Department of Systematics, Biodiversity and Evolution of Plants, Albrecht-von-Haller Institute for Plant Sciences, University of Goettingen, Untere Karspuele, Goettingen, Germany.
Instituto de Botánica del Nordeste (IBONE), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (FCA-UNNE), Corrientes, Argentina.
Ann Bot. 2018 May 11;121(6):1183-1196. doi: 10.1093/aob/mcy004.
Niche divergence between polyploids and their lower ploidy progenitors is one of the primary mechanisms fostering polyploid establishment and adaptive divergence. However, within-species chromosomal and reproductive variability have usually been neglected in community ecology and biodiversity analyses even though they have been recognized to play a role in the adaptive diversification of lineages.
We used Paspalum intermedium, a grass species with diverging genetic systems (diploidy vs. autopolyploidy, allogamy vs. autogamy and sexuality vs. apomixis), to recognize the causality of biogeographic patterns, adaptation and ecological flexibility of cytotypes. Chromosome counts and flow cytometry were used to characterize within-species genetic systems diversity. Environmental niche modelling was used to evaluate intraspecific ecological attributes associated with environmental and climatic factors and to assess correlations among ploidy, reproductive modes and ecological conditions ruling species' population dynamics, range expansion, adaptation and evolutionary history.
Two dominant cytotypes non-randomly distributed along local and regional geographical scales displayed niche differentiation, a directional shift in niche optima and signs of disruptive selection on ploidy-related ecological aptitudes for the exploitation of environmental resources. Ecologically specialized allogamous sexual diploids were found in northern areas associated with higher temperature, humidity and productivity, while generalist autogamous apomictic tetraploids occurred in southern areas, occupying colder and less productive environments. Four localities with a documented shift in ploidy and four mixed populations in a zone of ecological transition revealed an uneven replacement between cytotypes.
Polyploidy and contrasting reproductive traits between cytotypes have promoted shifts in niche optima, and increased ecological tolerance and niche divergence. Ecologically specialized diploids maintain cytotype stability in core areas by displacing tetraploids, while broader ecological preferences and a shift from sexuality to apomixis favoured polyploid colonization in peripheral areas where diploids are displaced, and fostered the ecological opportunity for autotetraploids supporting range expansion to open southern habitats.
多倍体与其低倍体祖先之间的生态位分化是促进多倍体建立和适应性分化的主要机制之一。然而，即使已经认识到染色体和生殖多样性在谱系的适应性多样化中发挥作用，但在群落生态学和生物多样性分析中，种内染色体和生殖多样性通常被忽视。
我们使用具有不同遗传系统（二倍体与同源多倍体、异交与自交、有性与无融合生殖）的中间雀稗（Paspalum intermedium）来识别生物地理格局、适应和生态型弹性的因果关系。染色体计数和流式细胞术用于描述种内遗传系统多样性。环境生态位模型用于评估与环境和气候因素相关的种内生态特征，并评估多倍体、生殖方式与决定物种种群动态、分布范围扩张、适应和进化历史的生态条件之间的相关性。
两个主要的细胞学类型在局部和区域地理尺度上呈非随机分布，表现出生态位分化、生态位最优值的定向变化以及与多倍体相关的生态适应性的不连续选择迹象。在与较高温度、湿度和生产力相关的北部地区发现了生态特化的异交有性二倍体，而在较冷和生产力较低的南部地区则出现了一般化的自交无融合生殖四倍体。在四个有记录的多倍体转变的地点和一个生态过渡带的四个混合种群中，细胞学类型之间存在不平衡的替代。
多倍体和细胞学类型之间的对比生殖特征促进了生态位最优值的变化，并提高了生态耐受性和生态位分化。生态特化的二倍体通过排挤四倍体来维持核心区域的细胞学稳定性，而更广泛的生态偏好和从有性到无融合生殖的转变则有利于多倍体在被排挤的外围地区的殖民化，并为支持分布范围扩张到开阔的南部栖息地的自交四倍体提供了生态机会。
