Data from: Long-term consequences of high incubation temperature in a wild bird population

Because incubation by birds is energetically costly, parents frequently trade off investment in incubation against self-maintenance. This can be manifested by a reduction in incubation temperature, which comes at high somatic costs for nestlings. The extent to which these costs constrain fitness is poorly understood. We incubated wild blue tit clutches at three biologically relevant temperatures and subsequently recorded winter survival and survival to the breeding season. Fledglings from the coldest treatment (35.0°C) survived less well than other fledglings, but the proportion of winter and breeding survivors did not differ significantly between treatments. However, survival probability in both seasons increased with body mass at fledging in birds from low and mid incubation temperatures, but decreased with fledging body mass in the high-temperature treatment. Mid-temperature nestlings were heavier as adults, weighing 7% more than low- and high-temperature survivors. Thus, high incubation temperature can be beneficial in the short term, but costs of accelerated embryonic development may equal those of protracted development in the long term. Such hidden consequences of faster development could maintain natural selection for average incubation temperature.

鸟类的孵卵行为会消耗大量能量，因此亲鸟通常会在孵卵投入与自身能量维持之间进行权衡取舍。这可表现为孵卵温度的降低，而这会给雏鸟带来高昂的身体发育代价。目前学界对这类代价对雏鸟适合度的制约程度仍知之甚少。我们将野生青山雀（Blue Tit）的卵簇置于三种符合生物学意义的温度下进行孵育，随后记录了雏鸟的冬季存活率以及繁殖季存活率。来自最低温度组（35.0℃）的雏鸟存活率低于其他温度组的雏鸟，但各温度组的冬季存活个体占比与繁殖季存活个体占比均无显著差异。不过，对于低、中等孵卵温度组的个体而言，两个季节的存活概率均随其出飞时的体重增加而升高；而高温组个体的存活概率则随出飞体重增加而降低。中等温度组的雏鸟在成年后体重更高，比低、高温组的存活个体重7%。由此可见，高孵卵温度在短期内可能具有益处，但从长期来看，胚胎发育加速所带来的代价可能与发育周期延长的代价不相上下。这种发育更快所带来的隐性后果，可能会维持针对平均孵卵温度的自然选择。