Journal Article

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

Hai-Qin Sun, Jin Cheng, Fu-Min Zhang, Yi-Bo Luo and Song Ge

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 103, issue 8, pages 1227-1237
Published in print June 2009 | ISSN: 0305-7364
Published online March 2009 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcp066
Reproductive success of non-rewarding Cypripedium japonicum benefits from low spatial dispersion pattern and asynchronous flowering

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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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.

Keywords: Cypripedium japonicum; pollen limitation; spatial dispersal pattern; flowering synchrony; reproductive success; selection differential; selection gradient; deceptive flower

Journal Article.  8185 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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