Data from: Working with what you’ve got: unattractive males show greater mate-guarding effort in a duetting songbird

When mates are limited, individuals should allocate resources to mating tactics that maximize fitness. In species with extra-pair paternity (EPP), males can invest in mate guarding, or, alternatively, in seeking EPP. Males should optimize fitness by adjusting investment according to their attractiveness to females, such that attractive males seek EPP, and unattractive males guard mates. This theory has received little empirical testing, leaving our understanding of the evolution of mating tactics incomplete; it is unclear how a male’s relative attractiveness influences his tactics. We conducted observations and experiments on red-backed fairy-wrens (Malurus melanocephalus) to address this question. We found that older, more attractive (red-black) males sought EPP, whereas unattractive (brown) males invested in alternative tactics – physical and acoustic mate guarding. Younger red-black males used intermediate tactics. This suggests that males adopt mating tactics appropriate to their attributes. Males obtained similar reproductive success, suggesting these alternative tactics may maximize each male’s paternity gain. Though it is possible that the proximate mechanism of paternity gain is under either male, or female control, we establish that the many interconnected components of a male’s sexual phenotype influence the evolution of his decision-making rules, deepening our understanding of how mating tactics evolve under sexual selection.

当交配机会受限时，个体应将资源分配至可最大化自身适合度的交配策略中。在存在婚外父权（extra-pair paternity, EPP）的物种中，雄性可选择投资于配偶守护行为，或是转而寻求婚外父权。雄性应根据自身对雌性的吸引力调整资源投入，以优化适合度：对雌性更具吸引力的雄性会寻求婚外父权，而吸引力较弱的雄性则会采取配偶守护策略。该理论尚未得到充分的实证检验，导致我们对交配策略演化的理解仍存在缺口；目前尚不清楚雄性的相对吸引力如何影响其交配策略选择。为此，我们对红背细尾鹩莺（Malurus melanocephalus）开展了野外观察与控制实验，以解答这一科学问题。研究发现，年龄更大、羽色呈红黑色（更具吸引力）的雄性会寻求婚外父权，而羽色呈棕色（吸引力较弱）的雄性则会采取替代性策略——即物理配偶守护与声学配偶守护。年龄较轻的红黑色羽色雄性则采用介于两者之间的中间策略。上述结果表明，雄性会根据自身属性选择适配的交配策略。尽管不同策略下雄性获得的繁殖成功率相近，这提示这些替代性策略或可使每只雄性的父权收益均达到最大化。虽然父权收益的近因机制可能受雄性或雌性单方调控，但本研究证实，雄性性表型的诸多相互关联的组分，会影响其决策规则的演化，从而加深了我们对性选择背景下交配策略如何演化的理解。