Earl Alexis D, Carter Gerald G, Berlinger Arden G, Korir Elkana, Shah Shailee S, Watetu Wilson N, Rubenstein Dustin R
Department of Ecology, Evolution, and Environmental Biology, Columbia University, New York, NY, USA.
Mpala Research Centre, Nanyuki, Kenya.
Nature. 2025 May 7. doi: 10.1038/s41586-025-08958-4.
Identifying the mechanisms that underlie cooperation is fundamental to biology. The most complex form of cooperation in vertebrates occurs in cooperative breeders, in which helpers forego reproduction and assist in raising the young of others, typically relatives. Not all cooperative societies, however, are kin-based-nearly half of all avian and mammalian cooperative breeders form mixed-kin societies, much like those of humans. Kin selection in mixed-kin societies occurs when individuals gain indirect fitness from the preferential helping of relatives, but helpers also frequently assist non-kin, highlighting a potential role for direct fitness in stabilizing cooperative societies. Here, using a 20-year study of superb starlings (Lamprotornis superbus), we examined how direct and indirect fitness jointly influence helping behaviour. Although we detected kin-biased helping (demonstrating kin selection), non-kin helping was common despite opportunities to aid kin. Unexpectedly, specific pairs maintained long-term reciprocal helping relationships by swapping social roles across their lifetimes-a subtle pattern of reciprocity requiring decades of observation to detect. Given the frequency of non-kin helping and the occurrence of reciprocal helping among both kin and non-kin, helping behaviour in superb starlings seems to be greatly influenced by direct fitness. However, the relative importance of direct and indirect fitness varied with helpers' sex and dispersal history. By uncovering a cryptic yet crucial role of long-term reciprocal helping, we suggest that reciprocity may be an underappreciated mechanism promoting the stability of cooperatively breeding societies.
识别合作背后的机制是生物学的基础。脊椎动物中最复杂的合作形式出现在合作繁殖者中，其中帮手放弃繁殖并协助抚养其他个体的幼崽，通常是亲属的幼崽。然而，并非所有合作群体都是基于亲属关系的——几乎一半的鸟类和哺乳动物合作繁殖者形成了混合亲属群体，与人类的群体非常相似。在混合亲属群体中，当个体通过优先帮助亲属获得间接适应性时，亲属选择就会发生，但帮手也经常帮助非亲属，这凸显了直接适应性在稳定合作群体中的潜在作用。在这里，通过对华丽椋鸟（Lamprotornis superbus）进行的一项为期20年的研究，我们研究了直接适应性和间接适应性如何共同影响帮助行为。尽管我们检测到了亲属偏向的帮助行为（证明了亲属选择），但尽管有机会帮助亲属，非亲属帮助行为仍然很常见。出乎意料的是，特定的配对通过在其一生中交换社会角色维持了长期的互惠帮助关系——这是一种微妙的互惠模式，需要数十年的观察才能发现。鉴于非亲属帮助行为的频率以及亲属和非亲属之间都存在互惠帮助行为，华丽椋鸟的帮助行为似乎受到直接适应性的极大影响。然而，直接适应性和间接适应性的相对重要性因帮手的性别和扩散历史而异。通过揭示长期互惠帮助的一个隐秘但至关重要的作用，我们认为互惠可能是一种未得到充分重视的促进合作繁殖群体稳定性的机制。
