普遍认为, 被子植物中虫媒传粉植物丰富的多样性是其花性状响应传粉环境(传粉者)的空间变异而发生适应性趋化的结果(Herrera et al., 2006), 即传粉者塑造了花特征的多样性进化(Stebbins, 1974; Huang & Guo, 2000; 王林林等, 2011)。当居群间基因交流受限、传粉者具有空间上的异质性, 即各居群的传粉者在组成和多度上存在变异时会导致传粉系统的地理趋异(Stebbins, 1970; Thompson, 1994; Campbell, 2008; Harder & Johnson, 2009), 相应地将引起花性状的局域适应分化(local adaptive diversification)。
鼠尾草属(Salvia)是唇形科最大的一个属, 广泛分布于世界各地(Walker & Sytsma, 2007)。该属植物最显著的特点是大部分物种具有高度特化的杠杆状雄蕊(lever-like stamens)及背部传粉(dorsal pollination)机制(Claßen-Bockhoff et al., 2003)。Sprengel (1793)首次描述了鼠尾草属植物通过雄蕊杠杆运动进行的背部传粉机制。19世纪中后期, 研究者通过形态学和解剖学研究揭示了杠杆状雄蕊的结构多样性及形态发生过程(Claßen-Bockhoff et al., 2004a)。近年来, 关于鼠尾草属杠杆状雄蕊的研究主要集中在传粉生态(Barrett et al., 2000; Ohashi, 2002; Claßen-Bockhoff et al., 2004b; Wester & Claßen-Bockhoff, 2006; Zhang et al., 2011)和系统进化方面(Walker & Sytsma, 2007)。传粉生态学证据表明, 雄蕊杠杆机制与传粉者的访花忠实性密切相关(Zhang et al., 2011), 可通过促进异交、精确传粉和花粉分发等途径影响植物的繁殖成功(Claßen- Bockhoff et al., 2004b; Reith et al., 2007; 张勃等, 2010)。鉴于雄蕊杠杆结构的多样性及其在传粉系统中发挥的重要作用, Claßen-Bockhoff等(2004b)提出了“杠杆状雄蕊可能作为关键性状(a key innovation)激发了该属物种的适应性辐射”的假说。Walker和Sytsma (2007)通过分子系统学研究表明, 杠杆状雄蕊在鼠尾草属中发生了多次独立进化, 并在不同进化分支内均伴随有雄蕊杠杆结构的多样化和物种的适应辐射。然而, 目前对于该属物种适应辐射的生态学过程知之甚少, 有关雄蕊杠杆机制的地理趋异和适应性的研究尚未见报道。
本文对鼠尾草属3个物种(共4个居群)的花性状和传粉系统进行了比较研究, 探讨了杠杆状雄蕊及相关花部性状对传粉环境空间变异的进化响应, 为揭示该属物种的多样性分化及适应机制提供了一定的证据支持, 希望对进一步探索该属物种的适应辐射过程有所启示。
1 材料和方法
1.1 试验材料和地点
本研究选取了不同地理分布的鼠尾草属3个物种共4个居群, 见表1。毛地黄鼠尾草(S. digitaloides) 2个居群: 低海拔(2660 m)的早花居群和高海拔(3200 m)的晚花居群; 早花居群的花期为4-5月, 晚花居群为8-9月, 两居群的花均为乳白(或乳黄)色, 花冠口有红色或紫红色斑点。圆苞鼠尾草(S. cyclostegia)居群位于海拔3160 m, 花期为5-6月 初, 花白色, 花冠口少有紫色斑点。近掌脉鼠尾草(S. subpalmatinervis)居群位于海拔3350 m, 花为紫红色, 花冠口多有白色斑点, 花期为7-8月。
表1 鼠尾草不同物种居群的概况和花部性状比较(平均值±标准误差)
Table 1
| 物种/居群 Species/Population | 毛地黄鼠尾草I S. digitaloides I | 毛地黄鼠尾草II S. digitaloides II | 近掌脉鼠尾草 S. subpalmatinervis | 圆苞鼠尾草 S. cyclostegia | |
|---|---|---|---|---|---|
| 居群描述 Population description | |||||
| 地点 Location | 丽江干河坝 Ganheba in Lijiang | 丽江甘海子 Ganhaizi in Lijiang | 中甸纳帕海 Napahai in Zhongdian | 丽江文海 Wenhai in Lijiang | |
| 经纬度 Longitude/Latitude | 27°04.307′ N 100°14.683′ E | 27°00.897′ N 100°14.671′ E | 27°55.377′ N 99°38.060′ E | 27°00.447′ N 100°09.334′ E | |
