Avian promiscuity in the last European primeval forest

Primeval forests provide a reference point to understand the origins and evolution of mating systems because they offer a unique, undisturbed environment where natural selection and ecological interactions play out in their original context. We established rates of extra-pair paternity (EPP) for two bird species referential to evolutionary ecology: blue tit and great tit, breeding in natural cavities of the sole remnant of European lowland primeval forests preserved in Białowieża National Park. Genotype-by-sequencing of 889 blue tits and 1,256 great tits revealed that 48% of blue tit broods and 39% great tit broods were of mixed paternity, with 15% blue tit and 14% great tit nestlings not sired by their social father. These referential levels align with median values of EPP reported in nestbox studies in secondary and managed forests, suggesting that certain reproductive strategies are advantageous across diverse environments. Observed promiscuity levels did not affect reproductive success or parental investment, indicating no or limited adaptive value for promiscuity in the context of a primeval forest ecosystem. Our study underscores how primeval habitats provide unparalleled insights into natural selection and mating strategies in wild populations, highlighting the stability and resilience of these strategies across different environmental contexts.原始森林为理解婚配系统的起源与演化提供了核心参照基准，因其拥有独特且未受人为干扰的环境，能让自然选择与生态相互作用在原生背景下完整呈现。我们针对进化生态学研究中的两种标志性鸟类——蓝山雀（blue tit）与大山雀（great tit），测定了其婚外父权（extra-pair paternity, EPP）的发生率。这两种鸟类在波兰比亚沃维耶扎国家公园内仅存的欧洲低地原始森林遗迹的天然树洞中筑巢繁殖。本研究对889只蓝山雀与1256只大山雀开展基因型测序（Genotype-by-sequencing）分析，结果显示：48%的蓝山雀巢窝与39%的大山雀巢窝存在混合父权现象，其中15%的蓝山雀雏鸟与14%的大山雀雏鸟并非由其社会父亲所抚育。上述参照性的父权发生率数据，与次生林及人工经营林中巢箱研究报道的婚外父权发生率中位数相符，表明部分繁殖策略在多样环境中均具备适应性优势。观测到的滥交水平并未对繁殖成功率或亲本投入产生影响，这说明在原始森林生态系统的背景下，滥交行为几乎不具备或仅具备有限的适应性价值。本研究凸显了原始生境如何为野生种群的自然选择与婚配策略研究提供无可比拟的研究视角，同时证实了这些策略在不同环境背景下的稳定性与韧性。