Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy.
Institute of Biosciences and BioResources (IBBR), National Research Council (CNR), Sesto Fiorentino (Firenze), Italy.
Ann Bot. 2019 Nov 15;124(5):849-860. doi: 10.1093/aob/mcz129.
At the rear edge of the distribution of species, extreme isolation and small population size influence the genetic diversity and differentiation of plant populations. This may be particularly true for Arctic-alpine species in mid-latitude mountains, but exactly how peripherality has shaped their genetic and reproductive characteristics is poorly investigated. The present study, focused on Salix herbacea, aims at providing new insights into the causes behind ongoing demographic dynamics and their consequences for peripheral populations of Arctic-alpine species.
We performed a whole-population, highly detailed sampling of the only two S. herbacea populations in the northern Apennines, comparing their clonal and genetic diversity, sex ratio and spatial genetic structure with a reference population from the Alps. After inspecting ~1800 grid intersections in the three populations, 563 ramets were genotyped at 11 nuclear microsatellite markers (nSSRs). Past demography and mating patterns of Apennine populations were investigated to elucidate the possible causes of altered reproductive dynamics.
Apennine populations, which experienced a Holocene bottleneck and are highly differentiated (FST = 0.15), had lower clonal and genetic diversity compared with the alpine population (RMLG = 1 and HE = 0.71), with the smaller population exhibiting the lowest diversity (RMLG = 0.03 and HE = 0.24). An unbalanced sex ratio was found in the larger (63 F:37 M) and the smaller (99 F:1 M) Apennine population. Both were characterized by the presence of extremely large clones (up to 2500 m2), which, however, did not play a dominant role in local reproductive dynamics.
Under conditions of extreme isolation and progressive size reduction, S. herbacea has experienced an alteration of genetic characteristics produced by the prevalence of clonal growth over sexual reproduction. However, our results showed that the larger Apennine population has maintained levels of sexual reproduction enough to counteract a dramatic loss of genetic and clonal diversity.
在物种分布的边缘，极端的隔离和小种群规模会影响植物种群的遗传多样性和分化。对于中纬度山脉的北极高山物种来说，这可能尤其如此，但外围环境究竟如何塑造了它们的遗传和繁殖特征，还没有得到很好的研究。本研究以柳属草本植物（Salix herbacea）为研究对象，旨在深入了解持续的种群动态背后的原因及其对北极高山物种边缘种群的影响。
我们对北阿平宁山脉仅有的两个柳属草本植物种群进行了全种群、详细的采样，将它们的克隆和遗传多样性、性别比例和空间遗传结构与阿尔卑斯山的参考种群进行了比较。在对三个种群的约 1800 个网格交点进行检查后，用 11 个核微卫星标记（nSSR）对 563 个克隆体进行了基因型分析。研究了阿平宁山脉种群的过去种群动态和交配模式，以阐明改变繁殖动态的可能原因。
经历了全新世瓶颈期且高度分化（FST = 0.15）的阿平宁山脉种群与高山种群相比，克隆和遗传多样性较低（RMLG = 1，HE = 0.71），其中较小的种群多样性最低（RMLG = 0.03，HE = 0.24）。较大（63 雌：37 雄）和较小（99 雌：1 雄）的阿平宁山脉种群的性别比例失衡。两个种群都有非常大的克隆体（最大可达 2500 m2），但它们在当地的繁殖动态中并没有占主导地位。
在极端隔离和逐渐缩小的条件下，柳属草本植物经历了遗传特征的改变，表现为克隆生长对有性繁殖的优势。然而，我们的研究结果表明，较大的阿平宁山脉种群维持了足够的有性繁殖水平，以抵消遗传和克隆多样性的急剧丧失。
