The natural hybridization that occurs between two sympatric species of Rhododendron subgenus Hymenanthes in Yunnan, China, was investigated. In field observations, it was noted that the putative hybrids between R. delavayi Franch. and R. cyanocarpum （Franch.） Franch. ex W.W. Sm. had intermediate morphologies. On the basis of morphology, chloroplast DNA （trnL-rp132） and nuclear DNA （waxy）, hybrids and parental species were identified. Hybridization occurred in both directions, but was asymmetrical, with R. delavayi as the major maternal parent. Reciprocal hand pollination treatments showed that either species, as pollen donor or pollen receiver, could produce fruits. It was noted that fruit set varied among treatments. The same pollinators （bumblebees） were shared in both parental species. From these results, we conclude that individuals with intermediate morphologies are indeed of hybrid origin from natural hybridization between R. cyanocarpum and R. delavayi. Furthermore, we presume the hybridization at the study site could have been initiated by habitat disturbance in the 1950s, and we may hence witness the early stages of hybrid swarm formation.
Yong-Peng MaChang-Qin ZhangJing-Li ZhangJun-Bo Yang
The levels and partitioning of genetic diversity and inbreeding depression were investigated in Tupistra pingbianensis, a narrow endemic of southeast Yunnan, China, characterized by a naturally fragmented distribution due to extreme specialization on a rare habitat type. Here genetic diversity and patterns of genetic variation within and among 11 populations were analyzed using amplified fragment length polymorphism markers with 97 individuals across its whole geographical range. High levels of genetic variation were revealed both at the species level （P99 = 96.012%; Ht = 0.302） and at the population level （P99= 51.41%; Hs = 0.224）. Strong genetic differentiation among populations was also detected （FsT= 0.2961; 011 = 0.281）, which corresponded to results reported for typical animal-pollinated, mixed selfing, and outcrossing plant species. This result was consistent with mating patterns detected by our pollination experiments. The indirect estimate of gene flow based on OII was low （Nm = 0.64）. Special habitat and its life history traits might play an important role in shaping the genetic diversity and the genetic structure of this species. A pollination experiment also failed to detect significant inbreeding depression upon F1 fruit set, seed weight, and germinate rate fitness-traits. As a naturally rare species, T. pingbianensis is not seriously genetically impoverished and likely to have adapted to tolerating a high level of inbreeding early in its history, we propose this species need only periodic monitoring to ensure their continued persistence, but not intervention to remain viable.
