台灣特有常綠杜鵑亞屬物種的適應分歧

Abstract

臺灣的地形呈現豐富的海拔梯度變化，此一海拔梯度差異所產生的多樣化環境，提高了廣適性物種的族群破碎分佈到不同海拔而產生遺傳分化與在地適應，甚至最終導致族群間產生生殖隔離而促成新物種的產生。然而另一方面高低海拔族群間，可能受限於地理隔離不足而仍能基因交流，進而抑制族群間的分化。因此，在臺灣間斷分佈的杜鵑便提供了探討適應性演化抗衡族群間基因交流以建立生殖隔離，最終產生新品種的絕佳素材。杜鵑花科的玉山杜鵑複合群包含四種杜鵑，其中紅星杜鵑局限分佈於低海拔，其餘三種（玉山杜鵑、森氏杜鵑、南湖杜鵑）則局限分佈於較高的海拔。本研究以擴增片段長度多態性（AFLP）分子標記獲得四種杜鵑（9個族群、172個個體）之變異。 為了評估玉山杜鵑複合群的族群結構與遺傳距離，我們採用STRUCTURE和DAPC分析AFLP分子標記基因座，幫助我們瞭解各種間的遺傳差異。為了評估環境差異是否對玉山杜鵑複合群的遺傳變異產生影響，表示有適應性演化的發生，我們使用ARLEQUIN和BAYESCAN對種間遺傳變異做離群檢測找出偏離中性演化的基因座。而為了評估環境變量對玉山杜鵑複合群的影響，我們使用PCA分析族群間的環境因數差異性，並通過相關性檢測篩選出共線性較低的六個環境因子。然後以RDA分析遺傳變異、族群分群和環境因子之間的關聯性。最後使用SAMBADA的邏輯回歸來檢測偏離中性演化的基因座頻率和這些族群間有差異的環境變數之間的關聯性，以確定那些環境因數可能和適應性演化有關。 STRUCTURE和DAPC分析一致顯示紅星杜鵑與玉山杜鵑複合群內的另外三種杜鵑之間具有最大的種間遺傳差異。Outlier loci檢測到六個顯著偏離中性演化的基因座。環境因子做PCA分析發現與溫度相關的環境因子相較於雨量而言，可以更好的將紅星杜鵑和其他三個物種的生育環境做區分。RDA分析證明六個相關性較低的環境因子中（BIO01、BIO04、BIO13、BIO18、BIO19、BIO20）三個與溫度相關的環境因子（BIO01、BIO04、BIO20）在區分紅星杜鵑和其他三個物種間貢獻了主要力量。SAMBADA的分析結果也顯示六個偏離中性演化的位點中有五個檢測出與溫度相關的環境因子存在較大的關聯性。 總結發現，紅星杜鵑和玉山杜鵑複合群內的其他三個種隨著海拔梯度的變化呈現遺傳分化和環境差異，且檢測出偏離中心演化的基因座和環境因子具有關聯性。因此，我們認為紅星杜鵑已經發生了適應性分化，應該將其從玉山杜鵑複合群中獨立出來。另外，南湖杜鵑雖然形態上和複合群內的其它三個種有所差異，但遺傳分析並不支持南湖杜鵑與複合群內的其它三個種有最大的遺傳距離，所以本研究不認同南湖杜鵑歸為亞屬里不同的種。

Taiwan has dramatic elevation gradient changes of terrain, and the altitudinal gradients of diversified environment may lead to the increased opportunities for local adaptation of different ecotypic species. Populations distributed at different altitudes may encounter reproductive isolation and even speciation. Rhododendron pseudochrysanthum complex (Ericaceae) includes four species. Among them, Rhododendron rubropunctatum is restricted to low elevation and the other three (Rhododendron morii, Rhododendron pseudochrysanthum, Rhododendron hyperythrum) are restricted to higher elevations. We used amplified fragment length polymorphism (AFLP) technique to quantify the genetic variation and divergence of 172 individuals from nine populations of R. pseudochrysanthum complex. In order to evaluate genetic structure and genetic differentiation of the R. pseudochrysanthum complex, STRUCTURE and DAPC were used to infer genetic composition of R. pseudochrysanthum complex. To detect genetic loci deviated from neutral evolution, we used ARLEQUIN and BAYESCAN to detect the outlier loci. To evaluate the suitable whether environmental factors variation among species in R. pseudochrysanthum complex, we applied PCA analysis the environmental factors among different populations. Further, to co-evaluate the Association between genetic data and environmental variables, we applied RDA to study correlation among genetic data, population data and environmental variables. Finally, we used SAMBADA to assess the correlation between outlier loci and environmental variables to examine whether local adaptation signal exist among these outlier loci. Both DAPC and STRUCTURE showed that R. rubropunctatum formed its own cluster within R. pseudochrysanthum complex. Outlier loci analysis detected six loci that deviated from neutral selection. PCA and RDA portrayed that environment factor of R. pseudochrysanthum complex can be diversified into two groups. SAMBADA results showed that the outlier loci were significantly correlated with the environmental factors about temperature. In conclusion, according to the genetic data and environmental variables analysis, R. rubropunctatum has the local adaptation in R. pseudochrysanthum complex, We proposed that the R. rubropunctatum may be phylogenetically separated from R. pseudochrysanthum complex. In addition, although the R. hyperythrum is morphologically different from the other three species in R. pseudochrysanthum complex, but the genetic analysis does not support the maximum genetic distance between the R. hyperythrum and the other three species in the complex. So this study doesn't support that the R. hyperythrum belong to the Hymenanthes subgenus’s Ponica subsection.