Department of Ecology and Evolutionary Biology, 25 Willcocks Street, University of Toronto, Toronto, ON, Canada.
Department of Biology, 116 Barrie St., Biosciences Complex, Queen's University, Kingston, ONCanada.
Ann Bot. 2022 Jul 19;130(1):27-40. doi: 10.1093/aob/mcac056.
Reproductive systems enabling opportunities for self-fertilization influence population genetic structure and play a key role in colonization and genetic differentiation during range expansion. Because of their well-developed powers of dispersal, aquatic plants often have widespread disjunct geographical distributions, providing opportunities to investigate the role of reproductive systems in structuring genetic variation between parts of the range that differ in migration history and ecology.
We compared reproductive systems and spatial genetic structure of the freshwater aquatic macrophyte Sagittaria latifolia between disjunct western and eastern ranges of North America (NA). Populations of this species are most commonly either monoecious or dioecious. We examined chloroplast DNA haplotype variation to test the hypothesis that the western range of this species represents a secondary colonization from the east, and evaluated the roles of reproductive system differences and geography in structuring contemporary patterns of genetic variation at 11 polymorphic SSR (simple sequence repeat) loci.
Chloroplast haplotyping revealed a single haplotype in western NA compared to numerous haplotypes in eastern NA, consistent with a genetic bottleneck during westward migration. Estimates of genetic diversity in eastern NA populations differed significantly between reproductive systems, but this pattern was not evident in the western range. Eastern populations could be reliably assigned to genetic clusters based on their reproductive systems, whereas western populations clustered primarily by geographical location.
The sparser distribution of aquatic habitats in the drier western range of S. latifolia, combined with secondary colonization of this region, probably cause the lower genetic diversity and increased differentiation among populations, possibly overriding the effects of reproductive system evident in the eastern portion of the range. Our findings demonstrate that the complex interplay between migratory history, reproductive systems and habitat availability plays an important role in structuring spatial patterns of genetic variation in disjunct plant populations.
具有自体受精能力的生殖系统会影响种群遗传结构，并在范围扩张过程中的殖民和遗传分化中发挥关键作用。由于水生植物具有发达的扩散能力，它们通常具有广泛的地理间断分布，为研究生殖系统在构建遗传变异方面的作用提供了机会，这些遗传变异存在于范围的不同部分，这些部分在迁移历史和生态方面存在差异。
我们比较了北美（NA）东西部分散的淡水水生植物箭叶泽泻（Sagittaria latifolia）的生殖系统和空间遗传结构。该物种的种群通常是雌雄同体或雌雄异株。我们检查了叶绿体 DNA 单倍型变异，以检验该物种的西部种群代表从东部二次殖民的假说，并评估了生殖系统差异和地理因素在构建 11 个多态性 SSR（简单序列重复）位点的当代遗传变异模式中的作用。
叶绿体单倍型分析显示，与东部 NA 的众多单倍型相比，西部 NA 只有一个单倍型，这与向西迁移过程中的遗传瓶颈一致。东部 NA 种群的遗传多样性估计值在生殖系统之间存在显著差异，但在西部范围则不然。东部种群可以根据其生殖系统可靠地分配到遗传聚类中，而西部种群则主要根据地理位置聚类。
在较为干燥的西部，水生生境的分布较为稀疏，再加上该地区的二次殖民，可能导致种群遗传多样性降低，种群间分化增加，这可能会掩盖生殖系统在东部范围的影响。我们的研究结果表明，迁移历史、生殖系统和栖息地可获得性之间的复杂相互作用，在构建间断植物种群的遗传变异空间格局方面发挥着重要作用。
