Gutiérrez-Flores Carina, la Luz José L León-de, León Francisco J García-De, Cota-Sánchez J Hugo
Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK, S7N5E2, Canada.
HICB Herbarium, Centro de Investigaciones Biológicas del Noroeste, Instituto Politécnico Nacional 195, Playa Palo de Santa Rita Sur, C.P. 23096, La Paz, B.C.S., México.
Comp Cytogenet. 2018 Feb 14;12(1):61-82. doi: 10.3897/CompCytogen.v12i1.21554. eCollection 2018.
Polyploidy, the possession of more than two sets of chromosomes, is a major biological process affecting plant evolution and diversification. In the Cactaceae, genome doubling has also been associated with reproductive isolation, changes in breeding systems, colonization ability, and speciation. (S. Watson, 1885) Britton & Rose, 1909, is a columnar cactus that has long drawn the attention of ecologists, geneticists, and systematists due to its wide distribution range and remarkable assortment of breeding systems in the Mexican Sonoran Desert and the Baja California Peninsula (BCP). However, several important evolutionary questions, such as the distribution of chromosome numbers and whether the diploid condition is dominant over a potential polyploid condition driving the evolution and diversity in floral morphology and breeding systems in this cactus, are still unclear. In this study, we determined chromosome numbers in 11 localities encompassing virtually the entire geographic range of distribution of . Our data revealed the first diploid (2n = 22) count in this species restricted to the hermaphroditic populations of Catalana (ICA) and Cerralvo (ICE) Islands, whereas the tetraploid (2n = 44) condition is consistently distributed throughout the BCP and mainland Sonora populations distinguished by a non-hermaphroditic breeding system. These results validate a wider distribution of polyploid relative to diploid individuals and a shift in breeding systems coupled with polyploidisation. Considering that the diploid base number and hermaphroditism are the proposed ancestral conditions in Cactaceae, we suggest that ICE and ICA populations represent the relicts of a southern diploid ancestor from which both polyploidy and unisexuality evolved in mainland BCP, facilitating the northward expansion of this species. This cytogeographic distribution in conjunction with differences in floral attributes suggests the distinction of the diploid populations as a new taxonomic entity. We suggest that chromosome doubling in conjunction with allopatric distribution, differences in neutral genetic variation, floral traits, and breeding systems has driven the reproductive isolation, evolution, and diversification of this columnar cactus.
多倍体，即拥有两套以上染色体，是影响植物进化和多样化的一个主要生物学过程。在仙人掌科中，基因组加倍还与生殖隔离、繁殖系统变化、定殖能力和物种形成有关。（S. 沃森，1885年）布里顿和罗斯，1909年，是一种柱状仙人掌，因其广泛的分布范围以及在墨西哥索诺拉沙漠和下加利福尼亚半岛（BCP）显著多样的繁殖系统，长期以来一直吸引着生态学家、遗传学家和分类学家的关注。然而，一些重要的进化问题，如染色体数目的分布以及二倍体状态是否在驱动该仙人掌花形态和繁殖系统进化与多样性的潜在多倍体状态中占主导地位，仍然不清楚。在本研究中，我们确定了涵盖几乎整个地理分布范围的11个地点的染色体数目。我们的数据揭示了该物种首次出现的二倍体（2n = 22）计数，仅限于卡塔拉纳（ICA）和塞拉尔沃（ICE）岛的雌雄同体种群，而四倍体（2n = 44）状态则始终分布在整个BCP以及以非雌雄同体繁殖系统为特征的索诺拉大陆种群中。这些结果证实了相对于二倍体个体，多倍体的分布更广泛，以及繁殖系统与多倍体化相关的转变。鉴于二倍体基数和雌雄同体被认为是仙人掌科的原始状态，我们认为ICE和ICA种群代表了一个南方二倍体祖先的遗迹，在BCP大陆上，多倍体和单性花都从这个祖先进化而来，促进了该物种向北扩张。这种细胞地理分布以及花特征的差异表明，二倍体种群可作为一个新的分类实体加以区分。我们认为，染色体加倍与异域分布、中性遗传变异差异、花性状和繁殖系统共同推动了这种柱状仙人掌的生殖隔离、进化和多样化。
