Floral biology, breeding systems and population genetic structure of three climbingBauhiniaspecies (Leguminosae: Caesalpinioideae) in Hong Kong, China

Abstract

Abstract:The pollination ecology, breeding system and population genetic structure of three climbingBauhiniaspeciesB. championii(4 populations, 23 individuals),B. corymbosa(2 populations, 25 individuals) andB. glauca(8 populations, 76 individuals) were studied in Hong Kong, southern China. We hypothesize that the climbingBauhiniaspecies will attract targeted pollinators to achieve out-cross success and high levels of self-incompatibility will be expected to maintain diversity, with local population expansion relying on vegetative propagation. All three species have inflorescences consisting of numerous small, pale, fragrant flowers, which show diurnal anthesis. Field observations revealed that all three species are predominantly pollinated by bees (particularlyApis mellifera) and butterflies (GraphiumandPapiliospecies), althoughB. championiiis also pollinated by wasps and flies.Bauhinia corymbosaandB. glaucahave sucrose-dominant nectar, whereasB. championiihas hexose-dominant nectar. In controlled-pollination experiments fruit and seed set were generally highest following artificial out-crossing. The index of self-incompatibility ofB. championiiis 1.07, indicating self-compatibility;B. corymbosaandB. glaucawere obligately self-incompatible. The population genetic structure and variation of theBauhiniaspecies was investigated using ISSR markers. Generally the three species have moderate within-population (meanHS= 0.206) and high among-population genetic variation (meanGST= 0.284). No correlation exists between the geographical and genetic distance, possibly due to the small local population size. All three species showed high levels of heterozygosity as expected for predominantly out-crossing long-lived K-selected species.