Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, P,O, Box 11103, 9700, CC Groningen, The Netherlands.
Front Zool. 2013 Dec 17;10(1):77. doi: 10.1186/1742-9994-10-77.
Life-history theory predicts that organisms trade off survival against reproduction. However, the time scales on which various consequences become evident and the physiology mediating the cost of reproduction remain poorly understood. Yet, explaining not only which mechanisms mediate this trade-off, but also how fast or slow the mechanisms act, is crucial for an improved understanding of life-history evolution. We investigated three time scales on which an experimental increase in body mass could affect this trade-off: within broods, within season and between years. We handicapped adult skylarks (Alauda arvensis) by attaching extra weight during first broods to both adults of a pair. We measured body mass, immune function and return rates in these birds. We also measured nest success, feeding rates, diet composition, nestling size, nestling immune function and recruitment rates.
When nestlings of first broods fledged, parent body condition had not changed, but experimental birds experienced higher nest failure. Depending on the year, immune parameters of nestlings from experimental parents were either higher or lower than of control nestlings. Later, when parents were feeding their second brood, the balance between self-maintenance and nest success had shifted. Control and experimental adults differed in immune function, while mass and immune function of their nestlings did not differ. Although weights were removed after breeding, immune measurements during the second brood had the capacity to predict return rates to the next breeding season. Among birds that returned the next year, body condition and reproductive performance a year after the experiment did not differ between treatment groups.
We conclude that the balance between current reproduction and survival shifts from affecting nestlings to affecting parents as the reproductive season progresses. Furthermore, immune function is apparently one physiological mechanism involved in this trade-off. By unravelling a physiological mechanism underlying the trade-offs between current and future reproduction and by demonstrating the different time scales on which it acts, our study represents an important step in understanding a central theory of life-history evolution.
生活史理论预测生物在生存和繁殖之间进行权衡。然而，各种后果显现的时间尺度以及介导繁殖成本的生理学机制仍知之甚少。然而，不仅要解释介导这种权衡的机制是什么，还要解释这些机制的作用速度有多快或多慢，对于更好地理解生活史进化至关重要。我们研究了三个时间尺度，即在这三个时间尺度上，身体质量的增加会影响这种权衡：在育雏期内、在季节内和在年际间。我们通过在一对成鸟的第一窝雏鸟身上附加额外的重量来限制成年云雀（Alauda arvensis）的体重。我们测量了这些鸟的体重、免疫功能和归巢率。我们还测量了巢的成功率、喂养率、饮食组成、雏鸟大小、雏鸟免疫功能和招募率。
当第一窝雏鸟离巢时，亲体的身体状况没有改变，但实验鸟类的巢失败率更高。根据年份的不同，来自实验亲鸟的巢雏的免疫参数要么高于，要么低于对照巢雏。后来，当父母喂养第二窝雏鸟时，自我维持和巢成功之间的平衡发生了变化。对照和实验成鸟的免疫功能不同，而它们的巢雏的体重和免疫功能没有差异。虽然繁殖后去除了重量，但第二窝繁殖期间的免疫测量值有能力预测下一个繁殖季节的归巢率。在第二年返回的鸟类中，处理组之间在实验一年后的身体状况和繁殖表现没有差异。
我们的结论是，随着繁殖季节的进展，当前繁殖和生存之间的平衡从影响雏鸟转移到影响亲鸟。此外，免疫功能显然是这种权衡中的一个生理机制。通过揭示当前和未来繁殖之间权衡的生理机制，并证明其作用的不同时间尺度，我们的研究代表了理解生活史进化中心理论的重要一步。
