Data from: Dispersal and establishment traits provide a colonization advantage for a polyploid apomictic plant

AbstractPremise: Apomictic plants (reproducing asexually through seed) often have larger ranges and occur at higher latitudes than closely related sexuals, a pattern known as geographical parthenogenesis (GP). Explanations for GP include differences in colonizing ability due to reproductive assurance and direct/indirect effects of polyploidy (most apomicts are polyploid) on ecological tolerances. While life history traits associated with dispersal and establishment also contribute to the potential for range expansion, few studies compare these traits in related apomicts and sexuals.  Methods: We investigated differences in early life history traits between diploid-sexual and polyploid-apomictic Townsendia hookeri (Asteraceae), which displays a classic pattern of GP. Using lab and greenhouse experiments, we measured seed dispersal traits, germination success, and seedling size and survival in sexual and apomictic populations from across the range.  Key Results: While theory predicts that trade-offs between dispersal and establishment traits should be common, this was largely not the case in T. hookeri. Apomictic seeds had both lower terminal velocity (staying aloft longer when dropped) and higher germination success than sexual seeds. While there were no differences in seedling size between reproductive types, apomicts did, however, have slightly lower seedling survival than sexuals.  Conclusions: These differences in early life history traits, combined with reproductive assurance conferred by apomixis, suggest that apomicts achieve a greater range through advantages in their ability to both spread and establish. 
MethodsStudy system Townsendia hookeri is a diminutive perennial member of the sunflower family (Asteraceae) with two forms: diploids that reproduce sexually and autopolyploids (mainly triploids) that reproduce via gametophytic apomixis (Beaman1957; Thompson and Whitton 2006). Sexual individuals are self-incompatible, while apomicts set seed autonomously, without the need for pollen to fertilize the endosperm. Townsendia hookeri produces single-seeded diaspores with persistent feathery pappus bristles (Strother 1993) usually associated with wind dispersal (Andersen 1992). Despite differing in ploidy and reproductive mode, the two forms are macro-morphologically indistinguishable in the field but can be distinguished by pollen traits. Polyploids produce larger viable pollen grains than diploids and have much lower pollen viability. To date, our lab group has characterized more than 90 populations throughout the species’ range and found a tight association between low pollen viability and larger genome size (Thompson & Whitton 2006; Garani 2014; Lee 2015), supporting Beaman’s (1957) contention that diploids are sexual and polyploids are apomictic (Thompson & Whitton 2006; Thompson et al. 2008). Sexual populations have a much smaller range than the apomicts and primarily occur between Boulder, CO and Laramie, WY (Lee 2015). Apomictic populations extend from southern WY along the eastern side of the Rocky Mountains as far north as BC, Canada. In addition, a small number of diploid-sexual and polyploid-apomict populations occurs in a disjunct distribution in the Yukon territory (Thompson & Whitton 2006; Garani 2014). Seed dispersal traits and terminal velocity measurements and analysis We compared diaspore traits of apomicts and sexuals using field-collected diaspores (technically cypselae, but from now on referred to as “seeds”) obtained between 2008 and 2013 from five diploid sexual and seven polyploidapomictic populations from across T. hookeri’s range, including northern populations in British Columbia and the Yukon territory (Appendix S1, Table S1; see the Supplementary Data with this article).  We selected two seeds from each of up to ten maternal plants per population, using only filled and darkly coloured seeds (traits that indicate viability; Garani 2014) with an intact pappus. In order to restore the pappus to a comparably open state (relative to the somewhat flattened state that resulted from storage in the collection envelopes), we placed seeds on wet filter paper in a sealed petri dish for ∼24 hours, then removed them and allowed them to air-dry for another 24 hours. At this point, the pappus had achieved a more regular form consistent with what is seen at the time of field collection. For each seed, we estimated the mass using an analytical balance, recorded the number of pappus bristles, and measured the length of two bristles from the center-apex using an ocular micrometer. We measured the angle of attack, the maximum angle across the open pappus bristles centered on their point of attachment to the seed proper, using a protractor (see Figure 2 in O’Connell and Eckert (2001) for a diagram depicting diaspore traits). We estimated terminal velocity by dropping individual seeds down a clear 120 cm long acrylic glass tube. Seeds were dropped by holding the pappus with tweezers and...

