黃果蠅的行為隔離

Abstract

族群間的行為隔離被認為是初期種化的過程之一。住昔研究顯示黃果蠅在辛巴威 (Z型) 與其他大陸 (M型) 的族群中有明顯的行為隔離：Z型雌果蠅偏好與Z型雄果蠅交尾，而M型雌性則無強烈的偏好性。為了瞭解Z型行為地理上的分布及ZM交配模式的遺傳基礎，我以多重選擇測試了21個來自非洲、歐洲及北美州等族群，共141個品系的雌蟲擇偶偏好性與雄蟲交尾成功率。結果與先前的發現一致，歐美品系皆為M型，非洲族群則有明顯的Z型多態性，且大部分品系表現高至中等的Z型偏好性 (Z型及中間型)。Z型品系主要出現在東非裂谷周邊的東非及南非族群中，相對弱偏好性的品系則出現在西非及衣索比亞族群，環境因子的相關性結果表示，雌蟲擇偶偏好性與經度、緯度和濕度有關，雄蟲交尾成功率與經度有關。此外，ZM型的交配速度、基因體組混和比例和Desaturase 2基因的關聯性亦於此篇研究討論。每五分鐘各配對型的對數紀錄結果表現在一定時間內M型的交配速度快於Z型。比較各品系的基因體組中非非洲比例與ZM型的多態性，發現大部分的Z型品系有較低的非非洲比例。以及過去實驗認為與Z型雌蟲擇偶偏好性有高相關的Desaturase 2基因，同樣的在我的大族群樣本數中，表現出了插入型比缺失型的有更高表現的交配偏好性與成功率。這項以大量非洲族群樣本進行詳細行為隔離分析的研究提供了未來進一步遺傳分析的基礎。

Behavioral isolation among different populations is considered as a process of incipient speciation. Previous studies suggested that behavioral isolation existed between Zimbabwean (Z race) and other continental (M race) populations of Drosophila melanogaster. When given a choice, Z females preferred to mate with Z males, whereas M females mated with males of both races with little discrimination. To reveal the geographical distribution and the genetic basis of ZM races, I examined the female preference and male mating success of 141 lines from 21 localities, including Africa, Europe, and North America, by multiple-choice cage experiments. The results showed that cosmopolitan lines behaved M type, and African lines behaved an extensive polymorphism on both female preference and male mating success. As the initial discovery in Zimbabwean population, most of African lines displayed strong to intermediate Z female preference and male mating success. The highest frequency of Z behavior was present in the southern and eastern Africa around the Great Rift Valley, and the weakest Z-like behavior was present in western Africa and Ethiopia. The correlation between Z behavior and environmental factors showed that the Z-femaleness was correlated to latitude, longitude, and precipitation, and the Z-maleness was correlated to longitude. The ZM behavior is also associated with mating speed, genomic admixture, and Desaturase 2 (Desat2) genotype. In behavioral experiments, the pairs of each mating types of each time interval revealed that M lines mate faster than strong Z lines. By comparing the non-African admixture proportion of African lines and the behavioral polymorphism, the data revealed that most Z lines have limited non-African admixture. The association between the ZM behavior and the allele variation of Desat2 showed similar results in an earlier study that the lines carrying the insertion allele tended to exhibit higher mating preference and success than that carrying the deletion allele did. This detailed behavioral isolation study with large population samples provides a wide-range of phenotypic variation for further genetic mapping.