| 海拔 Altitude (m) | 3 200 ± 10 | 2 660 ± 10 | 3 350 ± 10 | 3 160 ± 25 | |
| 花期 Flowering period | 7-9月 July-Sept. | 4-5月 Apr.-May | 7-8月 July-Aug. | 5月 May | |
| 花部性状 Floral trait (mm) | n = 86 | n = 33 | n = 53 | n = 36 | |
| 冠长 Corolla length | 32.14 ± 0.23a | 30.81 ± 0.30ab | 31.58 ± 0.42ab | 30.19 ± 0.37b | |
| 雄蕊杠杆长 Stamen lever length | 4.55 ± 0.05c | 5.25 ± 0.07b | 4.66 ± 0.08c | 5.83 ± 0.06a | |
| 冠口高 Corolla entrance height | 5.30 ± 0.05c | 6.02 ± 0.10b | 5.37 ± 0.07c | 6.48 ± 0.10a | |
| 柱高 Stigma height | 5.53 ± 0.12b | 6.70 ± 0.17a | 4.36 ± 0.13c | 6.99 ± 0.21a | |
| 柱头探出距离 Style exertion | 3.95 ± 0.10b | 4.41 ± 0.17ab | 4.81 ± 0.13a | 4.47 ± 0.24ab | |
不同小写字母表示差异显著(p < 0.05)。
Different small letters represent significant difference (p < 0.05).
1.2 花部性状测量
在盛花期, 根据居群大小随机选择40-100个单株, 用电子游标卡尺测量各物种花部结构性状的大小。测量性状包括花冠长、柱头探出距离、柱头高度(柱头和花冠口下沿的距离)、雄蕊杠杆长度、冠口高度和宽度, 共5个花部性状(如图1所示)。每个单株测量4-5朵花, 其平均值作为单株花性状表型值, 所有单株表型值的平均作为居群花性状的表型值。
图1
图1
鼠尾草花部性状测量示意图。A, 花的侧面图。B, 雄蕊杠杆放大图。C, 花的正面图。ceh, 冠口高; cew, 冠口宽; cl, 花冠长; se, 柱头探出距离; sll, 雄蕊杠杆长度; sth, 柱头高度。
Fig. 1
Morphometrics of flower in Salvia. A, side view of a flower. B, enlarged view of stamen lever. C, front view of a flower. ceh, corolla entrance height; cew, corolla entrance width; cl, corolla length; se, style exsertion; sll, stamen lever length; sth, stigma height.
1.3 访花观察和传粉者体型测量
根据居群密度和开花情况选择1 m × 1 m或1 m × 2 m的样方, 选择晴天在各居群传粉者访花高峰期(10:00-15:00), 观察和记录各类传粉者的访花频次; 各居群每次(天)持续观察2 h, 共观察3-4次(天)。访花期间, 用秒表测量不同类型传粉者的单花访花时间(s), 即访花者从登陆花冠口下唇到访花结束后飞离花冠的整个时间; 同时用相机拍摄其访花姿态。访花观察快结束时, 对居群中出现的不同类型的传粉者, 各采集标本4-6只, 用电子游标卡尺现场测量其体长、胸厚和喙长(测量时用大头针先将活体蜂固定, 待其自然伸展时进行测量; 测量喙长时, 用镊子将其拉出至自然伸展长度), 然后带回实验室进行鉴定。
1.4 传粉者的访花率指数
访花率指数(visitation rate index, IVR)同时考虑了传粉者在居群所有传粉者中所占的相对频率及其访花效率, 用以评估不同类型的传粉者在居群所有传粉者中的相对重要性(Talavera et al., 2001)。
IVR = F × AR
F是某类传粉者在居群中出现的相对频次; AR是传粉者的访花效率(the activity rate), 用传粉者每分钟的访花数表示, 即AR = 60/t, t为传粉者的单花访花时间(s)。
1.5 数据统计处理
各居群花性状之间的比较采用单因素方差分析(ANOVA), 然后进行多重比较(t测验, p值进行Bonferroni矫正)。通过各居群主要传粉者的体型大小与花部性状之间的相关性分析(Pearson’s相关检验), 检测二者在空间上的协同变异性。所有数据用R version 2.12.0 (R Development Core Team, 2010)软件程序包进行分析。
2 结果
2.1 不同居群的花部性状比较
