Shah Shailee S, Rubenstein Dustin R
Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, New York, USA.
Center for Integrative Animal Behavior, Columbia University, New York, New York, USA.
J Anim Ecol. 2025 Mar;94(3):356-367. doi: 10.1111/1365-2656.14162. Epub 2024 Aug 5.
Many cooperatively breeding species live in groups with complex structure-large group sizes, low and variable kin structure, and multiple breeding pairs. Since these mixed-kin groups typically form because of immigration of unrelated individuals of both sexes in addition to limited offspring dispersal, differences in patterns of dispersal can generate variation in group structure, even within the same species or population. Here, we examine how environmentally mediated dispersal patterns influence variation in group structure in the plural breeding superb starling (Lamprotornis superbus), an avian cooperative breeder that inhabits a spatiotemporally variable savanna environment and forms mixed-kin groups with variable group sizes and more than one breeding pair per group. Using 4068 genome-wide polymorphic loci and fine-scale, remotely sensed ecological data from 22 groups sampled across a nearly 200 km environmental gradient in central Kenya, we find evidence of not only frequent and long-distance dispersal in both sexes (low isolation-by-distance and weak genetic structure), but also directional dispersal from small groups in lower quality habitat with low normalised difference vegetation index (NDVI) to large groups in higher quality habitat with high NDVI. Additionally, we find stronger genetic structure among groups in lower quality habitat, and higher genetic diversity and lower relatedness of groups in higher quality habitat. Previous work using long-term data from groups in the same population has shown that groups with lower relatedness are larger and have more breeding pairs. Long-distance, directional dispersal to maximise individual fitness can thus lead to smaller and simpler kin-based social groups in lower quality habitat, but larger and more complex mixed-kin groups in higher quality habitat. Such intraspecific, within-population variation in group structure, including variation in kin structure of social groups, could have profound implications for the relative importance of the evolutionary mechanisms (i.e. direct vs. indirect fitness benefits) underlying the formation of cooperative societies.
许多合作繁殖的物种生活在结构复杂的群体中——群体规模大、亲缘结构低且多变，还有多对繁殖个体。由于这些混合亲缘群体的形成通常是因为除了有限的后代扩散外，两性无关个体的迁入，扩散模式的差异会导致群体结构的变化，即使在同一物种或种群内也是如此。在这里，我们研究环境介导的扩散模式如何影响多配偶繁殖的超级椋鸟（Lamprotornis superbus）群体结构的变化，超级椋鸟是一种合作繁殖的鸟类，栖息在时空多变的稀树草原环境中，形成了群体规模可变且每组有多对繁殖个体的混合亲缘群体。利用4068个全基因组多态性位点以及来自肯尼亚中部近200公里环境梯度上采样的22个群体的精细尺度遥感生态数据，我们发现不仅两性都有频繁且远距离的扩散（距离隔离低且遗传结构弱），而且存在从归一化植被指数（NDVI）低的低质量栖息地的小群体向NDVI高的高质量栖息地的大群体的定向扩散。此外，我们发现在低质量栖息地的群体间遗传结构更强，而在高质量栖息地的群体遗传多样性更高且亲缘关系更低。之前对同一种群中各群体的长期数据研究表明，亲缘关系较低的群体更大且繁殖对更多。因此，为了使个体适应性最大化的长距离定向扩散会导致低质量栖息地中基于亲缘关系的社会群体更小、更简单，但在高质量栖息地中会形成更大、更复杂的混合亲缘群体。这种群体结构的种内、种群内变异，包括社会群体亲缘结构的变异，可能对合作社会形成背后的进化机制（即直接与间接适应性益处）的相对重要性产生深远影响。
