偏花报春和海仙报春3个同域居群的不对称杂交

Asymmetric hybridization of Primula secundiflora and P. poissonii in three sympatric populations

自然杂交是进化生物学研究中的热点,而杂交方向则是理解自然杂交和生殖隔离机制的一个关键环节。偏花报春(Primula secundifora)和海仙报春(P.poissonii)在横断山区重叠分布且存在自然杂交现象,研究仅证实了种间杂交的发生,但对不同地域的这2个物种间的杂交方向并未开展深入研究。本研究选取偏花报春和海仙报春3个同域分布点的居群,利用双亲遗传的核转录间隔区ITS和母系遗传的叶绿体片段trnH-psb A构建系统树,检测了3个居群中的自然杂交以及杂交方向;通过人工授粉实验检测种内种间杂交以及不同物种作为母本时对结籽数的影响水平。DNA分子标记结果显示每个居群中的杂交方向都是不对称的,海仙报春更容易在杂交中作为母本。人工授粉的结果表明种内种间交配以及哪个种作为母本对结籽数有非常显著的影响。海仙报春作为母本时能够显著提高结籽数。这2个物种之间不同的生殖隔离强度可能是造成不对称杂交的原因。3个居群中都是以海仙报春更易作母本,可能是因为这3个地点的种间生殖隔离具有相似的机制。

Natural hybridization is one of the research hotspots in evolutionary biology. The direction of hybridization is a critical aspect to understanding natural hybridization and interspecific reproductive isolation. Although natural hybridization between Primula secundiflora and P. poissonii has been confirmed in overlapping areas in the Hengduan Mountains, the interspecific hybridization directions among different populations remain unclear. We chose three sympatric populations to test interspecific hybridization directions. Biparentally inherited nuclear internal transcribed spacer （ITS） and maternally inherited chloroplast sequence trnH-psbA techniques were used to confirm hybridization and to test directions. Moreover, hand pollination of intraspecies and interspecies populations were performed to detect which factors influence seed numbers and hybridization patterns. Results of DNA marker analysis suggested that the direction of hybridization was asymmetric in each population, and P poissonii was found to be the most maternal parent. Intraspecific crossing produced significantly more seeds than interspecific crossing. Primula poissonii produced significantly higher seed numbers when it was treated as the maternal parent. The asymmetric direction may be the result of the asymmetric strength of reproductive barriers between P secundiflora and P. poissonff. Similar mechanisms of reproductive isolation may contribute to the asymmetric hybridization among the three sympatric sites.