Benefits of an anti-parasite treatment are influenced by within-brood size variation in Tree Swallows (Tachycineta bicolor)

In all animals, susceptibility to parasites can differ among individuals. Young, nest-bound birds are exposed to a diversity of nest-dwelling ectoparasites that typically feed on their blood. Within broods, hatching asynchrony creates size hierarchies that result in morphological and physiological variation among nest mates, and susceptibility to parasites also may vary predictably with this size hierarchy. Our objective was to use a broad-spectrum, anti-parasite drug, ivermectin (IVM), to treat individual nestling Tree Swallows (Tachycineta bicolor) and assess how nestling susceptibility to parasites varied both within and among broods. Broods were either assigned to an IVM group, where half of the nestlings in a brood received IVM injections and half received control injections of pure sesame oil, or to a control group, where all nestlings received oil injections. We found that the IVM treatment reduced parasite loads for broods as a whole, thereby benefiting all nestlings in IVM broo...

在所有动物类群中，个体间的寄生虫易感性存在差异。尚留巢的幼鸟会接触到多种以血液为食的巢栖外寄生物。在同一窝雏鸟中，孵化异步性会形成体型等级，导致同巢幼鸟间出现形态与生理差异，而寄生虫易感性也会随该体型等级呈现可预测的变化。本研究旨在利用广谱抗寄生虫药物伊维菌素（ivermectin, IVM）对单只树燕（Tachycineta bicolor）雏鸟进行处理，并评估雏鸟的寄生虫易感性在窝内及窝间的变化规律。研究将各窝雏鸟分为两组：伊维菌素组（窝内半数雏鸟接受伊维菌素注射，另一半接受纯芝麻油对照注射），以及纯对照组（所有雏鸟均接受芝麻油注射）。我们发现，伊维菌素处理可整体降低整窝雏鸟的寄生虫负荷，从而使伊维菌素组窝内的所有雏鸟均获益...