Instituto de Genética e Bioquímica, Universidade Federal de Uberlândia, Uberlândia, Brazil.
Instituto de Biologia, Universidade Federal de Uberlândia, Uberlândia, Brazil.
Plant Biol (Stuttg). 2021 Jan;23(1):91-99. doi: 10.1111/plb.13177. Epub 2020 Dec 6.
Geographic parthenogenesis, range expansion of apomictic plants after climate changes, has been described for Northern Hemisphere gametophytic apomicts. But similar trends have been observed for sporophytic apomicts of Cerrado, the savannas in Brazil. Eriotheca pubescens is a common Cerrado tree, an agamic complex of either hexaploid/polyembryonic apomicts or tetraploid/monoembryonic sexual individuals. Some populations have been described as a new species, Eriotheca estevesiae, all included in the Eriotheca Stellate Trichome Species Complex (ESTSC). Since breeding systems and ploidy are clearly associated with polyembryony and stomatal size, we used these ancillary features to map the reproductive and ploidy level traits of E. pubescens and E. estevesiae. Leaves and seeds were collected from individuals of 19 populations. Seeds were evaluated for the presence of polyembryony and leaves for stomatal measurements. Eight populations were monoembryonic while another eight were polyembryonic and for other three, the embryonic pattern was not readily verified. E. pubescens polyembryonic and hexaploid populations formed a homogeneous group, but monoembryonic plants were more variable. E. estevesiae populations were monoembryonic with smaller stomata. In contrast, some E. pubescens monoembryonic populations further south presented larger stomata. Despite these outliers, possibly mixed populations, stomatal size and embryonic pattern differed from northern to southern populations. Embryonic pattern and stomatal size indicated that northernmost populations of Eriotheca STSC (E. estevesiae) are diploid and sexual. Southernmost populations, mostly polyembryonic and with large stomata, are hexaploid and apomictic. This is in agreement with geographic parthenogenesis and range expansion of apomictic lineages to southern habitats available after the last glacial maximum.
地理上的孤雌生殖，即在气候变化后无融合生殖植物的分布范围扩大，在北半球的配子体无融合生殖植物中已有描述。但在巴西的塞拉多（Cerrado），即热带稀树草原的孢子体无融合生殖植物中也观察到了类似的趋势。Eriotheca pubescens 是一种常见的塞拉多树种，是六倍体/多胚的无融合生殖或四倍体/单胚的有性个体的无融合生殖复合体。一些种群被描述为一个新物种，Eriotheca estevesiae，都包含在 Eriotheca Stellate Trichome Species Complex（ESTSC）中。由于繁殖系统和倍性显然与多胚性和气孔大小有关，我们使用这些辅助特征来绘制 E. pubescens 和 E. estevesiae 的生殖和倍性特征图谱。从 19 个种群的个体中收集了叶片和种子。评估种子是否有多胚性，叶片则用于测量气孔大小。八个种群是单胚的，而另外八个是多胚的，对于另外三个种群，胚胎模式不容易验证。E. pubescens 多胚和六倍体种群形成了一个同质群体，但单胚植物则更加多样化。E. estevesiae 种群是单胚的，气孔较小。相比之下，一些更靠南的 E. pubescens 单胚种群则具有更大的气孔。尽管存在这些异常值，可能是混合种群，但从北到南的种群，气孔大小和胚胎模式都存在差异。胚胎模式和气孔大小表明，Eriotheca STSC（E. estevesiae）最北部的种群是二倍体和有性的。最南部的种群，大多是多胚的，并且气孔较大，是六倍体和无融合生殖的。这与无融合生殖谱系在末次冰盛期后向南部栖息地的地理性孤雌生殖和分布范围扩大是一致的。
