Adaptive significance of mass-flowering in Hedychium coccineum (Zingiberaceae)

doi:10.3724/SP.J.1003.2012.10034

Abstract

Abstract:

Hermaphroditic plants that simultaneously display multiple flowers may attract more pollinators and create more chances for mating. However, this may also lead to geitonogamy, which may have major impacts on evolution of sex allocation, floral characteristics, and dioecy. To explore adaptive significance of mass-flowering in Hedychium coccineum, we conducted studies on pollination biology of H. coccineum, via hand-pollination and manipulated experiments, pollinator observation, and investigations on population density and natural fruit sets. Overall, inflorescences of H. coccineum were composed of terminal spikes containing 57.33 ± 1.68 (n = 30) cincinnus, and each cincinnus possessed 3.8 ± 0.15 (n = 30) flowers. Flowers in each cincinnus opened in turn, and the same round flowers among each cincinnus within inflorescences opened in successive synchronous cycles. This provided a spike that kept a mass of flowers blooming simultaneously throughout the flowering period. H. coccineum displayed a large floral display at the inflorescence level. Additionally, H. coccineum was self-compatible, and spontaneous self-pollination did not occur. Fruit production of H. coccineum in natural populations was severely pollinator-limited. Meanwhile, H. coccineum was also resource-limited in fruit production. Three butterflies, Papilio memnon, Dercas lycorias, and Appias indra aristoxemus were effective pollinators of H. coccineum. Visiting frequencies of these butterfly species to three inflorescences with different floral display size were obviously different and visitation frequencies increased as the inflorescence increased in floral display size. Pollen grains and ovules of H. coccineum varied significantly among flowers of different rounds in the cincinnus. Ovule production decreased significantly from the first to the fourth round, but pollen grains increased significantly from the first round to the third round. The decrease in ovules and resource limitation in fruit production indicated that mass-flowering in H. coccineum was not for increasing fruit production. The increase in pollen grains from the first round to the third round benefits pollen export and increases male fitness.

Key words: Hedychium, floral display, floral longevity, flowering pattern, geitonogamy, inflorescence structure, sex allocation

Jiangyun Gao, Chunling Sheng, Shuxia Yang. Adaptive significance of mass-flowering in Hedychium coccineum (Zingiberaceae)[J]. Biodiv Sci, 2012, 20(3): 376-385.

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URL: https://www.biodiversity-science.net/EN/10.3724/SP.J.1003.2012.10034

https://www.biodiversity-science.net/EN/Y2012/V20/I3/376

Figures/Tables 6

Fig. 1 Inflorescence and visitors of Hedychium coccineum. (a) An inflorescence of Hedychium coccineum contains many cincinnus, and flowers in a cincinnus blooms on turn, and many flowers bloom on an inflorescence at the same time. (b) A Papilio memnon is visiting the inflorescence of H. coccineum. (c) A Dercas lycorias is visiting the inflorescence of H. coccineum. (d) A number of pollen grains of H. coccineum are stuck on the wing of a visiting Dercas lycorias. The arrow indicates the pollen grains.

Table 1 Plant and floral characteristics of Hedychium coccineum

项目 Items	平均值±标准差 Mean ± SE	范围 Range	样本量 Simple size
株高 Plant height (m)	1.72 ± 0.05	1.2-2.3	30
小花序数 No. of cincinnus per inflorescence	57.33 ± 1.68	38-75	30
花数 No. of flowers per cincinnus	3.8 ± 0.15	2-6	30
花丝长度 Filament length (mm)	55.7 ± 0.66	49.82-62.11	30
花药长度 Anther length (mm)	10.08 ± 0.2	8-12.12	30
花柱长度 Style length (mm)	99.86 ± 0.90	88.72-105.27	30
花冠管长度 Corolla tube length (mm)	34.05 ± 0.48	29.61-39.82	30
唇瓣长度 Labellum length (mm)	27.55 ± 0.23	24.64-29.68	30
唇瓣宽度 Labellum width (mm)	17.55 ± 0.29	13.32-20.84	30
花粉数 No. of pollen grains	6,960.8 ± 168.2	3,600-11,775	90
胚珠数 No. of ovules	75.47 ± 1.59	45-118	90

Fig. 2 The pollen grains and ovule number of different round flowers in cincinnus of Hedychium coccineum. Statistically homogeneous grouping based on ANOVA analysis are indicated by the same letter (A, B or C for pollen grains and a, b, c or d for ovule number(P < 0.001).

Fig. 3 The effects of pollination treatments on fruit set of Hedychium coccineum in 2005 and 2006. Statistically homogeneous grouping based on a one-way analysis of variance are indicated by the same letter (A or B for 2005 and a, b or c for 2006) above the bars(P < 0.001).

Fig. 4 The growth pattern of pollen tube in the style of Hedychium coccineum under two pollination treatments

Fig. 5 The visitation patterns on the 3 different inflorescences of Hedychium coccineum by Papilio memnon, Dercas lycorias and Appias indra aristoxemus (26-29 July 2007)

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