Development and characterization of microsatellite loci for the endemic Thalictrum smithii (Ranunculaceae).

PREMISE OF THE STUDY: Microsatellite primers were developed for the gynodioecious Chinese endemic Thalictrum smithii (Ranunculaceae). METHODS AND RESULTS: Thirty-nine microsatellite primers were developed using the Fast Isolation by AFLP of Sequences COntaining repeats (FIASCO) method. Thirteen microsatellite loci were found to be highly polymorphic after screening 114 specimens (60 hermaphrodite and 54 female) from three T. smithii populations. The number of alleles per locus ranged from three to 13, and the levels of observed and expected heterozygosity per locus ranged from 0.000 to 1.000 and from 0.204 to 0.834, respectively. Twenty-six of these primers were polymorphic in T. petaloideum and T. finetii. CONCLUSIONS: These markers will be useful for examining genetic diversity, polyploidy, and mating system in populations of T. smithii and for guiding study on the evolution of speciation in Thalictrum.

Generalist passerine pollination of a winter-flowering fruit tree in central China.

BACKGROUND AND AIMS: Winter-flowering plants outside the tropics may experience a shortage of pollinator service, given that insect activity is largely limited by low temperature. Birds can be alternative pollinators for these plants, but experimental evidence for the pollination role of birds in winter-flowering plants is scarce. METHODS: Pollinator visitation to the loquat, Eriobotrya japonica (Rosaceae), was observed across the flowering season from November to January for two years in central China. Self- and cross-hand pollination was conducted in the field to investigate self-compatibility and pollen limitation. In addition, inflorescences were covered by bird cages and nylon mesh nets to exclude birds and all animal pollinators, respectively, to investigate the pollination role of birds in seed production. RESULTS: Self-fertilization in the loquat yielded few seeds. In early winter insect visit frequency was relatively higher, while in late winter insect pollinators were absent and two passerine birds (Pycnonotus sinensis and Zosterops japonicus) became the major floral visitors. However, seed-set of open-pollinated flowers did not differ between early and late winter. Exclusion of bird visitation greatly reduced seed-set, indicating that passerine birds were important pollinators for the loquat in late winter. The whitish perigynous flowers reward passerines with relatively large volumes of dilute nectar. Our observation on the loquat and other Rosaceae species suggested that perigyny might be related to bird pollination but the association needs further study. CONCLUSIONS: These findings suggest that floral traits and phenology would be favoured to attract bird pollinators in cold weather, in which insect activity is limited.

Parthenogenesis maintains male sterility in a gynodioecious orchid.

The invasion of male-sterile (female) individuals into hermaphroditic populations, leading to gynodioecy, is common in flowering plants. Both theoretical and empirical studies have shown that as the frequency of females increases in a population, pollen limitation reduces seed production more in females than in hermaphrodites, leading to higher fitness for hermaphrodites and a consequent decrease in female frequency. Here we show that contrary to this expectation, females of the gynodioecious orchid Satyrium ciliatum are maintained only in populations that experience high pollen limitation caused by low pollinator service and high pollen herbivory. This species avoids the typical problem of pollen limitation for seed production and can therefore maintain high frequencies of females in pollen-limited populations because females produce more seeds than hermaphrodites via facultative parthenogenesis in the absence of pollinia. Our results therefore demonstrate that parthenogenesis is a novel mechanism favoring the maintenance of gynodioecy.