Department of Biology, Duke University, Box 90338, Durham, North Carolina, 27708, USA.
University and Jepson Herbaria and Department of Integrative Biology, University of California, Berkeley, California, 94720, USA.
Am J Bot. 2018 Dec;105(12):2051-2064. doi: 10.1002/ajb2.1201. Epub 2018 Dec 13.
Ecological differentiation (ED) between sexual and asexual organisms may permit the maintenance of reproductive polymorphism. Several studies of sexual/asexual ED in plants have shown that the geographic ranges of asexuals extend beyond those of sexuals, often in areas of higher latitude or elevation. But very little is known about ED at fine scales, wherein coexistence of sexuals and asexuals may be permitted by differential niche occupation.
We used 149 populations of sexual and apomictic lineages in the genus Boechera (rock cress) collected across a portion of this mustard's vast range. We characterized reproductive mode, ploidy, and species identity or hybrid parentage of each individual, and then used a multipronged statistical approach to (1) identify ED between sexuals and asexuals; (2) investigate the impacts of two confounding factors, polyploidy and hybridization, on ED; and (3) determine the environmental variables underlying ED.
We found that sexuals and asexuals are significantly ecologically differentiated across the landscape, despite fine-scale interdigitation of these two reproductive forms. Asexual reproduction was strongly associated with greater disturbance, reduced slope, and greater environmental variability. Although ploidy had little effect on the patterns observed, hybridization has a unique impact on the relationships between asexual reproduction and specific environmental variables.
Ecological differentiation along the axes of disturbance, slope, and climatic variability, as well as the effects of heterozygosity, may contribute to the maintenance of sexuality and asexuality across the landscape, ultimately impacting the establishment and spread of asexual lineages.
有性和无性生物之间的生态分化（ED）可能允许生殖多态性的维持。对植物有性/无性 ED 的几项研究表明，无性生物的地理范围超出了有性生物的范围，通常在更高纬度或海拔的地区。但是，对于精细尺度上的 ED 知之甚少，在精细尺度上，有性生物和无性生物可能通过差异生态位占据而共存。
我们使用了在 Boechera 属（岩芥）的一部分广泛分布范围内收集的 149 个有性和无融合生殖谱系的种群。我们描述了每个个体的生殖模式、倍性和物种身份或杂种亲本，然后使用多管齐下的统计方法来（1）识别有性生物和无性生物之间的 ED；（2）研究多倍体和杂交这两个混杂因素对 ED 的影响；（3）确定 ED 的环境变量。
尽管这两种生殖形式在微观尺度上相互交织，但我们发现有性生物和无性生物在景观上存在明显的生态分化。无性繁殖与更大的干扰、更小的坡度和更大的环境变异性强烈相关。虽然倍性对观察到的模式影响不大，但杂交对无性繁殖与特定环境变量之间的关系有独特的影响。
沿着干扰、坡度和气候变异性的轴的生态分化，以及杂合性的影响，可能有助于在景观上维持有性和无性生殖，最终影响无性谱系的建立和传播。
