Odee David W, Wilson Julia, Omondi Stephen, Perry Annika, Cavers Stephen
Kenya Forestry Research Institute, PO Box 20412-00200, Nairobi, Kenya Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, UK
Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, UK.
AoB Plants. 2015 Feb 13;7:plv011. doi: 10.1093/aobpla/plv011.
Knowledge of rangewide variation in DNA content and ploidy level may be valuable in understanding the evolutionary history of a species. Recent studies of Acacia senegal report diploids and occasional tetraploids in the Sudano-Sahelian region of sub-Saharan Africa, but nothing is known about the overall extent of DNA ploidy variation within the species. In this study, we determine the DNA content and ploidy level of A. senegal across its native range, and explore whether the variation is related to its evolutionary and colonization history. We used propidium iodide flow cytometry (FCM) to estimate DNA content (2C value) and infer ploidy in 157 individuals from 54 populations on various tissues, using seeds, fresh leaves, dried leaves and twigs and herbarium specimens. The mean 2C DNA (pg ± s.d.) contents detected were 1.47 ± 0.09, 2.12 ± 0.02, 2.89 ± 0.12, and a single individual with 4.51 pg, corresponding to a polyploid series of diploid, triploid, tetraploid and hexaploid individuals. Diploids were confirmed by chromosome counts (2n = 2x = 26). Most populations (90.7 %) were of single ploidy level, while mixed ploidy populations (9.3 %) comprising mostly diploids (2x+3x, 2x+4x and 2x+6x) were restricted to the Sudano-Sahelian and Indian subcontinent regions, its northern range. The species is predominantly diploid, and no mixed ploidy populations were detected in east and southern Africa, its southern range. The geographic pattern of ploidy variation in conjunction with existing phylogeographic and phylogenetic data of the species suggests that polyploids have occurred multiple times in its evolutionary and recent colonization history, including contemporary ecological timescales. The successful use of external tissues of dried twigs in FCM is new, and presents the opportunity to study numerous other dryland woody species.
了解物种DNA含量和倍性水平的全范围变异，对于理解一个物种的进化历史可能具有重要价值。最近对塞内加尔金合欢的研究报告称，在撒哈拉以南非洲的苏丹-萨赫勒地区存在二倍体以及偶尔出现的四倍体，但对于该物种内DNA倍性变异的整体范围尚无了解。在本研究中，我们测定了塞内加尔金合欢在其原生范围内的DNA含量和倍性水平，并探讨这种变异是否与其进化和殖民历史相关。我们使用碘化丙啶流式细胞术（FCM）来估计DNA含量（2C值），并推断来自54个种群的157个个体在各种组织（种子、新鲜叶片、干燥叶片、嫩枝和标本馆标本）中的倍性。检测到的平均2C DNA（pg±标准差）含量分别为1.47±0.09、2.12±0.02、2.89±0.12，以及一个含量为4.51 pg的个体，分别对应二倍体、三倍体、四倍体和六倍体个体的多倍体系列。通过染色体计数（2n = 2x = 26）证实了二倍体。大多数种群（90.7%）处于单一倍性水平，而主要由二倍体组成的混合倍性种群（9.3%）（2x + 3x、2x + 4x和2x + 6x）仅限于其北部范围的苏丹-萨赫勒和印度次大陆地区。该物种主要为二倍体，在其南部范围的东非和南非未检测到混合倍性种群。倍性变异的地理模式与该物种现有的系统地理学和系统发育数据表明，多倍体在其进化和近期殖民历史中多次出现，包括当代生态时间尺度。在FCM中成功使用干燥嫩枝的外部组织是新的方法，为研究许多其他旱地木本物种提供了机会。
