Spatial distribution and sexual dimorphism of dioecious Arisaema erubescens

doi:10.17520/biods.2024084

Abstract

Abstract:

Aims: The transition to dioecy constitutes a pivotal milestone in the evolution of sexual functions in flowering plants, marking a shift from the integration of male and female reproductive organs within the same individual to their separation. This sexual system occurs across numerous angiosperm families and genera. Both female and male individuals of dioecious species display variations in distribution, morphology, and life history traits. Therefore, it is essential to examine the spatial distribution and sexual dimorphism of dioecious species in order to comprehend their reproductive strategies, adaptability, and evolutionary patterns. The genus Arisaema is the only reported taxon within the Araceae family known to possess a dioecious sexual system. In this study, we explored the differences between the dioecious members of Arisaema erubescens in the Badagongshan National Nature Reserve, Hunan Province, China, with a specific focus on the spatial distribution and sexual dimorphisms.
Methods: We surveyed the coordinate positions of male and female individuals across four plots, analyzed both the sex ratio and spatial distribution patterns of these individuals. Sexual dimorphism was assessed based on phenological and morphological traits of A. erubescens. Additionally, a quantitative comparison of the floral visitor assemblages between female and male individuals was conducted.
Results: From our observations, the A. erubescens population was significantly dominated by staminate flora. Male and female individuals were found to clusters on small scales and disperse randomly on a large scale. The male individuals flowered 4 days earlier than the females. The permutational multivariate analysis of variance identified significant disparities in morphological traits between male and female individuals, which are pivotal to sexual dimorphism. These traits include the pseudostem basal diameter, the diameter of spathe tube, the inflorescence basal diameter, and the peduncle diameter. The primary pollinators of A. erubescens were the diurnal fungus gnats of the Mycetophila species, with an extremely higher visitation frequency observed on male individuals compared to those on female individuals.
Conclusions: Our study suggests that the spatial association of different genders in A. erubescens corresponds to the pollinators’ activity habits. The sex dimorphism of A. erubescens in flowering phenology, morphological traits, and pollination activity collectively guaranteed the reproductive success of the species.

Key words: Arisaema erubescens, dioecy, sex dimorphism, sex ratio, spatial distribution, sexual reproduction traits, pollination by fungus gnats

Weijie Shu, Hua He, Luo Zeng, Zhirong Gu, Dunyan Tan, Xiaochen Yang. Spatial distribution and sexual dimorphism of dioecious Arisaema erubescens[J]. Biodiv Sci, 2024, 32(6): 24084.

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URL: https://www.biodiversity-science.net/EN/10.17520/biods.2024084

https://www.biodiversity-science.net/EN/Y2024/V32/I6/24084

Figures/Tables 8

Fig. 1 Schematic of individual and floral morphology of Arisaema erubescens. (A) Individual; (B) External morphology of spathe; (C) Female spathe vertical-section; (D) Male spathe vertical-section. 1, Inflorescence height; 2, Pseudostem length; 3, Pseudostem basal diameter; 4, Peduncle length; 5, Peduncle diameter; 6, Spathe length; 7, Limb width of spathe; 8, Tube length of spathe; 9, Tube diameter; 10, Throat diameter; 11, Inflorescence length; 12, Inflorescence basal diameter; 13, Inflorescence apical diameter; 14, Appendix length; 15, Appendix diameter; 16, Exit hole at the base of spathe in male individual; 17, Channel diameter.

Table 1 Sex ratio of Arisaema erubescens in four samples in the Badagongshan National Nature Reserve in 2022. P < 0.01 indicates an extremely significant deviation from a 1 : 1 sex ratio.

样方 Sample	雄株 Male	雌株 Female	性比(雄 : 雌) Sex ratio (Male : Female)	G-检验 G-test	P
1	38	15	2.53	10.321	0.001
2	34	11	3.09	12.330	< 0.001
3	41	12	3.42	16.773	< 0.001
4	36	12	3.00	12.558	< 0.001

Fig. 2 Spatial distribution of Arisaema erubescens in four samples in the Badagongshan National Nature Reserve in 2022

Fig. 3 Spatial associations between male and female individuals of Arisaema erubescens in four samples in the Badagongshan National Nature Reserve. The dark lines and light lines are g(r) values and 99% confidence envelopes, respectively.

Fig. 4 Flowering phenology of Arisaema erubescens in the Badagongshan National Nature Reserve in 2022 (A) and 2023 (B)

Table 2 Comparisons of traits between male and female individuals of Arisaema erubescens (generalized linear model, GLM) (mean ± SE). The larger value of significant differences (P < 0.05) is indicated in bold.

特征 Traits	雌株 Female individual	雄株 Male individual	Wald χ²	P
叶数 Leaf number	1.29 ± 0.08	1.00 ± 0.00	14.543	< 0.001
花序高度 Inflorescence height (cm)	57.40 ± 1.42	44.26 ± 1.35	44.899	< 0.001
假茎长 Pseudostem length (cm)	39.78 ± 2.05	26.65 ± 1.18	30.352	< 0.001
假茎基径 Pseudostem basal diameter (mm)	12.39 ± 0.44	7.85 ± 0.43	54.421	< 0.001
花序柄长 Peduncle length (cm)	9.76 ± 0.73	11.51 ± 0.57	3.530	0.06
花序柄直径 Peduncle diameter (mm)	4.91 ± 0.21	3.14 ± 0.15	48.564	< 0.001
佛焰苞长 Spathe length (mm)	76.26 ± 1.60	65.69 ± 2.60	12.219	< 0.001
佛焰苞檐宽 Limb width of spathe (mm)	45.96 ± 1.28	39.24 ± 1.19	1.044	0.307
佛焰苞管长Tube length of spathe (mm)	48.04 ± 1.69	42.14 ± 1.72	5.969	0.015
管部直径 Tube diameter (mm)	12.92 ± 0.26	8.89 ± 0.28	112.205	< 0.001
喉部直径 Throat diameter (mm)	15.46 ± 0.67	12.31 ± 0.50	14.079	< 0.001
花序长 Inflorescence length (mm)	21.71 ± 0.60	25.79 ± 0.85	15.551	< 0.001
花序基径 Inflorescence basal diameter (mm)	10.07 ± 0.29	5.35 ± 0.21	175.015	< 0.001
花序顶径 Inflorescence apical diameter (mm)	6.02 ± 0.15	3.70 ± 0.13	135.609	< 0.001
小花数 Number of floret	515.79 ± 22.48	263.04 ± 12.24	95.747	< 0.001
附属器长 Appendix length (mm)	38.76 ± 1.92	27.20 ± 1.62	21.014	< 0.001
附属器直径 Appendix diameter (mm)	4.95 ± 0.26	4.71 ± 0.26	0.430	0.512
小花直径 Floret diameter (mm)	1.17 ± 0.02	1.34 ± 0.03	32.098	< 0.001
出口孔截面积 Exit hole cross-sectional area (mm)	-	4.26 ± 0.36	-	-
通道直径 Channel diameter (mm)	-	2.00 ± 0.09	-	-

Fig. 5 Principal component (PC) analysis of traits in two sex phenotypes of Arisaema erubescens in the Badagongshan National Nature Reserve

Fig. 6 Visit frequency by different visitors between male and female inflorescences (A) and temporal dynamics of the visitors number (B) of Arisaema erubescens (mean ± SE). ** indicates significant difference of visit frequency between male and female individuals at P < 0.01, while ns indicates no significant difference. Different capital and lowercase letters in (B) indicate significantly different visitor number in male and female inflorescences between different time of the day at P < 0.05, respectively.

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