Kunming Botanic Garden, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan, China.
Am J Bot. 2010 Oct;97(10):1749-57. doi: 10.3732/ajb.1000018. Epub 2010 Sep 9.
One potential threat to rare species is genetic swamping caused by hybridization, but few studies have quantified this threat. Rhododendron cyanocarpum is a narrow endemic species that occurs sympatrically with potentially interfertile congeners throughout its range within Yunnan, China. We searched the entire distribution of R. cyanocarpum for hybrids and examined the patterns of hybridization to assess potential threat from hybridization. •
In a comprehensive field survey, we detected only one instance of hybridization involving R. cyanocarpum, with R. delavayi, at Huadianba near Dali. Material of both species and putative hybrids was examined using morphology, chloroplast DNA, nuclear ribosomal DNA, and Bayesian analysis of AFLP profiles. •
Of 10 putative hybrids, two were F(1)(')s and at least seven were F(2)(')s. Four backcrosses to R. delavayi were detected among material with R. delavayi-like morphology within the hybrid zone. Backcrosses to R. cyanocarpum were not detected. Therefore F(2)(')s outnumbered all other classes within the hybrid zone, a situation not previously confirmed for plants and extremely rare generally. Hybridization was asymmetrical, with R. delavayi as the maternal parent in all but one of the hybrids detected. •
Although natural hybridization is common in Rhododendron, it is rare in R. cyanocarpum and is apparently not accompanied by backcrossing toward R. cyanocarpum. Hence, there is no immediate risk of genetic swamping, unless habitat disturbance increases and changes the patterns of hybridization. Our study is the first to report a plant hybrid zone dominated by F(2) hybrids. This pattern might contribute to species barrier maintenance.
杂交导致的遗传淹没是稀有物种的潜在威胁之一，但很少有研究量化这种威胁。马缨杜鹃是一种狭窄的特有种，在中国云南境内与其潜在可杂交的同属物种发生同域分布。我们在马缨杜鹃的整个分布区内搜索了杂交种，并研究了杂交模式，以评估杂交造成的潜在威胁。
在全面的野外调查中，我们仅在大理附近的华甸坝发现了一个涉及马缨杜鹃和马缨杜鹃的杂交种实例。利用形态学、叶绿体 DNA、核核糖体 DNA 和 AFLP 图谱的贝叶斯分析，对两个物种和可能的杂种材料进行了检查。
在 10 个可能的杂种中，有 2 个是 F(1)杂种，至少有 7 个是 F(2)杂种。在杂交区中，有 4 个材料与马缨杜鹃形态相似，检测到马缨杜鹃的回交。未检测到回交到马缨杜鹃的情况。因此，F(2)杂种在杂交区内的数量超过了所有其他类群，这种情况在植物中以前没有被证实过，在一般情况下也极为罕见。杂交是不对称的，在所检测到的杂种中，除了一个外，马缨杜鹃都是母本。
尽管在杜鹃属中天然杂交很常见，但在马缨杜鹃中却很少见，而且显然没有与回交到马缨杜鹃的情况相伴。因此，除非栖息地受到干扰增加并改变了杂交模式，否则不会有遗传淹没的直接风险。我们的研究首次报道了一个以 F(2)杂种为主的植物杂交区。这种模式可能有助于维持物种间的障碍。
