Phylogeographic Study Of Aquilegia Yabeana Complex Based On The Chloroplast DNA Markers

Flower is the reproductive organ which only appears in angiosperms. It is a notable innovation of the angiosperms, and has clearly played a major role in their diversification. Petals, the second whorl of flower organ which only appears in the eudicot. demonstrate great morphological variation, and is the major source of flower diversity. The function of petals is to attract pollinators, thus its evolution in angiosperms has been an important subject in the study of evolutionary biology. Aquilegia has emerged as a model system for the study of petals evolution, as its unusual floral organs such as petaloid sepals, the staminodium, and peatals with a nectar spur. Pollination studies of north American Aquilegia revealed that the evolution of nectar spur length was related to the adaptation of the plants to different pollinators. Whereas, there are populations, which belong to A. yabeana complex among Aquilegia taxa in China, whose nectar spur has stopped developing. There are four types of nectar spur in A. yabeana complex:curved, straight, slender and spurless. To explore the mechanism of the genesis of spurless trait, we must confirm the origin and the evolution history of the populations whose nectar spur has stopped developing at first. In this study we used data from three chloroplast fragments (rpl32-trnL, trnK-rps1 and rps16-trnQ) to study the phylogeography of a total of 285 individuals belonging to 56 populations in the A. yabeana complex. The main result and conclusion are as follows.1) The results of the phylogeny based on Maximun likelihood and Bayesion inference suggest that there are no correlation between the genetic differentiation and 4 different nectar spur status among the populations of A. yabeana complex. The topology structure of the phylogenetic tree composed of two clades:Clade 1 distributing in the second ladder and the north of third ladder of China, including populatinos in Shanxi, Henan, Hubei, north of Guizhou, Shanxi, Hebei, Beijing, west of Liaoning; and Clade 2 distributing in the first ladder, including populatinos in Yunan, Sichuan, Xizang, Gansu, Qinghai, west of Shanxi. The results of the phylogenetic analysis also showed that there was a process of rapid radiation in A. yabeana complex.2) Forty-two haplotypes were detected based on three chloroplast fragments. All of the forty-two haplotypes were separated into two Groups:Group 1 includes twenty-five haplotypes which distributed in the second ladder and the north of third ladder of China, and Group 2 includes seventeen haplotypes which distributed in the first ladder.3) The total genetic diversity among 56 populations (HT=0.956) was higher than the average of genetic diversity within population (Hs=0.290). It is suggested that the genetic diversity of A. yabeana complex was high. A strong phylogeographic pattern (nst>GsT, P<0.05) across the distribution range of A. yabeana complex was detected. AMOVA revealed that genetic variation occurred mainly among populations (FST =0.76038, P<0.05). The results of Mismatch distribution analysis and Neutrality test showed that there was a demographic expansion recently among these populations.4) The results of haplotype analysis suggest that the existence populations of A. yabeana complex derived from 3 glacial refugia during quaternary ice age, which were located in the north of Hengduan Mountains in the first ladder, the middle part of Qinling Mountains in the second ladder, the boundary between Hebei and Liaoning in the third ladder, respectively. The dating analysis suggests that the divergence time of the two major clades is about 2.74 Mya, which is in the time of the Qinghai-Tibetan plateau uplift. We can suggest that there were two seasons of the two major branch of obvious geographical distribution in yabeana complex. First, the differentiation has occurred among the populations derived from the 3 glacial refugia for the long time geographic isolation during glaciation. Second, the uplift of Qinghai-Tibetan plateau rising the attitude of populations of Clade 1, the difference of attitude caused the isolation of flowering between the populations of Clade 1 and Clade 2, leading to further differentiation.5) The results of phylogenetic analysis suggest that the character of spurless in yabeana complex have occurred repeatedly and independently in the past time. Network analysis of haplotypes suggests that there are shared haplotypes among the type of spurless and other three spur types. These results also suggest that the character of spurless petal is derived from other three types of petals with different status of nectar spurs and originated independently multiple times.