Data from: Threat sensitive adjustment of aggression by males and females in a biparental cichlid

Defending offspring provides fitness benefits to parents, but is costly. To moderate costs, parents should adjust aggressive responses to the threat posed by different species entering their territory. However, few studies have experimentally tested behavioral adjustments in response to the threat posed by different types of intruders, particularly in the field, and in environments with an array of heterospecific intruders. Here, using a biparental cichlid, the poor man’s tropheus (Hypsophrys nematopus), we investigated whether males and females in the wild invest equally into offspring defense and what impact the absence of a partner might have on the quality of offspring defense provided by a solitary parent. In a separate experiment, we assessed responses of breeding pairs to three common heterospecific intruders that pose different levels of threat to the breeding pair and their brood. We found that both paired and unpaired females invested significantly more into territorial aggression than males. However, unpaired females were unable to fully compensate for the absence of their partner, with intruders left to venture closer to their offspring. Furthermore, we show that breeding pairs can readily discriminate between heterospecific intruders, with pairs responding quicker and more aggressively towards species that posed a greater potential threat. Our results demonstrate that biparental species can have extensive behavioral flexibility in their aggressive responses towards intruders, even in environments with a high frequency of territory incursion. The quality of territorial defense can nevertheless be compromised if one parent is left to defend the brood alone.

保卫子代可为亲代带来进化适合度（fitness）收益，但同时需付出相应代价。为缓解此类防御成本，亲代应针对进入其领地的不同物种所构成的威胁，灵活调整自身的攻击响应策略。然而，目前鲜有研究通过实验探究亲代针对不同类型入侵者威胁的行为调节机制，尤其是在野外环境以及存在多种异种入侵者（heterospecific intruders）的自然场景中。本研究以双亲抚育（biparental）的慈鲷物种贫民慈鲷（Hypsophrys nematopus，俗称the poor man’s tropheus）为研究对象，探究了野外种群中雌雄个体是否会对等投入子代保卫行为，以及配偶缺失会对单亲抚育子代的防御行为质量产生何种影响。在另一项独立实验中，我们评估了繁殖配对对三种常见异种入侵者的响应——这三类入侵者对繁殖配对及其幼巢（brood）构成不同程度的威胁。研究结果显示，无论是否有配偶陪伴，雌性个体的领地攻击（territorial aggression）投入均显著高于雄性。但单亲雌性无法完全弥补配偶缺失带来的防御缺口，入侵者得以更接近其幼代。此外，本研究证实繁殖配对可快速区分不同异种入侵者，对潜在威胁更高的物种会做出更快、更激烈的攻击响应。本研究结果表明，双亲抚育物种在针对入侵者的攻击行为中具备极强的行为灵活性，即便在领地入侵频发的环境中亦是如此。但若仅剩单亲负责抚育防御，领地保卫的质量仍会受到损害。