| Summary: | <p>Abstract</p> <p><it>Lutzomyia longipalpis s.l</it>. (Diptera: Psychodidae) is the principal vector of <it>Leishmania infantum chagasi </it>in the Americas, and constitutes a complex of species. Various studies have suggested an incipient speciation process based on behavioral isolation driven by the chemotype of male sexual pheromones. It is well known that natural barriers, such as mountains and rivers can directly influence population divergence in several organisms, including insects. In this work we investigated the potential role played by the Sao Francisco River in eastern Brazil in defining the current distribution of <it>Lu. longipalpis s.l</it>. Our studies were based on analyses of polymorphisms of the <it>cytochrome b </it>gene (<it>cyt b</it>) sequences from <it>Lu. longipalpis s.l</it>. available in public databases, and from additional field-caught individuals. Altogether, 9 distinct populations and 89 haplotypes were represented in the analyses. <it>Lu. longipalpis s.l</it>. populations were grouped according to their distribution in regards to the 10°S parallel: north of 10°S (<10°S); and south of 10°S (>10°S). Our results suggest that although no polymorphisms were fixed, moderate genetic divergences were observed between the groups analyzed (i.e., <it>F</it><sub><it>ST </it></sub>= 0.184; and <it>Nm </it>= 2.22), and were mostly driven by genetic drift. The population divergence time estimated between the sand fly groups was about 0.45 million years (MY), coinciding with the time of the change in the course of the Sao Francisco River, during the Mindel glaciation. Overall, the polymorphisms on the <it>cyt b </it>haplotypes and the current speciation process detected in <it>Lu. longipalpis s.l</it>. with regards to the distribution of male sexual pheromones suggest a role of the Sao Francisco River as a significant geographical barrier in this process.</p>
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