Abstract
BackgroundThe male reproductive system of insects can have several tissues responsible for the secretion of seminal fluid proteins (SFPs), such as testes, accessory glands, seminal vesicles, ejaculatory duct and ejaculatory bulb. The SFPs are transferred during mating and can induce several physiological and behavioral changes in females, such as increase in oviposition and decrease in sexual receptivity after copulation. The phlebotomine Lutzomyia longipalpis is the main vector of visceral leishmaniasis. Despite its medical importance, little is known about its reproductive biology. Here we present morphological aspects of the male L. longipalpis reproductive system by light, scanning and transmission electron microscopy, and compare the mating frequency of both virgin and previously mated females.ResultsThe male L. longipalpis reproductive system is comprised by a pair of oval-shaped testes linked to a seminal vesicle by vasa deferentia. It follows an ejaculatory duct with an ejaculatory pump (a large bulb enveloped by muscles and associated to tracheas). The terminal endings of the vasa deferentia are inserted into the seminal vesicle by invaginations of the seminal vesicle wall, which is composed by a single layer of gland cells, with well-developed endoplasmic reticulum profiles and secretion granules. Our data suggest that the seminal vesicle acts both as a spermatozoa reservoir and as an accessory gland. Mating experiments support this hypothesis, revealing a decrease in mating frequency after copulation that indicates the effect of putative SFPs.ConclusionUltrastructural features of the L. longipalpis male seminal vesicle indicated its possible role as an accessory gland. Behavioral observations revealed a reduction in mating frequency of copulated females. Together with transcriptome analyses from male sandfly reproductive organs identifying ESTs encoding orthologs of SFPs, these data indicate the presence of putative L. longipalpis SFPs reducing sexual mating frequency of copulated females.
Highlights
The male reproductive system of insects can have several tissues responsible for the secretion of seminal fluid proteins (SFPs), such as testes, accessory glands, seminal vesicles, ejaculatory duct and ejaculatory bulb
Scanning Electron Microscopy (SEM) Male adults of 0–6 h after emergence were sedated for 2 minutes in dried CO2 atmosphere, dissected and the reproductive organs were fixed by immersion for at least 2 hours in 2.5% glutaraldehyde diluted in 0.1 M sodium cacodylate buffer
The reproductive system of L. longipalpis males is formed by a pair of oval-shaped testes, each one measuring about 80 mm long640 mm wide
Summary
The male reproductive system of insects can have several tissues responsible for the secretion of seminal fluid proteins (SFPs), such as testes, accessory glands, seminal vesicles, ejaculatory duct and ejaculatory bulb. The sandfly Lutzomyia longipalpis (Lutz & Neiva, 1912) is a species complex [1] and is considered the main vector of visceral leishmaniasis in the New World [2]. This blood-sucking insect is a fascinating model for studies on reproductive behavior as its males form leks on or near hosts [3], releasing sex/aggregation pheromones [4,5] and producing acoustic signals during copulation [4,6] that probably play a role in the sexual isolation of different sibling species, as the different species produce diverse combinations of them [1]. Studies on the morphology and ultrastructure of internal reproductive organs and spermatozoa in insects offer an important tool in phylogenetic analysis at different taxonomic levels [9,10]
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