditionally, this has been viewed as a non-adaptive consequence of a poor rearing environment. An emerging perspective is that mothers are in fact adjusting their offspring to better cope with subsequent environmental challenges. The relative importance of pre and postnatal cues in shaping offspring has been studied in laboratory animals, but only recently in the wild. The major goal of my proposed research is to use wild birds to test whether pre- and postnatal maternal cues change offspring physiology and behaviour in an adaptive way. In my proposed research, my students and I will address three general questions: (1) What is the role of prenatal hormonal cues in shaping offspring characteristics, and do they increase survival? (2) Do mothers incubate their eggs at different temperatures to adjust offspring characteristics? (3) Does stress impact a mother’s ability to transfer antibodies to her offspring, and does she adjust her response to the number of pathogens in the environment? To test questions 1 and 2, we will study ring-billed gulls. We propose to swap eggs between regions of a gull colony that differ in levels of disturbance. “Mismatched” chicks will receive prenatal maternal cues of one level of disturbance (via their egg), but will be raised in a different level of disturbance; “Matched” chicks will be reared in the same area of the colony in which their eggs were laid (and same level of disturbance). If prenatal cues result in adaptive adjustments in the chicks, we predict chicks from “mismatched” environments will be of lower quality and have lower survival than chicks from “matched” environments. The mothers of “mismatched” chicks will have lower return rates the following year. We will also experimentally manipulate egg corticosterone levels (a hormonal cue of maternal stress), expose captive chicks to differing forms of stress, and measure their behaviour and physiology the following year. Theoretically, mothers may also use egg incubation temperature as a mechanism to adjust their offspring (Question 2). To test this, we will remotely monitor nest temperatures of experimentally stressed/non-stressed mothers. We predict that eggs of stressed mothers will experience greater fluctuations in temperature. If disrupted incubation behaviour is a mechanism for mothers to shape their offspring, we predict chicks from disturbed nests will show a blunted response to stress when compared with chicks from non-disturbed nests. How this occurs is not known, but we will test whether embryos play a role via producing their own hormonal cues of stress. Mothers can transfer antibodies to their eggs, with potential to show favouritism to one sex over the other. Mothers may also allocate antibodies according to the number of pathogens in the environment. Using tree swallows, we will compare antibody levels of eggs from temperate populations with subtropical populations, and test whether nestlings differ in their ability to respond to an immune challenge (Question 3). We predict that when stressed, temperate females will transfer fewer antibodies than will sub-tropical females (where there are more pathogens), with negative consequences for temperate offspring. If maternal stress limits a female’s ability to transfer antibodies prenatally, there may be negative consequences for populations that experience combinations of environmental degradation and the threat of emerging diseases.