各居群的花性状, 包括花大小(花冠长度)、雄蕊杠杆长、冠口高度、柱头高度以及柱头探出距离在居群间表现出显著变异, 结果见表1。相对花结构性状, 花大小在各居群间的变异较小。毛地黄鼠尾草晚花居群的花最大, 花冠长(32.14 ± 0.23) mm (mean ± SE); 圆苞鼠尾草的花最小, 花冠长(30.19 ± 0.37) mm (mean ± SE)。花结构性状中, 柱头探出长度在不同居群间的变异相对较小, 雄蕊杠杆长度、花冠口大小(冠口高)和柱头高度在居群间的变异较大; 其中, 杠杆状雄蕊长度, 圆苞鼠尾草居群最长, 为(5.83 ± 0.06) mm (mean ± SE), 早花毛地黄鼠尾草居中, 为(5.25 ± 0.07) mm, 晚花毛地黄鼠尾草和近掌脉鼠尾草的雄蕊杠杆最短, 分别为(4.55 ± 0.05) mm (mean ± SE)和(4.66 ± 0.08) mm (mean ± SE), 二者差异不显著。
2.2 不同居群的传粉者及其访花行为
本研究4个鼠尾草居群的传粉者均由各类熊蜂组成, 但各居群的传粉者组成、主要传粉者类型及其访花效率表现出很大差异, 结果见表2。毛地黄鼠尾草早花居群的传粉者包括寄生性拟熊蜂(Psithyrus sp.)、熊蜂Bombus lepidus和B. infrequens。寄生性拟熊蜂进行背部传粉(图3D), 在居群中活动最频繁, 访花效率最高, 是该居群的主要传粉者(IVR = 3.94)。熊蜂B. lepidus和B. infrequens的活动频率相对较低, 二者主要进行背部传粉, 其中B. lepidus兼进行腹部传粉。毛地黄鼠尾草晚花居群的传粉者有B. friseanus、 B. infrequens和B. personatus 3种熊蜂。B. friseanus的访花率指数最高(IVR = 2.36), 是该居群主要的传粉者。该居群的3类传粉者中, B. personatus为背部传粉(图3A), 单花访花时间最短, 为(2.55 ± 0.22) s, B. friseanus和B. infrequens以背部传粉为主, 兼进行腹部传粉(图3B、3C), 其单花访花时间是熊蜂B. personatus的6-7倍。近掌脉鼠尾草居群的传粉者种类较多, 常见的有熊蜂B. friseanus和B. personatus, 稀见B. atrocinctus和B. nobilis。B. friseanus在居群中活动最频繁, 兼进行腹部传粉和背部传粉(图3G、3H), 访花率指数在各类传粉者中最高(IVR = 3.84), 是该居群的主要传粉者。圆苞鼠尾草居群的传粉者包括B. personatus、B. friseanus和B. remotes 3种熊蜂。B. personatus进行背部传粉(图3E), 其访花频率和访花效率均最高, 访花率指数为15.30, 是该居群最主要的传粉者。其他2种熊蜂的访花率指数均低于1, 其中B. remotes进行背部传粉, B. friseanus主要进行腹部传粉 (图3F)。
表2 鼠尾草各居群的传粉者组成、体型指标、访花模式和访花效率(平均值±标准误差)
Table 2
| 居群Population | 传粉者 Pollinator assemblage | 传粉者大小 Pollinator’s body size (mm) | 相对频次 Frequency | 单花访花时间 Visit time per flower (s) | 访花率指数 Visitation rate index | 传粉方式 Pollination mode | ||
|---|---|---|---|---|---|---|---|---|
| 体长 Body length | 胸厚 Body thickness | 喙长 Tongue length | ||||||
| 毛地黄鼠尾草I S. digitaloides Population I | ||||||||
| Bombus friseanus † | 15.97 ± 0.55 | 4.97 ± 0.08 | 4.33 ± 0.16 | 0.65 | 15.50 ± 1.92 | 2.36 | D/V | |
| B. personatus | 20.54 ± 0.91 | 5.27 ± 0.06 | 10.71 ± 1.21 | 0.09 | 2.55 ± 0.22 | 2.12 | D | |
| B. infrequens | 15.16 ± 0.76 | 4.40 ± 0.18 | 4.96 ± 0.82 | 0.26 | 17.1 ± 1.23 | 0.91 | D | |
| 毛地黄鼠尾草II S. digitaloides Population II | ||||||||
| Psithyrus sp. † | 23.11 ± 1.41 | 7.43 ± 0.27 | 5.17 ± 0.07 | 0.57 | 8.68 ± 0.90 | 3.94 | D | |