无融合生殖植物（apomictic plants，通过种子进行无性繁殖的物种）通常比其近缘有性类群拥有更广的分布范围，且分布纬度更高，这一现象被称为地理孤雌生殖（geographical parthenogenesis，GP）。针对地理孤雌生殖的解释包括：由生殖保障带来的定植能力差异，以及多倍体（polyploidy，多数无融合生殖类群均为多倍体）对生态耐受度的直接/间接影响。尽管与扩散和定植相关的生活史性状同样会影响物种的分布扩张潜力，但目前鲜有研究在近缘的无融合生殖类群与有性类群间对这些性状进行比较。

【研究方法】本研究以呈现典型地理孤雌生殖模式的哈氏 Townsendia（Townsendia hookeri，菊科Asteraceae）为研究对象，探究其二倍体有性生殖种群与多倍体无融合生殖种群间的早期生活史性状差异。研究通过室内实验与温室栽培，对该物种全分布范围内的有性与无融合生殖种群的种子扩散性状、萌发成功率，以及幼苗大小与存活率进行了测定。

【核心结果】尽管理论预测扩散与定植性状间的权衡关系普遍存在，但在哈氏 Townsendia中这一现象并未普遍出现。无融合生殖种子的终端速度（terminal velocity，即下落时在空中停留的时间更长）低于有性种子，且萌发成功率更高。尽管两类生殖类群的幼苗大小并无差异，但无融合生殖类群的幼苗存活率略低于有性类群。

【研究结论】上述早期生活史性状的差异，结合无融合生殖所赋予的生殖保障能力，表明无融合生殖类群可通过扩散与定植两方面的优势获得更广的分布范围。

【研究系统】哈氏 Townsendia是菊科（Asteraceae）的小型多年生植物，存在两种生殖型：进行有性生殖的二倍体，以及通过配子体无融合生殖（gametophytic apomixis）繁殖的同源多倍体（主要为三倍体）（Beaman, 1957；Thompson & Whitton, 2006）。有性生殖个体为自交不亲和，而无融合生殖类群可自主结种，无需花粉为胚乳受精。哈氏 Townsendia产生单粒种子的传播体（diaspore），带有持久的羽毛状冠毛（pappus）（Strother, 1993），通常依靠风力传播（Andersen, 1992）。尽管两类生殖型在倍性与生殖方式上存在差异，但在野外无法通过宏观形态进行区分，仅可通过花粉性状加以鉴别。多倍体产生的花粉粒比二倍体更大且具有活力，但其花粉活力显著更低。截至目前，本课题组已对该物种全分布范围内的90余个种群进行了性状鉴定，发现低花粉活力与大基因组尺寸间存在紧密关联（Thompson & Whitton, 2006；Garani, 2014；Lee, 2015），这一结果支持Beaman（1957）提出的“二倍体为有性生殖类群，多倍体为无融合生殖类群”的观点（Thompson & Whitton, 2006；Thompson et al., 2008）。有性生殖种群的分布范围远小于无融合生殖种群，主要分布于美国科罗拉多州博尔德市与怀俄明州拉勒米市之间（Lee, 2015）。无融合生殖种群的分布范围从怀俄明州南部沿落基山脉东侧向北延伸至加拿大不列颠哥伦比亚省。此外，在育空地区存在少量间断分布的二倍体有性与多倍体无融合生殖种群（Thompson & Whitton, 2006；Garani, 2014）。

【种子扩散性状与终端速度测定及分析】本研究以2008年至2013年间采集的传播体为材料，比较了无融合生殖类群与有性类群的传播体性状。样本严格来说为连萼瘦果（cypselae），下文统称“种子”，采集自哈氏 Townsendia全分布范围内的5个二倍体有性种群与7个多倍体无融合生殖种群，包括不列颠哥伦比亚省与育空地区的北部种群（附录S1、表S1；详见本文附属数据）。每个种群最多选取10株母株，每株选取2粒种子，仅选用饱满、颜色深暗（代表具有活力的性状；Garani, 2014）且冠毛完整的种子。为使冠毛恢复至相对舒展的状态（相较于收藏信封储存导致的略微扁平状态），我们将种子置于密封培养皿中的湿润滤纸上静置约24小时，随后取出并自然风干24小时。处理完成后，冠毛形态将更为规整，与野外采集时的状态一致。针对每粒种子，我们使用分析天平（analytical balance）测定其质量，记录冠毛的纤毛数量，并使用目镜测微尺（ocular micrometer）测量来自冠毛中央顶端的两根纤毛的长度。我们使用量角器测量攻角（即冠毛纤毛展开后以其与种子连接点为中心的最大夹角）（详见O’Connell与Eckert, 2001的图2，该图展示了传播体的相关性状）。我们通过将单粒种子从长120cm的透明亚克力玻璃管（acrylic glass tube）中落下的方式估算终端速度。测定时用镊子夹住冠毛，随后……