Abstract

Although conflict is often adaptive and necessary to secure limited resources, it is also frequently a costly endeavor. Signals that reliably communicate competitive ability are commonly employed by animals to reduce conflict costs. Both male and female signals have the capacity to serve as honest indicators of competitive ability, but the extent to which this occurs in females has received relatively limited attention. We studied how natural feather coloration and experimentally manipulated plumage ornamentation in female white-shouldered fairywrens (Malurus alboscapulatus moretoni) relates to their aggressive behavior. These fairywrens are a useful study system in that female, but not male coloration varies throughout New Guinea. We tested behavioral responses to simulated rivals both prior to and after plumage manipulation via two distinct behavioral assays: simulated territorial intrusions (where both sexes jointly respond to rival intruders) and mirror image simulation (where females are isolated from their mate). Plumage manipulation treatments had no measurable impact on female aggression during mirror image simulation tests, though aggression did decrease over the course of multiple assays. Similarly, using simulated territorial intrusion assays, we found no difference in female aggression with respect to both natural coloration and manipulation treatment. Finally, our correlative analysis of natural feather color also revealed no detectable relationship. These findings suggest that female white scapular coloration is unlikely to function as a signal of competitive ability in this tropical species with derived female ornamentation and we discuss possible alternative explanations.

Significance statement

Like their showy male counterparts, female animals may use plumage-based signals to mediate aggressive encounters. Determining if and how signals used in female-female competition may mitigate the costs of agonistic encounters is particularly important, as it is thought to be a key driver of female signal evolution. We used a repeated-measures design and two distinct behavioral assays to explore how both manipulated and natural feather coloration relate to aggression in female white-shouldered fairywrens of Papua New Guinea – a species with female, but not male, plumage polymorphisms. We were unable to detect any differences in aggression with respect to female plumage coloration despite two distinct behavioral assays that mimic distinct social contexts, suggesting that female plumage coloration may function in other contexts or lack a modern signaling function altogether in this system.

中文翻译：

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雌性装饰不能预测热带鸣禽的攻击性

摘要

虽然冲突通常是适应性的，并且是确保有限资源所必需的，但它也经常是一项代价高昂的努力。动物通常使用可靠地传达竞争能力的信号来降低冲突成本。男性和女性信号都有能力作为竞争能力的诚实指标，但这种情况发生在女性身上的程度受到的关注相对有限。我们研究了雌性白肩仙女 ( Malurus alboscapulatus moretoni) 与他们的攻击性行为有关。这些仙女鹪鹩是该女性的一个有用的研究系统，但在整个新几内亚，雄性的颜色并没有变化。我们通过两种不同的行为分析测试了在羽毛操作之前和之后对模拟对手的行为反应：模拟领土入侵（两性共同对竞争对手的入侵者做出反应）和镜像模拟（雌性与配偶隔离）。在镜像模拟测试期间，羽毛操作处理对女性攻击性没有可测量的影响，尽管攻击性在多次检测过程中确实减少了。同样，使用模拟领土入侵分析，我们发现女性在自然着色和操纵处理方面的攻击性没有差异。最后，我们对天然羽毛颜色的相关分析也没有发现任何可检测的关系。这些发现表明，雌性白色肩胛骨颜色不太可能在这种具有衍生雌性装饰的热带物种中作为竞争能力的信号，我们讨论了可能的替代解释。

意义陈述

与艳丽的雄性动物一样，雌性动物可能会使用基于羽毛的信号来调解攻击性的遭遇。确定女性与女性竞争中使用的信号是否以及如何降低竞争性遭遇的成本尤为重要，因为它被认为是女性信号进化的关键驱动力。我们使用重复测量设计和两种不同的行为分析来探索操纵和自然羽毛颜色如何与巴布亚新几内亚的雌性白肩仙女的攻击性相关 - 一种具有雌性但不是雄性羽毛多态性的物种。尽管有两种不同的行为分析模拟了不同的社会背景，但我们无法检测到对雌性羽毛颜色的攻击性的任何差异，