傳粉者偏好及競爭對台灣不同海拔植物花色組成的影響

Abstract

台灣原生被子植物接近4 千種，推測至少2/3 以上靠昆蟲傳粉，而花色在昆蟲對植物的偵測上扮演重要角色。由於台灣低中高海拔截然不同的生態環境會導致傳粉者在組成上有較大差異，而不同傳粉者的先天偏好會對當地植物的花色組成有潛在影響。同時，傳粉者介導的競爭機制亦會影響被子植物的花色。然而實際對台灣原生被子植物的花色研究卻十分有限。本研究大規模採集了台灣低，中，高海拔合共727 種原生被子植物的花色反射光譜，并利用蜜蜂視覺空間模型和蜜蜂視覺識別曲線擬合模型進行分析。我們發現台灣低海拔地區(<900 m)的物種相較於中(1500-2200 m)，高(> 2850 m)海拔地區，擁有更高的花色多樣性，低海拔物種在蜜蜂視覺空間模型中佔據的最小凸多邊形(mcp)面積為0.546，大於中，高海拔物種花色所佔的面積(0.270 和0.304)。並且一部分只出現在低海拔的花色，其物種的潛在傳粉者在中，高海拔少有分佈。藉此可以推測由海拔上升介導的傳粉者多樣性下降，會對不同海拔的花色組成產生影響。我們亦發現台灣中，高海拔地區的花色整體上和蜜蜂視覺識別能力更為吻合，表明蜂類昆蟲對於中，高海拔的花色組成具有更重要的影響，亦是中高海拔被子植物最重要的傳粉者之一。此外，高海拔物種的花色在蜜蜂視覺空間模型中趨於分散(p=0.060)，而中，低海拔物種的花色並無分散趨勢 (p=0.599, p=0.040)。物種間親緣關係指數(Mean Pair-wise Phylogenetic Distance)分析的結果表明，高海拔物種的系統發育結構趨於聚集，並且台灣原生被子植物的花色具有較弱的系統發育信號(Phylogenetic signal, Blomberg’s K)。我們由此推測台灣高海拔物種的花色趨於分散，可能是親緣關係較近的植物對於競爭有限傳粉者的 適應性結果。本研究首次站在傳粉者視覺對台灣原生被子植物的花色多樣性進行探討，對未來有關被子植物花色演化及植物-傳粉者交互作用的研究有較大助益。

A Classic view asserted that floral color assembly could be shaped by the pollinator preference. However, the floral color assembly could be alternatively explained by competition for pollinators they shared. Here, we analyzed the floral color assembly from low altitude to alpine region in a subtropical island Taiwan, through the bee perceptual color space, in an effort to evaluate whether these two models could compatibly account for the floral color assembly along altitudes. We found that the diversity of the floral colors in middle (1500-2200 m) and high altitudes (over 2850 m) were significantly lower than that of low altitude regions (below 900 m), which could be partly explained by the declined abundance of pollinators with increasing altitudes. Moreover, the chromatic signals of the alpine species most fit with the discrimination ability of bees’ vision, which suggested that bees might be the most important pollinator in the subtropical alpine regions. In addition, the alpine species exhibited larger divergence of the floral colors than expected by chance, but no similar trends were observed in low and middle altitude. When considering phylogenetic structure, sympatric alpine species tend to be phylogenetically related (clustering) but floral colors of related species tend to be diverse (weak phylogenetic signal). This suggested that the over-dispersion of floral color among related alpine species may be the result of their competition for limited pollinators. Overall, our results first demonstrated that the floral color assembly along altitudes in a subtropical island could respectively adapted to the pollinator preference model and competition mode.