Hai-Qin Sun

Reproductive success of non-rewarding Cypripedium japonicum benefits from low spatial dispersion pattern and asynchronous flowering

BACKGROUND AND AIMS Outcrossing animal-pollinated plants, particularly non-rewarding species, often experience pollinator limitation to reproduction. Pollinator visitation is affected by various factors, and it is hypothesized that reproduction in non-rewarding plants would benefit from low spatial flower abundance and asynchronous flowering. In order to test this hypothesis, the influence of spatial pattern and flowering phenology on male and female reproductive success (RS) was investigated in a non-rewarding orchid, Cypripedium japonicum, in central China over two flowering seasons. METHODS The probabilities of intrafloral self-pollination and geitonogamy caused by pollinator behaviours were estimated from field observations. Pollinator limitation was evaluated by hand-pollination experiments. RS was surveyed in different spatial flower dispersal patterns and local flower densities. The effects of flowering phenological traits on RS were assessed by univariate and multivariate regression analyses. KEY RESULTS Hand-pollination experiments revealed that fruit production was strongly pollen limited throughout the entire reproductive season - over two seasons, 74.3 % of individuals set fruit following hand pollination, but only 5.2-7.7 % did so under natural conditions. Intrafloral self-pollination and geitonogamy within the potential clones might be rare. Both male and female fitness were substantially lower in clustered plants than in those growing singly. An increase in local conspecific flower density significantly and negatively influenced male RS, but had no effect on female RS. Phenotypic selection analysis indicated that individuals flowering earlier have the greatest probability of RS. Over 85 % of sampled flowering individuals had a flowering synchrony value >0.7; however, highly synchronous flowering was not advantageous for RS, as indicated by the negative directional selection differentials and gradients, and by the positive quadratic selection gradients. CONCLUSIONS These results support the hypothesis that, as a consequence of density-dependent selection, low spatio-temporal flower abundance is advantageous for attracting pollinators and for reproduction in natural populations of non-rewarding C. japonicum.

Mountains of Southern China as “Plant Museums” and “Plant Cradles”: Evolutionary and Conservation Insights

Abstract The occurrence of areas or centers of endemism is commonly attributed to the existence of suitable refugia in which plant lineages survived while others evolved during the late Neogene and Quaternary global cooling. In China, several studies performed since the 1980s have identified the mountains of central and southern China as the main centers of endemism in the country. A recent work studied the patterns of endemism separately for palaeoendemics and neoendemics and found that these tend to be located in different mountain ranges. Whereas, young endemics are preferably located in the mountain ranges of the eastern fringe of the Tibetan Plateau (“plant cradles”), old endemics tend to occur in the mountains of central, south central, and southeastern China (“plant museums”), although there are some exceptions. This pattern seems to be related to the different geological history of the mountain ranges. The eastern fringe of the Tibetan Plateau clearly constitutes the “evolutionary front” of China, probably due to the uninterrupted uplift of the plateau from the late Neogene. In contrast, the relative tectonic stability in central and southern China during most of the Tertiary may have maximized the persistence of relict plant lineages. These results have significant implications in the conservation of the endemic flora, which are briefly discussed.

Reproductive isolation and pollination success of rewarding Galearis diantha and non-rewarding Ponerorchis chusua (Orchidaceae)

BACKGROUND AND AIMS Increasing evidence challenges the conventional perception that orchids are the most distinct example of floral diversification due to floral or prezygotic isolation. Regarding the relationship between co-flowering plants, rewarding and non-rewarding orchids in particular, few studies have investigated whether non-rewarding plants affect the pollination success of rewarding plants. Here, floral isolation and mutual effects between the rewarding orchid Galearis diantha and the non-rewarding orchid Ponerorchis chusua were investigated. METHODS Flowering phenological traits were monitored by noting the opening and wilting dates of the chosen individual plants. The pollinator pool and pollinator behaviour were assessed from field observations. Key morphological traits of the flowers and pollinators were measured directly in the field. Pollinator limitation and interspecific compatibility were evaluated by hand-pollination experiments. Fruit set was surveyed in monospecific and heterospecific plots. KEY RESULTS The species had overlapping peak flowering periods. Pollinators of both species displayed a certain degree of constancy in visiting each species, but they also visited other flowers before landing on the focal orchids. A substantial difference in spur size between the species resulted in the deposition of pollen on different regions of the body of the shared pollinator. Hand-pollination experiments revealed that fruit set was strongly pollinator-limited in both species. No significant difference in fruit set was found between monospecific plots and heterospecific plots. CONCLUSIONS A combination of mechanical isolation and incomplete ethological isolation eliminates the possibility of pollen transfer between the species. These results do not support either the facilitation or competition hypothesis regarding the effect of nearby rewarding flowers on non-rewarding plants. The absence of a significant effect of non-rewarding P. chusua on rewarding G. diantha can be ascribed to low levels of overlap between the pollinator pools of two species.

Isolation and characterization of 50 nuclear microsatellite markers for Cathaya argyrophylla, a Chinese endemic conifer

UNLABELLED PREMISE OF THE STUDY Microsatellite primers were developed for the endangered Cathaya argyrophylla (Pinaceae) to investigate its genetic diversity and population genetic structure, as well as its evolutionary history. • METHODS AND RESULTS Fifty dinucleotide microsatellite loci were identified in two populations. The number of alleles per locus ranged from 1 to 6, with a mean of 2.84. The observed and expected heterozygosities ranged from 0 to 0.889 and from 0 to 0.779, respectively. • CONCLUSIONS These markers will facilitate further studies on the population genetics and evolutionary history of Cathaya argyrophylla.

Pollen limitation, reproductive success and flowering frequency in single‐flowered plants

Flowering plants exhibit striking interspecific and intraspecific variation in flower number, which strongly influences the reproductive success of animal-pollinated plants. However, the reproductive consequences of producing a single flower are poorly understood. Here, we test if plants producing a single flower have a reproductive disadvantage compared with plants producing multiple flowers by combining field investigation of five deceptive orchids and a survey of published literature. Pollen limitation was estimated by comparing fruit production between hand pollination and open pollination. Flowering frequency was monitored over years to assess the potential advantage of producing a single flower. Both single- and multiple-flowered species suffered strong pollen limitation. However, single-flowered species had significantly lower fruit set and produced fewer seeds per individual, although they had a significantly higher pollen removal than species with multiple flowers. A phylogenetically independent contrast of 28 species representing four of the five subfamilies of Orchidaceae revealed that fruit set was significantly positively associated with flower number. Both pollen removal and fruit set had a positive relationship with flower number within the multiple-flowered species. Synthesis. Current data and phylogenetically independent contrast support the hypothesis that producing a single flower has reproductive disadvantages. Single-flowered species may compensate for low female success through high flowering frequency over years. This study provides insight into costs and benefits of producing a single flower in deceptive orchids.