- 學位論文
黃果蠅與擬黃果蠅間生殖隔離的遺傳分析
Genetic analysis of reproductive isolation between Drosophila melanogaster and D. simulans
摘要
雜交後代的不孕或死亡的雜交不親合與行為上的隔離避免種族之間基因交流障礙是造成生殖隔離及種化的關鍵。黃果蠅與擬黃果蠅是僅在兩到三百萬年前左右分化，親緣關係很近的兩個種族，很少會有交配行為的發生。若黃果蠅的雌性與擬黃果蠅的雄性雜交只能產生存活的不孕雌性成蟲，雜交雄性則在幼蟲時期死亡。在相反方向的雜交，則只能產生不孕的雄性成蟲，雜交雌性則在胚胎時期死亡。根據附屬X染色體品系的研究，顯示雜交雌性的死亡是由於黃果蠅的X染色體與擬黃果蠅的母系產物不相容所造成。為了確認有參與雜交不親合的X染色體區段，我們系統性的利用黃果蠅Y染色體帶有多一段X染色體的基因重複 (gene duplication)並且帶有Zhr的品系來篩選。我篩選22個基因重複的品系涵蓋了97.22%的X染色體，結果顯示其中有三個X染色體重複的片段顯著造成雜交雄性的死亡。根據此結果指出在黃果蠅X染色體上至少有三個區域上有基因造成黃果蠅與擬黃果蠅雜交不親合。為了瞭解基因影響行為上隔離的機制，我利用EMS突變黃果蠅，試著找出影響雄果蠅改變求偶行為並讓雌性擬黃果蠅接受的基因。結果我篩選出的突變果蠅有增加對異族雌果蠅的求偶。
並列摘要
Hybrid incompatibility (HI) and behavioral isolation in the forms of hybrid lethality or sterility are important barriers to prevent gene flow among species that may encounter each other, causing reproductive isolation and thus lead to speciation. The closely related Drosophila species, D. melanogaster and D. simulans, rarely mate each in nature despite diverging 2-3 million years ago. The cross between D. melanogaster females and D. simulans males produces sterile F1 females and males died at larval stage. The reciprocal cross yields sterile F1 males and embryonic lethal females. Using attached-X chromosome strains, it is proposed that the hybrid female lethality is caused by the presence of D. melanogaster X chromosome (Xm) and maternal product from D. simulans. To identify loci which contribute to the hybrid lethality, I conducted a genetic screen by crossing D. simulans females to males of the D. melanogaster X chromosome duplication lines that contain an extra X fragment on Y chromosomes in Zhr background. I have screened 22 lines covering 97.22 % of the X chromosome, and the results show that three of the 22 duplications have significant effect on hybrid male lethality. My results indicated that there are at least three regions on the Xm chromosome contributing to HI between D. melanogaster and D. simulans. To identify the genes responsible for the behavioral isolation between these sibling species, I used EMS mutagenesis to mutagenize D. melanogaster males to identify genes affecting male behaviors responsive to the acceptance by D. simulans females. The results indicated that the mutant lines we chose spending more time courtship heterospecific females.