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.

由于鸟类的孵卵行为需承担高昂的能量成本，亲鸟常会在孵卵投入与自身维持之间进行权衡。该权衡可表现为降低孵卵温度，但此举会给雏鸟带来高昂的躯体代价。目前学界对这类代价制约个体适合度的程度仍缺乏深入认知。我们采用三种具备生态学意义的温度对野生蓝山雀的窝卵进行孵育处理，随后记录了幼鸟的越冬存活率以及至繁殖季的存活率。来自最低温度处理组（35.0℃）的出飞幼鸟存活率低于其他处理组幼鸟，但各处理组间的越冬存活个体占比与繁殖季存活个体占比均无显著差异。不过，来自低、中孵卵温度处理组的个体，其两个季节的存活概率均随出飞时体重的增加而升高；而来自高温处理组的个体，其存活概率却随出飞体重的增加而降低。中温度处理组的雏鸟发育为成体后体重更高，较低、高温处理组的存活个体重7%。由此可见，较高的孵卵温度在短期内或具有益处，但从长期来看，胚胎发育加速所带来的代价可能与发育时长延长的代价不相上下。这种发育更快的隐性后果，或许会维持针对平均孵卵温度的自然选择压力。