Abstract

Territorial animals often respond less aggressively to neighbours than strangers. This ‘dear enemy’ effect is hypothesized to be adaptive by reducing unnecessary aggressive interactions with non-threatening individuals. A key prediction of this hypothesis, that individual fitness will be affected by variation in the speed and the extent to which individuals reduce their aggression towards neighbours relative to strangers, has never been tested. We used a series of song playbacks to measure the change in response of male great tits to a simulated establishment of a neighbour on an adjacent territory during early stages of breeding, as an assay of individuals’ tendencies to form dear enemy relationships. Males reduced their approach to the speaker and sang fewer songs on later playback repetitions. However, only some males exhibited dear enemy behaviour by responding more strongly to a subsequent stranger playback, and when the playback procedure was repeated on a subset of males, there was some indication for consistent differences among individuals in the expression of dear enemy behaviour. We monitored nests and analysed offspring paternity to determine male reproductive success. Individuals that exhibited dear enemy behaviour towards the simulated neighbour did not suffer any costs associated with loss of paternity, but there was also no evidence of reproductive benefits, and no net effect on reproductive fitness. The general ability to discriminate between neighbours and strangers is likely adaptive, but benefits are probably difficult to detect because of the indirect link between individual variation in dear enemy behaviour and reproductive fitness and because of the complex range of mechanisms affecting relations with territorial neighbours.

Significance statement

The dear enemy effect, in which animals respond less aggressively to familiar neighbours compared to strangers, is probably beneficial because it reduces aggressive interactions with non-threatening individuals. However, no study has ever tested whether there actually are fitness benefits for individuals with a greater tendency to form dear enemy relationships. Our study used experimental playbacks to simulate neighbours and strangers, and we found no relationship between dear enemy behaviour and reproductive success in a songbird. However, our approach to test adaptive hypotheses of this widespread territorial behaviour and our longitudinal playback design to examine the development of familiarity towards a neighbour and discrimination of neighbours and strangers are likely to be important tools to advance our understanding of territorial behaviour and individual recognition.

中文翻译：

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领土鸣禽的敌对行为没有生殖健康益处

摘要

领地动物对邻居的反应通常不如陌生人那么激进。这种“亲爱的敌人”效应被假设为通过减少与非威胁个体的不必要的攻击性互动而具有适应性。这一假设的一个关键预测，即个体适应度将受到速度变化的影响，以及个体相对于陌生人减少对邻居的攻击性的程度，从未被测试过。我们使用一系列歌曲回放来测量雄性大山雀在繁殖的早期阶段对邻近领土上模拟建立邻居的反应变化，作为个体形成亲密敌人关系的倾向的分析。男性减少了他们对演讲者的接近，并且在以后的重复播放中唱的歌曲更少。然而，只有一些雄性通过对随后的陌生人回放做出更强烈的反应而表现出亲密的敌人行为，并且当回放过程在一部分雄性身上重复时，有迹象表明个体之间在亲密敌人行为的表达上存在一致的差异。我们监测巢穴并分析后代亲子关系以确定雄性繁殖成功率。对模拟邻居表现出敌对行为的个体没有遭受与失去亲子关系相关的任何成本，但也没有证据表明生殖益处，也没有对生殖健康的净影响。区分邻居和陌生人的一般能力可能是适应性的，

意义陈述

亲爱的敌人效应，动物对熟悉的邻居的反应比陌生人的攻击性低，这可能是有益的，因为它减少了与非威胁个体的攻击性互动。然而，没有研究测试过对于更倾向于形成敌对关系的个人是否真的有健身益处。我们的研究使用实验回放来模拟邻居和陌生人，我们发现在鸣禽的亲敌行为和繁殖成功之间没有关系。然而，