| B. lepidus | 13.55 ± 0.46 | 4.46 ± 0.16 | 3.70 ± 0.37 | 0.20 | 15.57 ± 1.20 | 0.77 | D/V | |
| B. infrequens | 14.78 | 4.46 | 3.02 | < 0.20 | - | - | D | |
| 近掌脉鼠尾草 S. subpalmatinervis | ||||||||
| B. friseanus † | 16.60 ± 0.28 | 5.06 ± 0.12 | 4.49 ± 0.3 | 0.87 | 13.58 ± 0.91 | 3.84 | D/V | |
| B. personatus | 18.76 ± 1.32 | 5.28 ± 0.04 | 10.30 ± 1 | 0.10 | 4.21 ± 0.40 | 1.42 | D | |
| B. atrocinctus | 18.00 ± 0.15 | 5.96 ± 0.15 | 5.38 ± 0.09 | < 0.03 | - | - | D | |
| 圆苞鼠尾草 S. cyclostegia | ||||||||
| B. friseanus | 14.14 ± 0.32 | 4.36 ± 0.16 | 4.44 ± 0.42 | 0.05 | 11.77 ± 0.75 | 0.24 | V/D | |
| B. personatus † | 27.29 ± 0.96 | 7.22 ± 0.09 | 12.49 ± 1.01 | 0.90 | 3.53 ± 0.15 | 15.30 | D | |
| B. remotus | 17.61 ± 0.14 | 6.03 ± 0.08 | 6.29 ± 0.48 | 0.05 | 10.89 ± 1.54 | 0.28 | D | |
D, 背部传粉; D/V, 背部传粉兼有腹部传粉; V, 腹部传粉; V/D, 腹部传粉兼有背部传粉; †, 居群的主要传粉者; -, 无相关数据。
D, dorsal pollination; D/V, dorsal pollination prevails over ventral pollination; V, ventral pollination; V/D, ventral pollination prevails over dorsal pollination; †, main pollinator of population; -, no data measured.
2.3 各居群主要传粉者的体型大小与花部性状的协同变异
本研究的4个居群间, 主要传粉者的体型大小与花部性状表现出不同程度的协同变异(图2)。各居群主要传粉者的体长与花冠长显著负相关(t = -6.23, r = -0.97, p = 0.024, 图2A), “体长+喙长”与花冠长表现出近似显著的负相关(t = -4.13, r = -0.94, p = 0.053, 图2中未展示); 然而, 主要传粉者的体长与雄蕊杠杆长表现出极显著的正相关(t = 14.48, r = 0.99, p = 0.004, 图2B)。另外, 早花毛地黄鼠尾草和圆苞鼠尾草2个居群, 其主要传粉者的胸厚显著大于其他2个居群(p < 0.001), 相应地这2个居群的花冠口高和柱头高度也显著大于其他2居群(表1; 图2 C、2D)。
图2
图2
花部性状与主要传粉者体型大小在居群间的变异关系。A, 花冠长与传粉者体长的变异关系(r = -0.97, p = 0.024)。B, 雄蕊杠杆长与传粉者体长的变异关系(r = 0.99, p = 0.004)。C, 花冠口高与传粉者胸厚的变异关系(r = 0.92, p = 0.08)。D, 柱头高度与传粉者胸厚的变异关系(r = 0.89, p = 0.10)。
Fig. 2
Variation relationship of floral traits to body size of main pollinator’s among populations. A, relationship between corolla length and pollinator’s body length (r = -0.97, p = 0.024). B, relationship between staminal lever length and pollinator’s body length (r = 0.99, p = 0.004). C, relationship between corolla entrance height and pollinator’s body thickness (r = 0.92, p = 0.08). D, relationship between stigma height and pollinator’s body thickness (r = 0.89, p = 0.10).
