Data from: Neutral processes forming large clones during colonization of new areas

In species reproducing both sexually and asexually clones are often more common in recently established populations. Earlier studies have suggested that this pattern arises due to natural selection favouring generally or locally successful genotypes in new environments. Alternatively, as we show here, this pattern may result from neutral processes during species’ range expansions. We model a dioecious species expanding into a new area in which all individuals are capable of both sexual and asexual reproduction, and all individuals have equal survival rates and dispersal distances. Even under conditions that favour sexual recruitment in the long run, colonisation starts with an asexual wave. After colonisation is completed, a sexual wave erodes clonal dominance. If individuals reproduce more than one season, and with only local dispersal, a few large clones typically dominate for thousands of reproductive seasons. Adding occasional long-distance dispersal, more dominant clones emerge, but they persist for a shorter period of time. The general mechanism involved is simple: edge effects at the expansion front favour asexual (uniparental) recruitment where potential mates are rare. Specifically, our model shows that neutral processes (with respect to genotype fitness) during the population expansion, such as random dispersal and demographic stochasticity, produce genotype patterns that differ from the patterns arising in a selection model. The comparison with empirical data from a postglacially established seaweed species (Fucus radicans) shows that in this case a neutral mechanism is strongly supported.在兼具有性与无性繁殖的物种中，克隆群体在新近建立的种群中往往更为常见。此前的研究认为，该现象源于自然选择对新环境中全局适配或本地适配的基因型的青睐。而本研究表明，该现象也可能源于物种分布区扩张过程中的中性演化过程。本研究构建了一个雌雄异株（dioecious）物种的扩张模型：该物种所有个体均可进行有性与无性繁殖，且所有个体的存活率与扩散距离均一致。即便长期来看环境更有利于有性繁殖定植，种群定植仍以无性繁殖波的形式启动。定植完成后，有性繁殖波会逐渐削弱克隆的优势地位。若个体可进行多季繁殖且仅存在本地扩散，则少数大型克隆通常可占据优势达数千个繁殖季。若引入偶发的长距离扩散，则会出现更多优势克隆，但它们的优势持续时间会更短。其核心机制十分简单：扩张前沿的边缘效应会在潜在交配对象稀缺的环境下，更有利于无性（单亲）繁殖的定植。具体而言，本模型表明，种群扩张过程中与基因型适合度无关的中性过程（如随机扩散与人口统计学随机性）所产生的基因型分布模式，与选择模型下的分布模式存在显著差异。通过与冰期后定植的海藻物种囊岩藻（Fucus radicans）的实测数据对比，本研究发现该案例中的分布模式可由中性机制得到有力支持。