Variable parental responses to changes in offspring demand have implications for life history theory

Parental care, a component of reproductive effort, should evolve in response to its impact on both offspring and parent fitness. If so, manipulations in brood value should shift levels of care in predictable ways, provided that appropriate cues about the change in offspring value are altered. Prior brood size manipulations in birds have produced considerable variation in responses that have not been fully investigated. We conducted paired, short-term (2h) reductions and enlargements in brood size (+/- 2 nestlings) of house sparrows in each of 4 years. Parents at reduced broods shifted parental care downward in all four seasons. Parents experiencing increased broods responded significantly variably across years; in some they increased care, but in others they decreased care compared to control periods. Nestlings in both treatments gained less mass than during control sessions, with year producing variable effects in enlarged broods. We found evidence that parents experiencing reduced bro...

亲本抚育（Parental care）作为繁殖投入的组成部分，其演化应响应其对后代与亲本自身适合度的双重影响。若该假设成立，则当改变关于后代价值变化的恰当线索时，对窝雏价值的操控可使亲本抚育水平按照可预测的方式发生改变。此前针对鸟类的窝雏数量操控实验已得到差异显著的响应结果，但此类结果尚未得到充分研究。我们在4个年度中，对家麻雀的窝雏数量开展配对式短期（2小时）操控：分别增加或减少2只雏鸟。在窝雏数量减少的实验组中，亲本的抚育水平在全部4个年度均出现下降。而窝雏数量增加的实验组中，亲本的响应在各年度间存在显著差异：部分年度亲本提升了抚育投入，其余年度则相较于对照期降低了抚育水平。两种操控处理下的雏鸟体重增长均低于对照阶段，且在窝雏数量增加的组中，年度因素对体重增长存在可变影响。我们发现有证据表明，窝雏数量减少的亲本……