Disseration Research: Ecological and Hormonal Bases of Paternal Care in the Chestnut-collared Longspur, Calcarius ornatus

雄鸟比其他脊椎动物的雄鸟更多地参与父母的照顾。因此，鸟类代表了一个非同寻常的模型，可以解开影响照顾幼崽的各种因素。当繁殖开始时，雄性经历了荷尔蒙睾酮(T)的上升，而在幼崽孵化时，睾酮(T)下降。这种模式可能代表了T水平和父亲关爱的表达之间的权衡：从实验上看，T水平高与减少父亲关爱有关，有利于增强性行为。在板栗领长刺(CCLO)中，实验中增加的T促进了卵孵化前的性行为，但令人惊讶的是，并没有减少对雏鸟的照顾。这项研究将验证这样一种假设，即在父母阶段发生这种对T不敏感的异常情况，是因为雄性对雏鸟的生存至关重要。通过操纵环境和荷尔蒙变量，这项研究将确定(1)雄性护理是否必要，(2)环境是否推动雄性护理，以及(3)T升高是否影响CCLO中的巢防御。雄性照顾，虽然在自然界中一般很少见，但在鸟类中很普遍。然而，父亲的照顾是由环境因素还是由内在因素驱动的，目前尚不清楚。这项研究将有助于揭示荷尔蒙和环境线索在表达父亲关怀方面的相对作用。确定环境因素在T和父系照顾之间的明显权衡中的作用特别重要，因为它可以应用于额外的系统，在这些系统中，父系照顾对幼崽的生存至关重要。

Male birds participate in parental care more than males of any other vertebrate group. Thus, birds represent an extraordinary model to untangle the various factors that affect care of young. When breeding begins, males experience a rise in the hormone testosterone (T) that declines by the time young hatch. This pattern may represent a trade-off between T levels and expression of paternal care: experimentally, high levels of T are associated with reduced paternal care in favor of enhanced sexual behavior. In chestnut-collared longspurs (CCLO), experimentally increased T enhances sexual behavior before eggs hatch, but surprisingly, does not reduce care of nestlings. This study will test the hypothesis that this unusual insensitivity to T during the parental phase occurs because males are critical for nestling survival. By manipulating environmental and hormonal variables, this study will determine (1) if male care is essential, (2) if the environment drives male care, and (3) if elevated T affects nest defense in CCLO. Male care, though generally rare in nature, is prevalent in birds. Whether paternal care is driven by environmental factors or by internal cues, however, is unknown. This study will help to unravel the relative roles of hormones and environmental cues on the expression of paternal care. Determining the role of environmental factors in the apparent trade-off between T and paternal care is particularly important, because it can be applied to additional systems in which paternal care is critical for survival of young.