Department of Botany, Natural History Museum, London SW7 5BD, UK.
Ann Bot. 2011 Jul;108(1):143-57. doi: 10.1093/aob/mcr118. Epub 2011 May 18.
Successful establishment of newly formed polyploid species depends on several interlinked genetic and ecological factors. These include genetic diversity within and among individuals, chromosome behaviour and fertility, novel phenotypes resulting from novel genomic make-up and expression, intercytotypic and interspecific competition, and adaptation to distinct habitats. The allotetraploid rock fern Asplenium majoricum is known from one small population in Valencia, Spain, and several larger populations on the Balearic island of Majorca. In Valencia, it occurs sympatrically with its diploid parents, A. fontanum subsp. fontanum and A. petrarchae subsp. bivalens, and their diploid hybrid A. × protomajoricum. This highly unusual situation allowed the study of polyploid genetic diversity and its relationship to the formation and establishment of nascent polyploid lineages.
Genetic variation for isozyme and chloroplast DNA markers was determined for A. majoricum and A. × protomajoricum sampled thoroughly from known sites in Majorca and Valencia. Results were compared with variation determined previously for the diploid parent taxa.
A highly dynamic system with recurring diploid hybrid and allotetraploid formation was discovered. High diversity in the small Valencian A. majoricum population indicates multiple de novo origins from diverse parental genotypes, but most of these lineages become extinct without becoming established. The populations on Majorca most probably represent colonization(s) from Valencia rather than an in situ origin. Low genetic diversity suggests that this colonization may have occurred only once.
There is a striking contrast in success of establishment of the Majorcan and Valencian populations of A. majoricum. Chance founding of populations in a habitat where neither A. fontanum subsp. fontanum nor A. petrarchae subsp. bivalens occurs appears to have been a key factor enabling the establishment of A. majoricum on Majorca. Successful establishment of this polyploid is probably dependent on geographic isolation from diploid progenitor competition.
新形成的多倍体物种的成功建立取决于几个相互关联的遗传和生态因素。这些因素包括个体内部和个体之间的遗传多样性、染色体行为和育性、新基因组构成和表达带来的新表型、细胞间和种间竞争，以及对不同生境的适应。异源四倍体岩蕨 Asplenium majoricum 仅见于西班牙巴伦西亚的一个小种群，以及马略卡岛的几个较大种群。在巴伦西亚，它与二倍体亲本 Asplenium fontanum subsp. fontanum 和 A. petrarchae subsp. bivalens 以及它们的二倍体杂种 A. × protomajoricum 同域分布。这种极不寻常的情况使得研究多倍体遗传多样性及其与新生多倍体谱系的形成和建立的关系成为可能。
对在马略卡岛和巴伦西亚的已知地点全面采样的 A. majoricum 和 A. × protomajoricum 进行同工酶和叶绿体 DNA 标记的遗传变异分析。结果与以前确定的二倍体亲代分类群的变异进行了比较。
发现了一个具有反复出现的二倍体杂种和异源四倍体形成的高度动态系统。在巴伦西亚的小 A. majoricum 种群中发现了高度的多样性，这表明它是由多种不同的亲本基因型多次从头起源的，但这些谱系中的大多数在没有建立起来之前就灭绝了。马略卡岛的种群很可能是从巴伦西亚殖民而来的，而不是原地起源的。低遗传多样性表明，这种殖民可能只发生过一次。
A. majoricum 在马略卡岛和巴伦西亚种群的建立成功率存在显著差异。在既没有 A. fontanum subsp. fontanum 也没有 A. petrarchae subsp. bivalens 出现的栖息地中偶然建立种群，似乎是 A. majoricum 在马略卡岛建立的关键因素。该多倍体的成功建立可能依赖于与二倍体祖先竞争的地理隔离。
