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

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)"

Corolla length
Corolla width
Corolla height
Tube length
Entrance height
Tube entrance height
Tube entrance width
Filament length
Pistil length
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
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)"

No. of infloresce-
nce in individual
No. of branch
in a false panicle
No. of verticillaster
in a false raceme
No. of flower in
a verticillaster
No. of flowering
in a verticillaster
Total no. of
flower in
individual plant
Total no. of
flowering in
individual plant
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)
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)"

Relative frequency
Visit time per flower (s)
Activity rate
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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