图3
图3
鼠尾草各居群不同传粉者的传粉模式。毛地黄鼠尾草(干河坝)居群I: 背部传粉(A、C)和腹部传粉(B); 毛地黄鼠尾草(甘海子)居群II: 背部传粉(D); 圆苞鼠尾草居群: 背部传粉(E)和腹部传粉(F); 近掌脉鼠尾草居群: 背部传粉(G、I)和腹部传粉(H)。
Fig. 3
Pollination modes of different pollinators in each population of Salvia. Population I of S. digitaloides in Ganheba: dorsal pollinations by bigger Bombus friseanus (A) and B. personatus (C), and ventral pollinations by smaller B. friseanus (B); population II of S. digitaloides in Dongbagu: dorsal pollination by Psithyrus sp. (D); population of S. cyclostegia: dorsal pollinations by B. personatus (E) and ventral pollinations by smaller B. friseanus (F); population of S. subpalmatinervis: dorsal pollinations by bigger B. friseanus (G) and B. personatus (I), and ventral pollinations by smaller B. friseanus (H).
3 讨论
3.1 鼠尾草不同居群的主要传粉者及其传粉模式
Stebbins (1970)提出, 在居群中活动相对最频繁和最有效的传粉者是花部特征进化最重要的选择压力, 即有效传粉者原则(most effective pollinator principle)。本研究用访花率指数(IVR)综合了传粉者的访花频率和访花效率, 并以其作为居群主要传粉者的评判指标。结果表明, 各居群的主要传粉者均为居群中活动最频繁(即访花频率最高)的访花者。圆苞鼠尾草居群中, 熊蜂B. personatus的活动频率和访花效率在所有传粉者(pollinator assemblage)中均占绝对优势, 是该居群最主要的传粉者(IVR = 15.3)。然而, 近掌脉鼠尾草和晚花毛地黄鼠尾草2个居群, 尽管其主要传粉者B. friseanus在居群中活动频繁、访花率指数最高, 但是访花效率(如单位时间的访花数)远低于同居群的熊蜂B. personatus。本研究中, 访花率指数仅从访花速率(或数量)的角度考虑了传粉者的传粉效率, 而并未考虑传粉质量的高低。例如传粉者-花结构的相互匹配性可引起单次访花的花粉移出(pollen removal)和花粉沉积(pollen deposition)量的差异, 传粉者访花忠实性(floral constancy)可降低异种花粉的干扰、提高传粉效率(Darwin, 1876; Gegear & Laverty, 2001; Zhang et al., 2011)。一些研究表明, 居群中活动最频繁的访花者通常具有较低的传粉效率; 相反, 较为稀见的访花者可能是有效的传粉者(Armbruster, 1985; Tandon et al., 2003; Fenster et al., 2004)。但是, 另一些研究表明居群中活动最频繁的访花者同样是最有效的传粉者(Fishbein & Venable, 1996; Olsen, 1997; Fenster & Dudash, 2001)。
鼠尾草的雄蕊杠杆传粉机制, 传粉者反复触发杠杆运动的过程满足花粉分发机制(Harder & Thomson, 1989), 被认为具有花粉分发功能(pollen partitioning) (Reith et al., 2007), 在一定程度上是对具有较高花粉浪费行为的蜂类传粉的适应。本研究的4个鼠尾草居群, 每个居群均表现出两类传粉模式。一类是背部传粉, 是各居群内的主要传粉方式, 传粉者是体型相对较大的熊蜂, 如B. personatus、 B. infrequens和B. lepidus; 另一类是腹部传粉, 传粉者主要是小体型的B. friseanus熊蜂。各类传粉者尽管访花行为完全不同, 但其目的主要为获取花蜜。大体型熊蜂访花时, 可正面推动杠杆运动, 将花粉精确地投置在其背部。此类传粉者吸取花蜜后, 退离花冠, 其背部的花粉不会碰触其他花结构, 同时传粉者自身也无法触及和梳理花粉, 从而避免了花粉浪费(张勃等, 2010)。然而, 小体型熊蜂访花时, 因体力太小无法正面推动杠杆运动, 不得不“倒挂式”仰卧进入花冠, 从而带动杠杆上臂向下翻转将花粉落置在腹部。因这类小传粉者访花时完全进入花冠, 吸取花蜜离开花冠时, 通过操弄花结构会造成大量花粉浪费; 更主要的是传粉者腹部携带花粉, 当在花间运动时, 大部分花粉将会掉落, 造成浪费。因此, 从植物进化的角度, 大体型传粉者所进行的背部传粉仍然是最合法的传粉方式; 而腹部传粉是雄蕊杠杆机制筛选小体型次要传粉者的“副产品”。
