Data from: Widespread generalist clones are associated with range and niche expansion in allopolyploids of Pacific Northwest Hawthorns (Crataegus L.)

Range and niche expansion are commonly associated with transitions to asexuality, polyploidy, and hybridity (allopolyploidy) in plants. The ability of asexual polyploids to colonize novel habitats may be due to widespread generalist clones, multiple ecologically specialized clones, or may be a neutral byproduct of multiple, independent origins of asexual polyploids throughout the range. We have quantified niche size and divergence for hawthorns of the Pacific Northwest using data from herbarium vouchers with known cytotypes. We find that all polyploid niches diverge from that of the diploid range, and allopolyploids have the broadest niches. Allotetraploids have the largest niche and the widest geographic distribution. We then assessed the genetic mechanism of range expansion by surveying the ecological and geographic distribution of genotypes within each cytotype from sites in which fine-scale habitat assessments were completed. We find no isolation by either geographic or ecological distance in allopolyploids, suggesting high dispersal and colonization ability. In contrast, autotriploids and diploids show patterns of isolation by geographic distance. We also compared the geographic and ecological distributions of clonal genotypes with those of randomly drawn sites of the most widespread cytotype. We found that most clones are geographically widespread and occur in a variety of habitats. We interpret these findings to suggest that patterns of range and niche expansion in Pacific Northwest Hawthorns may stem from these widespread, ecologically generalist clones of hybrid origin.

植物的分布范围扩张与生态位拓展，通常与向无性生殖、多倍体以及杂交性（异源多倍性，allopolyploidy）的演化转变密切相关。无性生殖多倍体开拓新生境的能力，可能源于广泛分布的泛化克隆、多种生态特化克隆，或是整个分布区内多次独立起源的无性多倍体所产生的中性副产物。本研究借助已知细胞型（cytotype）的标本馆凭证标本数据，对北美太平洋西北地区山楂属植物的生态位大小与分化程度展开了量化分析。研究结果显示，所有多倍体的生态位均与二倍体的分布生态位产生分化，而异源多倍体的生态位最为宽泛。异源四倍体（allotetraploid）拥有最大的生态位与最广泛的地理分布范围。随后，本研究通过对完成精细生境评估的样点中各细胞型内的基因型（genotype）的生态与地理分布开展调查，解析了范围扩张的遗传机制。我们发现异源多倍体未出现由地理距离或生态距离介导的遗传隔离，这表明其具备极强的扩散与定植能力。与之相对，同源三倍体（autotriploid）与二倍体则呈现出由地理距离导致的遗传隔离模式。此外，本研究还将克隆基因型的地理与生态分布，与随机选取的分布最广的细胞型样点分布进行了对比。结果表明，绝大多数克隆在地理上广泛分布，且可栖息于多种生境之中。综上，我们认为北美太平洋西北地区山楂属植物的范围扩张与生态位拓展模式，可能正是源于这些起源于杂交事件、广泛分布且具备生态泛化性的克隆。