Rafajlović M, Kleinhans D, Gulliksson C, Fries J, Johansson D, Ardehed A, Sundqvist L, Pereyra R T, Mehlig B, Jonsson P R, Johannesson K
Department of Physics, University of Gothenburg, Gothenburg, Sweden.
The Linnaeus Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.
J Evol Biol. 2017 Aug;30(8):1544-1560. doi: 10.1111/jeb.13124. Epub 2017 Jun 25.
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, colonization starts with an asexual wave. After colonization 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 post-glacially established seaweed species (Fucus radicans) shows that in this case, a neutral mechanism is strongly supported.
在既能进行有性繁殖又能进行无性繁殖的物种中，克隆体在新建立的种群中往往更为常见。早期研究表明，这种模式的出现是由于自然选择有利于新环境中普遍或局部成功的基因型。或者，正如我们在此所展示的，这种模式可能源于物种范围扩张过程中的中性过程。我们构建了一个雌雄异株的物种扩展到一个新区域的模型，在这个区域中所有个体都能进行有性和无性繁殖，并且所有个体具有相等的存活率和扩散距离。即使从长远来看有利于有性繁殖的条件下，定殖也是以无性繁殖浪潮开始的。定殖完成后，有性繁殖浪潮会削弱克隆优势。如果个体繁殖超过一个季节，并且仅进行局部扩散，一些大型克隆体通常会在数千个繁殖季节中占据主导地位。偶尔增加长距离扩散，会出现更多占主导地位的克隆体，但它们持续的时间较短。所涉及的一般机制很简单：扩张前沿的边缘效应有利于在潜在配偶稀少的地方进行无性（单亲）繁殖。具体而言，我们的模型表明，种群扩张过程中的中性过程（相对于基因型适应性），如随机扩散和人口统计学随机性，产生的基因型模式与选择模型中产生的模式不同。与一种后冰川期建立的海藻物种（鹿角菜）的实证数据比较表明，在这种情况下，强烈支持中性机制。