3.2 不同居群花部性状与传粉者互作的空间变异
许多研究表明, 当一个居群内存在传粉效力不同的几种传粉者类群时, 传粉相关性状将受各类传粉功能群的净选择压而进化, 最终可能会导致对某一功能群的专化适应(Schemske & Horvitz, 1989; Aigner, 2001; Mitchell et al., 2009)。本研究结果表明, 4个鼠尾草居群的花大小以及花结构性状对各自主要传粉者的体型大小表现出明显的进化响应。例如, 花冠长与传粉者的体长(或体长+喙长)之间表现出显著的负相关(r = -0.97, p = 0.02), 长花冠居群主要传粉者的体型较短; 相反, 短花冠居群主要传粉者的体型较长。这一结果似乎与传统上长花冠配长口器的协同进化模式相悖(Darwin, 1862; Whittall & Hodges, 2007; Pauw et al., 2009)。观察发现, 在雄蕊杠杆传粉互作系统中, 体型相对较大的传粉者访问花冠相对较长的花时, 因受花冠口限制而无法完全进入冠内吸取花蜜, 因此会影响传粉与繁殖成功; 相反, 体型相对较大的传粉者访问花冠相对较短的花时, 不仅有利于传粉者吸食花蜜, 而且传粉者可处于花冠口合适的位置, 便于花粉承载与精确传粉。本研究4个居群的花冠口高度对各自主要传粉者胸厚的进化响应进一步支持了这一观点。例如, 传粉者体型较大的早花毛地黄鼠尾草和圆苞鼠尾草居群, 其花冠口高度显著大于小体型传粉者的其他2个居群, 但是, 2个大体型传粉者居群的花冠口高度明显小于各自传粉者的胸厚(冠口高: (6.02 ± 0.10) mm和(6.48 ± 0.10) mm; 传粉者胸厚: (7.43 ± 0.27) mm和(7.22 ± 0.09) mm); 然而, 小体型传粉者的2个居群其花冠口高度略大于传粉者的胸厚(花冠口高: (5.30 ± 0.05) mm和(5.37 ± 0.07) mm; 传粉者胸厚: (4.97 ± 0.08) mm和(5.06 ± 0.12) mm)。因此, 相对较短的花冠和较小的花冠口在一定程度上是对大体型传粉者的适应。
鼠尾草雄蕊杠杆传粉机制被认为是一精确传粉系统(Claßen-Bockhoff et al., 2004b; 张勃等, 2010)。在该传粉系统中, 雄蕊杠杆长度决定着传粉者在其背部承载花粉的位置; 相应地, 当柱头的空间位置与花粉的承载部位相匹配时, 精确传粉才能实现。本研究发现, 4个居群主要传粉者的体长与雄蕊杠杆长度表现出高度的协同变异性(r ≈ 1, p < 0.01), 同时柱头高度与传粉者的胸厚也表现出很好的匹配性。例如传粉者体型较大的2个居群(早花毛地黄鼠尾草和圆苞鼠尾草居群), 其柱头高度相应地大于其他2个小体型传粉者的居群。这一结果充分说明杠杆状雄蕊在该传粉系统中发挥的关键作用及其在进化过程中表现出的高度的可塑性, 即对传粉环境空间变异的敏感的进化响应。同时, 这一结果也为“杠杆状雄蕊作为激发鼠尾草属物种适应辐射的关键性状”的假说提供了一定的支持。
4 结论
本研究的鼠尾草属3个物种4个居群, 其传粉者物种组成、主要传粉者类型以及传粉者体型大小表现出很大的空间变异性; 相应地, 各居群的雄蕊杠杆传粉相关花性状, 包括花冠长、雄蕊杠杆长度、花冠口大小和柱头位置对各自的主要传粉者表现出明显的进化响应。每个居群中, 不同体型大小的传粉者总体表现出背部传粉和腹部传粉2种传粉方式, 但背部传粉机制仍是塑造花性状进化的最有效传粉方式; 居群中传粉效率相对较低的传粉者类群, 可通过其高频率的访花行为作为主要传粉者施加选择压, 塑造花性状的进化。杠杆状雄蕊以及相关花性状对传粉环境变异敏感的进化响应, 充分说明雄蕊杠杆机制在鼠尾草属植物传粉系统中发挥的关键作用及其在进化上高度的可塑性, 这将有利于促进该属物种的适应辐射。
致谢
甘肃农业大学草业学院青年教师科研启动项目(CY-QN200603)和中国科学院“百人计划”项目资助; 感谢中国林业科学院资源与昆虫研究所谢正华博士鉴定传粉昆虫标本;感谢中国科学院西双版纳热带植物园李庆军研究员对本研究给予的指导和帮助。
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