Abstract

Family living is a stepping stone to higher-order social structures including cooperatively breeding groups, but understanding why offspring remain with parents by delaying dispersal remains a challenge. One rarely studied aspect of family living is communal huddle roosting, where individuals group together overnight for thermoregulatory and/or anti-predator benefits. Here, we use a PIT-tag detection system to investigate the potential for direct and indirect nepotism in roosting huddles of cooperatively breeding chestnut-crowned babblers (Pomatostomus ruficeps) living in extended families with female immigrants. This species habitually roosts communally in single-chambered domed nests; an average of 8.5 (± 4.4 SD) individuals taking ~6 min to enter roost nests roosted together in this study. We found that the order in which individuals settled in the roost was negatively associated with their exit order, and those settling late were more likely to be detected at the nest entrance during the night, suggesting that settlement order influences individual roosting positions. Juveniles entered the roost in mid-rank positions, and their entries were associated with increased activity levels of carers, suggesting direct nepotistic assistance. In addition, immigrant females more often settled in the roosts later than others, suggesting indirect nepotism through exclusion of immigrants from more central roosting positions. This exclusion was not obviously confounded by age or sex. As those settling later are expected to experience reduced thermoregulatory benefits and increased predation risk, our results suggest that direct and indirect nepotistic benefits during communal roosting might offer part of the explanation for family living through delayed dispersal in this species.

Significance statement

Nepotism—preferential treatment towards kin or against non-kin—may lead to individuals benefiting from staying in their natal group rather than dispersing, and so increasing the propensity for family living and the subsequent evolution of cooperative breeding. One possible route through which delayed dispersers might gain nepotistic benefits is in communal roosting huddles, as individuals roosting more centrally are likely to receive greater thermoregulatory and/or predator avoidance benefits. To our knowledge, studies have yet to discover an advantage of natal individuals beyond care received as young during communal roosting. We show that immigrant females settle in the communal roosts later than nutritionally independent natal females and may occupy peripheral positions in roosts of the cooperatively breeding chestnut-crowned babbler (Pomatostomus ruficeps) using a remote PIT-tag system. This apparent immigrant disadvantage might be significant in promoting delayed dispersal.

中文翻译：

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共同栖息地显示了由板栗加冠ba皮匠直接和间接裙带关系所预测的动态

摘要

家庭生活是包括合作育种小组在内的更高级别社会结构的垫脚石，但是要了解为什么后代通过延迟分散而留在父母身边仍然是一个挑战。家庭生活中很少有人研究的方面是杂乱无章的栖身之所，在这里，人们聚在一起过夜以获得体温调节和/或抗捕食者的好处。在这里，我们使用PIT标签检测系统调查合作繁殖栗子冠ba皮鱼（Pomatostomus ruficeps）栖居时的直接和间接裙带关系）与女性移民居住在大家庭中。该物种习惯性地栖息在单室圆顶巢中。在这项研究中，平均8.5（±4.4 SD）个人需要约6分钟才能进入栖息的巢穴。我们发现，个体在栖息地定居的顺序与他们的出境顺序呈负相关，而较晚安顿的人更有可能在夜间在鸟巢入口处被发现，这表明沉降顺序会影响个体的栖息位置。幼体进入中间位置的栖息地，它们的进入与护理人员活动水平的提高有关，表明直接的裙带关系援助。此外，移民女性比其他人更常在栖息地定居，建议通过将移民排除在更中央的居住位置而间接地裙带关系。这种排除显然不受年龄或性别的困扰。由于后来定居的人们预计将减少体温调节效益，并增加捕食风险，因此我们的研究结果表明，在公共栖息地期间直接和间接的裙带关系可能通过延迟在该物种中传播而为家庭生活提供了部分解释。

重要性声明

裙带关系（对亲属或非亲属的优惠待遇）可能导致个人受益于其出生群体而不是分散，从而增加了家庭生活的倾向以及随后合作育种的发展。延迟分散器可能获得裙带关系收益的一种可能途径是在公共栖息地挤成一团，因为在中心地处栖息的人可能会获得更大的温度调节和/或避免捕食者的好处。据我们所知，研究还没有发现出生期间个体在公共栖息地期间获得照顾之外的优势。我们显示，移民女性比有营养独立的成年女性晚于公共栖息地定居，并且可能在合作繁殖栗子冠cr皮鱼的栖息地中占据外围位置（使用远程PIT标签系统的Pomatostomus ruficeps）。这种明显的移民不利条件可能对促进延迟的散布很重要。