Floral syndrome and secondary pollen presentation in Codonopsis clematidea(Campanulaceae)

doi:10.3724/SP.J.1003.2011.10167

Abstract

Abstract:

Secondary pollen presentation has been described as a reproductive strategy that enhances the efficiency and accuracy of pollen exportation and pollen reception, thereby promoting outcrossing. Codonopsis clematidea is characterized by secondary pollen presentation. The objective of this research is to study the floral syndrome and the procedure of secondary pollen presentation of this species, with special reference to the adaptive significance of these features based on the field observations, hand-pollination experiments and indoor microscopic observations. The results showed that the blue campanulate pendulous corolla and black and yellow nectary of C. clematidea not only protect the androecium and gynoecium from rain damage and prevent rain water from diluting the nectar and removal of pollen by wind, but they also attract more pollinators and extend the duration of pollen viability and stigma receptivity. The secondary pollen presentation of this species is sub-terminal stylar presenters and belongs to the deposition mechanism. This character limits the amount of pollen removed by the pollinators and prolongs pollen presentation, thus attracting more pollinators and thereby increasing male fitness. The protandry and the change of the spatial position of male and female organs during the flowering stage of C. clematidea not only avoid interference between male and female functions, but also create a passageway for pollinators to forage for nectar and pollen and for stigmas to receive outcross pollen. Bombus silvarum, B. paradoxusandDolichovespula sylvestris are the effective pollinators in the generalist pollination system of this species. Other floral characteristics of this species, such as long flowering duration (approximately 6 d) per flower, overlap of the peak of insects visitation in the male and female phases with the period of highest pollen viability and the optimal stigma receptivity of pollen, lots of nectar that contains a higher sugar concentration and a long period of nectar secretion during the flowering stage, etc, enhance visitation frequencies and the chances of successful pollination. Therefore, these traits help improve pollination efficiency and promote outcrossing. The special floral syndrome and the mechanism of secondary pollen presentation are significant in improving pollination efficiency and promoting the reproductive success of Codonopsis clematidea by outcrossing under changeable weather conditions in Tianshan Mountains.

Key words: Codonopsis clematidea, floral syndrome, outcrossing, prodandry, secondary pollen presentation

Li Wang, Dunyan Tan. Floral syndrome and secondary pollen presentation in Codonopsis clematidea(Campanulaceae)[J]. Biodiv Sci, 2011, 19(1): 24-33.

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URL: https://www.biodiversity-science.net/EN/10.3724/SP.J.1003.2011.10167

https://www.biodiversity-science.net/EN/Y2011/V19/I1/24

Figures/Tables 7

Fig. 1 Codonopsis clematidea flowering stages. (A) Anthers are closed around the style within the unopened bud; (B) Anthers disperse pollen onto the back of stigma lobes; (C) Pollens are deposited onto the stylar hairs via anthers and style separation; (D) End of pollen release; (E) Stigma lobes spreading; (F) Withered stigma and corolla showing end of anthesis. An, Anther; Es, External surface of still unexpanded stigma; Fi, Filament; Ne, Nectary; Po, Pollen; Sti, Stigma; Sty, Style. Scale bar = 1 mm.

Fig. 2 The course of successive stylar hairs invaginated in Codonopsis clematidea. (A) Unicellular hairs of the style within the unopened bud; (B) Pollens between hairs are exposed and released by successive invagination of hairs; (C) Dotted with pits formed by withdrawal of stylar hairs. Dw, Dotted with pits; Hi, Hair invaginating; Sh, Stylar hairs; Po, Pollen. Scale bar = 0.5 mm.

Fig. 3 Pollen viability in Codonopsis clematidea(Mean±SE,n = 10). A, Beginning of dehiscence of anthers; B, End of dehiscence and beginning of pollen release; C-E, Pollen is released for 24 h (C), 48 h (D), and 72 h (E).

Fig. 4 The pollinators ofCodonopsis clematidea. A-C, Flowers in male phase; D-F, Flowers in female phase. A and D,Bombus silvarum; B and E,Dolichovespula sylvestris; C and F,B. paradoxus. Scale bar = 1 mm.

Fig. 5 Visiting frequency of pollinators (Mean±SE,n = 30)

Fig. 6 Nectar volume and sugar content in Codonopsis clematidea flowers (Mean±SE,n = 30)

Table 1 Effect of different pollination treatments on fruit set and seed set in Codonopsis clematidea(Mean ± SE)

授粉处理 Pollination treatment	n	座果率 Fruit-set (%)	结籽率 Seed-set (%)
(1) 不去雄套袋 Bagged without emasculation	30	0^a	0^a
(2) 去雄套网袋 Emasculated and bagged with nylon net	30	0^a	0^a
(3) 人工自花授粉 Artificial autogamy	30	0^a	0^a
(4) 人工异株异花授粉 Artificial xenogamy	30	73.3^b	83.7 ± 4.4 ^b
(5) 自然授粉 Natural pollination	30	66.7^b	80.6 ± 2.4 ^b

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