Fixed Differences in the paralytic Gene Define Two Lineages within the Lutzomyia longipalpis Complex Producing Different Types of Courtship Songs

The sand fly Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae), the most important vector of American visceral leishmaniasis, is widely distributed in Latin America. There is currently a consensus that it represents a species complex, however, the number and distribution of the different siblings is still uncertain. Previous analyses have indicated that Brazilian populations of this vector can be divided into two main groups according to the type of courtship song (Burst vs. Pulse) males produce during copulation. Nevertheless, no diagnostic differences have been observed between these two groups with most molecular markers used to date. We analyzed the molecular divergence in a fragment of the paralytic (para) gene, a locus involved in the control of courtship songs in Drosophila, among a number of Lu. longipalpis populations from Brazil producing Burst and Pulse-type songs. Our results revealed a very high level of divergence and fixed differences between populations producing the two types of songs. We also compared Lu. longipalpis with a very closely related species, Lutzomyia cruzi, which produces Burst-type songs. The results indicated a higher number of fixed differences between Lu. cruzi and the Pulse-type populations of Lu. longipalpis than with those producing Burst-type songs. The data confirmed our previous assumptions that the presence of different sibling species of the Lu. longipalpis complex in Brazil can be divided into two main groups, one representing a single species and a second more heterogeneous group that probably represents a number of incipient species. We hypothesize that para might be one of the genes directly involved in the control of the courtship song differences between these two groups or that it is linked to other loci associated with reproductive isolation of the Brazilian species.长须罗蛉（Lutzomyia longipalpis，双翅目：毛蠓科：白蛉亚科）是美洲内脏利什曼病（American visceral leishmaniasis）最为重要的传播媒介，广泛分布于拉丁美洲。目前学界已普遍认可其隶属于一个物种复合体（species complex），但不同姊妹种的数量与分布仍未明确。 既往分析表明，依据该媒介昆虫在交配过程中雄虫产生的求偶歌（courtship song）类型，可将巴西境内的种群划分为两大类群：爆发型（Burst）与脉冲型（Pulse）。然而，截至目前所用的多数分子标记（molecular markers）均未在这两类群间检测到诊断性差异。 我们针对巴西境内两类求歌类型（爆发型与脉冲型）的长须罗蛉种群，对麻痹基因（paralytic，para）的一段片段开展了分子分化分析——该基因位点在果蝇（Drosophila）中参与调控求偶歌的表达。 结果显示，两类求歌类型的种群间存在极高水平的分子分化与固定差异（fixed differences）。我们还将长须罗蛉与亲缘关系极近的克鲁兹罗蛉（Lutzomyia cruzi，其雄虫产生爆发型求偶歌）进行了比较，结果表明：相较于爆发型长须罗蛉种群，克鲁兹罗蛉与脉冲型长须罗蛉种群间存在更多的固定差异。 本研究数据证实了我们此前的假设：巴西境内长须罗蛉物种复合体的不同姊妹种可划分为两大主要类群，其中一类代表单一物种，另一类则更为异质，可能包含多个处于物种形成初期的类群。我们推测，麻痹基因（para）可能直接参与调控这两类群间的求偶歌差异，亦或与巴西境内该类物种的生殖隔离（reproductive isolation）相关位点存在连锁。