Data from: Spatial and temporal escape from fungal parasitism in natural communities of anciently asexual bdelloid rotifers

Sexual reproduction is costly, but it is nearly ubiquitous among plants and animals, whereas obligately asexual taxa are rare and almost always short-lived. The Red Queen hypothesis proposes that sex overcomes its costs by enabling organisms to keep pace with coevolving parasites and pathogens. If so, the few cases of stable long-term asexuality ought to be found in groups whose coevolutionary interactions with parasites are unusually weak. In theory, antagonistic coevolution will be attenuated if hosts disperse among patches within a metapopulation separately from parasites and more rapidly. We examined whether these conditions are met in natural communities of bdelloid rotifers, one of the longest-lived asexual lineages. At any life stage, these microscopic invertebrates can tolerate the complete desiccation of their ephemeral freshwater habitats, surviving as dormant propagules that are readily carried by the wind. In our field experiments, desiccation and wind transport enabled bdelloids to disperse independently of multiple fungal parasites, in both time and space. Surveys of bdelloid communities in unmanipulated moss patches confirmed that fungal parasitism was negatively correlated with extended drought and increasing height (exposure to wind). Bdelloid ecology therefore matches a key condition of models in which asexuals persist through spatio-temporal decoupling from coevolving enemies.

有性生殖虽需付出高昂演化成本，但在动植物类群中几乎普遍存在；而专性无性类群则极为罕见，且几乎均为短命类群。红皇后假说（Red Queen hypothesis）提出，有性生殖可通过帮助生物跟上协同演化的寄生虫与病原体的演化节奏，从而抵消其自身的成本。若该假说成立，则稳定持久的无性生殖案例，理应出现在那些与寄生虫的协同演化互动异常微弱的类群中。理论上，若宿主在集合种群（metapopulation）的各斑块间的扩散过程独立于寄生虫，且扩散速度快于寄生虫，则拮抗协同演化会被弱化。我们以蛭形轮虫（bdelloid rotifers）——已知存续时间最久的无性演化支系之一——的自然群落为研究对象，检验这些条件是否得以满足。这类微型无脊椎动物在其生命周期的任一阶段，均可耐受其短暂淡水生境的完全干燥，以休眠繁殖体的形式存活，并可通过风力轻松扩散。在我们的野外实验中，干燥作用与风力输运使得蛭形轮虫能够在时间与空间维度上，独立于多种真菌寄生虫完成扩散。对未受人为干预的苔藓斑块中的蛭形轮虫群落的调查显示，真菌寄生率与持续干旱时长呈负相关，同时也随斑块高度（即暴露于风力的程度）增加而降低。因此，蛭形轮虫的生态特征恰好契合了无性类群通过与协同演化天敌在时空维度上解耦，从而得以存续的模型关键条件。