Data from: Delayed dispersal and prolonged brood care in a family-living beetle

Delayed juvenile dispersal is an important prerequisite for the evolution of family-based social systems, such as cooperative breeding and eusociality. In general, young adults forego dispersal if there are substantial benefits to remaining in the natal nest and/or the likelihood of dispersing and breeding successfully is low. We investigate some general factors thought to drive delayed juvenile dispersal in the horned passalus beetle, a family-living beetle in which young adults remain with their families in their natal nest for several months before dispersing. Fine scale population genetic structure indicated high gene flow between nest sites, suggesting that constraints on mobility are unlikely to explain philopatry. Young adults do not breed in their natal log and likely disperse before reaching breeding age, suggesting that they do not gain direct reproductive benefits from delayed dispersal. We also examined several ways in which parents might incentivize delayed dispersal by providing prolonged care to adult offspring. Although adult beetles inhibit fungal growth in the colony by manipulating both the nest-site and deceased conspecifics, this is unlikely to be a major explanation for family living since both parents and adult offspring seem capable of controlling fungal growth. Adult offspring that stayed with their family groups also neither gained more mass nor experienced faster exoskeleton development than those experimentally removed from their families. The results of these experiments suggest that our current understanding of the factors underlying prolonged family living may be insufficient to explain delayed dispersal in at least some taxa, particularly insects.

延迟幼体扩散（delayed juvenile dispersal）是合作繁殖（cooperative breeding）、真社会性（eusociality）等基于家庭的社会系统演化的重要前提。一般而言，若留在出生巢（natal nest）中可获得显著收益，或扩散并成功繁殖的概率较低时，年轻成虫会放弃扩散。本研究针对角磨蜣甲虫（horned passalus beetle）探究了驱动其延迟幼体扩散的若干通用影响因素；该类营家庭生活的甲虫中，年轻成虫会在扩散前与家族一同留在出生巢中长达数月之久。精细尺度的种群遗传结构分析结果显示，不同巢位间存在较高的基因流，这表明活动能力限制不太可能解释其恋巢性（philopatry）。年轻成虫并不会在其出生的朽木巢中繁殖，且大概率会在达到繁殖年龄前完成扩散，这表明它们无法从延迟扩散中获得直接的繁殖收益。本研究同时探究了亲本可通过对成年后代提供长期抚育，从而激励延迟扩散的若干潜在路径。尽管成年甲虫可通过调控巢位环境与处理死亡同种个体（conspecifics），来抑制种群内的真菌生长，但这不太可能成为解释其家庭群居的主要原因——因为亲本与成年后代似乎均具备控制真菌生长的能力。与家族群体一同停留的成年后代，其体重增长速率与外骨骼（exoskeleton）发育速度，均未显著高于实验中被移出家族的成年后代。上述实验结果表明，我们目前对长期家庭群居背后影响因素的认知，或许不足以解释至少部分类群的延迟扩散现象，尤其是昆虫类群。