Biodiversity Science ›› 2017, Vol. 25 ›› Issue (6): 608-614.doi: 10.17520/biods.2017039

• Original Papers • Previous Article     Next Article

Reproductive isolation in sympatric Salvia species sharing a sole pollinator

Yukun Wei*(), Yanbo Huang, Guibin Li   

  1. Shanghai Chenshan Plant Science Research Center, Chinese Academy of Sciences; Shanghai Chenshan Botanical Garden, Shanghai 201602
  • Received:2017-05-27 Accepted:2017-06-21 Online:2017-07-10
  • Wei Yukun E-mail:ykwei@sibs.ac.cn

Reproductive isolation (RI) is one of the key factors for speciation and diversity maintenance, however, there are differences in formation stage, means, and strength of RI for different species. To assess the effects and the significance of reproductive isolation in Salvia species, we compared flowering, pollination, and reproduction characteristics of Salvia liguliloba and S. bowleyana, which grow sympatrically and have overlapping flowering periods in the Tianmu Mountain, Zhejiang. Furthermore, artificial hybridization between the two species were conducted to estimate and understand their genetic compatibility and reproductive isolation. Results indicated that the two Salvia species considerably differed in their flower morphological structures, inflorescence organization, and the number of flowers produced per inflorescence. Bombus trifasciatus is the sole pollinator for these two species during the overlapping flowering period. However, different visitation behavior and floral structure (P < 0.05) leads to obviously different pollination patterns between the two species. Pollen is deposited on distinctly separate areas of the pollinator’s body in a manner precluding contact with any heterospecific Salvia stigmata. Under natural condition, the two species are equally successful in reproduction (natural seed set > 87%). Artificial pollination and hybridization experiments between these two species showed that they have a higher genetic compatibility. The cross seed sets are 77.8 ± 10.7% and 78.7 ± 11.2% when the two species are reciprocally cross parents. Our research suggests that for the two Salvia species lacking genetic incompatibility systems and relying on pollinators for outcrossing, there are differences in floral structures and pollen placement sites. The mechanical isolation (a form of pre-pollination RI) prevents heterospecific pollen interference and natural hybridization of the two different species that grow sympatrically and have overlapping flowering periods, and also maintains species diversity and the constancy of species heredity.

Key words: mechanical isolation, genetic compatibility, species diversity, natural hybridization, Bombus trifasciatus

Fig. 1

Comparison of inflorescences, flower structures, and insect pollinations of Salvia liguliloba and S. bowleyana (Bar = 2 mm). (a) Inflorescences of S. liguliloba; (b) Flower lateral dissection of S. liguliloba (the arrow indicates anther); (c) A front view of S. liguliloba flower; (d) Bombus trifasciatus is visiting flowers and pollinating S. liguliloba (the arrow indicates pollen placement sites on bumblebee); (e) Inflorescences of S. bowleyana; (f) Flower lateral dissection of S. bowleyana (the arrow indicates anther); (g) A front view of S. bowleyana flower; (h) Bombus trifasciatus is visiting flowers and pollinating S. bowleyana (the arrow indicates pollen placement sites on bumblebee)."

Table 1

Comparison of flower structures between Salvia liguliloba and S. bowleyana (mean ± SD)"

花冠长
Corolla length
花冠宽
Corolla width
花冠高
Corolla height
冠筒长
Tube length
冠口高
Entrance height
冠筒口高
Tube entrance height
冠筒口宽
Tube entrance width
花丝长
Filament length
药隔长
Connective
length
雌蕊长
Pistil length
舌瓣鼠尾草
S. liguliloba
23.7 ± 0.74a 5.31 ± 0.34a 7.30 ± 0.67b 19.5 ± 0.8a 4.87 ± 0.61b 4.87 ± 0.61a 4.41 ± 0.52a 2.39 ± 0.14b 5.19 ± 0.33b 23.7 ± 0.43b
南丹参
S. bowleyana
22.8 ± 1.10b 4.47 ± 0.26b 16.6 ± 0.94a 12.4 ± 0.76b 11.2 ± 0.80a 4.47 ± 0.28a 3.21 ± 0.23b 4.30 ± 0.26a 14.3 ± 0.68a 26.1 ± 1.85a
P 0.0407 0.000 0.000 0.000 0.000 0.0585 0.000 0.000 0.000 0.0011

Table 2

Comparisons of flowering and inflorescence between Salvia liguliloba and S. bowleyana (mean ± SD)"

单株花序总数
No. of infloresce-
nce in individual
plant
假圆锥花序
分枝数
No. of branch
in a false panicle
假总状花序的
轮伞花序数
No. of verticillaster
in a false raceme
轮伞花序小
花总数
No. of flower in
a verticillaster
轮伞花序同时
开放小花数
No. of flowering
in a verticillaster
单株总花数
Total no. of
flower in
individual plant
单株总开花数
Total no. of
flowering in
individual plant
舌瓣鼠尾草
S. liguliloba
2.0±2.1a (n = 35) 2.0±1.9b (n = 39) 9.3±2.4a (n = 83) 5.6±1.1b (n = 93) 1.4±1.7b (n = 234) 262±299b (n = 26) 21±30a (n = 36)
南丹参
S. bowleyana
2.2±0.45a (n = 5) 5.8±3.0a (n = 11) 9.5±1.9a (n = 40) 9.8±1.9a (n = 160) 1.8±1.0a (n = 160) 891±472a (n = 5) 48±56a (n = 16)
P 0.681 0.0020 0.7166 0.000 0.0053 0.0005 0.089

Table 3

Comparisons of flower visiting behavior of Bombus trifasciatus between Salvia liguliloba and S. bowleyana (mean ± SD)"

相对频次
Relative frequency
单花访问时间
Visit time per flower (s)
活跃度
Activity rate
访花频率
Visitation rate
舌瓣鼠尾草 S. liguliloba 0.14 ± 0.017 b (n = 3) 2.01 ± 0.85 a (n = 30) 9.71 ± 3.15 b (n = 7) 1.36 ± 0.17 b (n = 3)
南丹参 S. bowleyana 0.86 ± 0.017 a (n = 3) 1.80 ± 0.63 a (n = 30) 16.2 ± 3.4 a (n = 52) 13.9 ± 0.28 a (n = 3)
P 0.000 0.2758 0.000 0.000

Fig. 2

Comparisons of cross-pollination, self-pollination, and hybridization of Salvia liguliloba and S. bowleyana. (A) and (B) show S. liguliloba and S. bowleyana, respectively. Different letters indicate significant difference at the level of P < 0.05 by t-test."

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