"Does Egg Viability Constrain the Onset of Incubation in Birds? An Experimental Analysis using a Tropical Climate Gradient"

鸟类在脊椎动物中是独一无二的，因为它们可以通过决定何时开始孵蛋来控制蛋的孵化间隔。然而，许多鸟类父母选择一种孵化策略，使它们的蛋不同步孵化，这往往导致幼雏的死亡。在孵化之前，研究人员很少考虑气温如何影响卵的存活（卵生存力假说）。卵子在24摄氏度以下不会发育，必须由父母将其加热到36摄氏度，以确保正常发育。胚胎发育异常导致死亡是由于卵子长期暴露在中等温度（27度-35度）下造成的。这项为期3年的研究采用了波多黎各一座热带山脉斜坡上的自然气候梯度，用珍珠眼Thrasher （Margarops fuscatus）的卵来测试卵活力假说，这种物种在山上的洞穴（和巢箱）中筑巢。PI将把未孵化的蛋上下移动到山上，让它们暴露在不同的温度环境中，并测量它们随后的孵化成功率。PI还将把脱粒机卵放在孵化器中，使它们暴露在与山区温度变化平行的受控温度变化中。最后，PI将使用摄像机和温度记录仪来检查撞击者在这个梯度上是否会改变孵化的开始时间。这将是第一个通过实验将鸟蛋暴露在一组关键的温度下，利用自然热机制来检查影响鸟蛋孵化成功的因素的研究。未孵蛋孵化成功率的下降可能有助于理解为什么热带鸟类比温带鸟类产卵少，以及全球变暖可能对它们的蛋孵化成功率产生什么影响。

Birds are unique among vertebrates because they can control the hatching intervals of their eggs by determining when to start incubating them. However, many avian parents choose an incubation strategy that causes their eggs to hatch asynchronously, which often leads to the death of younger chicks. Researchers have rarely considered how air temperature affects the survival of eggs before they are incubated (the Egg Viability Hypothesis). Eggs do not develop below 24 degrees C and must be warmed by a parent to 36 degrees to ensure proper development. Abnormal development of embryos leading to death is caused by prolonged exposure of eggs to intermediate temperatures (27 degrees-35 degreesC).This 3-year study employs a natural climate gradient along the slope of a tropical mountain in Puerto Rico to test the Egg Viability Hypothesis using eggs of the Pearly-eyed Thrasher (Margarops fuscatus), a species that nests in cavities (and nest boxes) throughout the mountain. The PI will move unincubated eggs up and down the mountain to expose them to different temperature regimes, and measure their subsequent hatching success. The PI will also place thrasher eggs in incubators to expose them to controlled changes in temperature that parallel temperature changes along the mountain. Finally, the PI will use video cameras and temperature recorders to examine whether thrashers vary the onset of incubation across this gradient. This will be the first study to examine the factors that affect the hatching success of bird eggs by experimentally exposing them to a critical set of temperatures using a natural thermal regime. A decline in the hatching success of unincubated eggs may have implications for understanding why tropical birds lay few eggs than temperate counterparts and what might happen to the hatching success of their eggs from global warming.