Abstract Neighbour-stranger discrimination is widespread in territorial animals, and depending on the relative threat posed by neighbours and strangers, residents commonly exhibit either the “dear enemy phenomenon” or the “nasty neighbour effect”. Different members of the same group may represent different threat levels, and the response of residents can be modified depending on, e.g. the sex and dominance status of the intruder. Neighbour-stranger discrimination is primarily investigated in neighbours with shared borders, and whether residents recognize their more distant neighbours remains unexplored. Here, using experimental scent marks, we investigated whether Eurasian beavers ( Castor fiber ) discriminate between distant neighbours (i.e. two territories away) and strangers (i.e. further away than the known dispersal distance). We tested the hypotheses that Eurasian beavers can discriminate between distant neighbours and strangers and that social status (i.e. sub-dominant or dominant) and sex of the intruder affect the responses of resident beavers. We predicted that resident beavers show the “dear enemy phenomenon” in response towards dominant distant neighbours due to their territory ownership and the “nasty neighbour effect” in response towards sub-dominants due to their likelihood to disperse. Sex of residents and social status of intruders were important in explaining territorial responses, with males exhibiting stronger responses to sub-dominant distant neighbours, especially males, than sub-dominant strangers. No such discrimination was found by females or between dominant distant neighbours and strangers. We suggest that the “nasty neighbour” response by male resident beavers towards sub-dominant distant neighbours relates to the relative threat levels due to repeated intrusions during dispersal attempts. Significance statement Territorial animals discriminate between neighbours and strangers to allocate aggressive behaviour to conspecific intruders. This neighbour-stranger discrimination has primarily been investigated between adjacent neighbours, but extraterritorial movements of residents into distant territories occur. Whether residents can discriminate between distant neighbours and strangers has only been studied in skylarks ( Alauda arvensis ), based on acoustic communication. Yet, it is unknown whether distant neighbours are perceived as neighbours or strangers based on olfactory recognition. Here we investigated whether Eurasian beavers ( C. fiber ) can discriminate between distant neighbours (i.e. two territories away) and strangers, based on olfactory scent samples including information on social status (i.e. dominant or sub-dominant) and sex of the intruder. Our results show that male residents showed a “nasty neighbour” response towards sub-dominant distant neighbours. These findings highlight the sensitivity of territorial mammals to the familiarity and social status of intruders.

中文翻译：

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远方的邻居：朋友还是敌人？欧亚海狸对模拟入侵者表现出依赖环境的反应

摘要 邻里歧视在领地动物中普遍存在，根据邻居和陌生人构成的相对威胁，居民通常表现出“亲爱的敌人现象”或“讨厌的邻居效应”。同一组的不同成员可能代表不同的威胁级别，并且可以根据例如入侵者的性别和支配地位来修改居民的反应。邻居-陌生人歧视主要在有共同边界的邻居中进行调查，居民是否认识他们更远的邻居仍有待探索。在这里，我们使用实验性气味标记研究欧亚海狸（蓖麻纤维）是否区分远方（即两个领土之外）和陌生人（即比已知的分散距离更远）。我们测试了欧亚海狸可以区分远方邻居和陌生人以及入侵者的社会地位（即次优势或优势）和性别影响常驻海狸反应的假设。我们预测，常驻海狸由于其领土所有权而表现出对占主导地位的远方邻居的“亲爱的敌人现象”和对次优势的“讨厌的邻居效应”，因为他们可能会分散。居民的性别和入侵者的社会地位对于解释领土反应很重要，男性对次主导的远方邻居，尤其是男性，比次主导的陌生人表现出更强的反应。女性或占主导地位的远方邻居和陌生人之间没有发现这种歧视。我们认为，雄性居民海狸对次优势远邻的“讨厌的邻居”反应与由于分散尝试期间反复入侵而导致的相对威胁水平有关。意义声明 领地动物区分邻居和陌生人，将攻击行为分配给同种入侵者。这种邻居-陌生人歧视主要是在相邻邻居之间进行调查，但居民向遥远领土的域外迁移时有发生。居民是否可以区分远方的邻居和陌生人，仅在云雀 (Alauda arvensis) 中进行了研究，基于声学通信。然而，基于嗅觉识别，远方的邻居是否被认为是邻居或陌生人是未知的。在这里，我们调查了欧亚海狸 (C. fiber) 是否可以根据嗅觉样本区分远方的邻居（即两个领土之外）和陌生人，包括社会地位（即优势或次优势）和入侵者性别的信息。我们的结果表明，男性居民对次要的远方邻居表现出“讨厌的邻居”的反应。这些发现强调了领地哺乳动物对入侵者的熟悉程度和社会地位的敏感性。