A mosquito sperm's journey from male ejaculate to egg: Mechanisms, molecules, and methods for exploration

Abstract

SUMMARYThe fate of mosquito sperm in the female reproductive tract has been addressed sporadically and incompletely, resulting in significant gaps in our understanding of sperm‐female interactions that ultimately lead to fertilization. As with other Diptera, mosquito sperm have a complex journey to their ultimate destination, the egg. After copulation, sperm spend a short time at the site of insemination where they are hyperactivated and quickly congregate near the entrance of the spermathecal ducts. Within minutes, they travel up the narrow ducts to the spermathecae, likely through the combined efforts of female transport and sperm locomotion. The female nourishes sperm and maintains them in these permanent storage organs for her entire life. When she is ready, the female coordinates the release of sperm with ovulation, and the descending egg is fertilized. Although this process has been well studied via microscopy, many questions remain regarding the molecular processes that coordinate sperm motility, movement through the reproductive tract, maintenance, and usage. In this review, we describe the current understanding of a mosquito sperm's journey to the egg, highlighting gaps in our knowledge of mosquito reproductive biology. Where insufficient information is available in mosquitoes, we describe analogous processes in other organisms, such as Drosophila melanogaster, as a basis for comparison, and we suggest future areas of research that will illuminate how sperm successfully traverse the female reproductive tract. Such studies may yield molecular targets that could be manipulated to control populations of vector species. Mol. Reprod. Dev. 83: 897–911, 2016. © 2016 The Authors. Molecular Reproduction and Development Published by Wiley Periodicals, Inc.

fruitless mutant male mosquitoes gain attraction to human odor

“…Because fruitless plays a key role in male courtship and mating in Drosophila, we asked if it is similarly required in Aedes aegypti. Since mosquitoes show extremely rapid in-flight mating behavior that is difficult to observe or quantify 44 , we used previously developed insemination assays 45,46 to quantify the ability of males to successfully mate ( Fig. 2g).…”

“…For each trial, 10 female Liverpool-IB12 virgin mosquitoes were crossed to 11 virgin male mosquitoes of either Liverpool-IB12 or fruitless ∆M/ fruitless ∆M-tdTomato genotype in a bucket cage for 24 hr, with access to 10% sucrose. Mosquitoes were then anesthetized at 4ºC, females separated from males, and female spermathecae were dissected to score for insemination as a sign of successful mating 46 . Control virgin females were dissected in parallel to verify absence of insemination.…”

Sex specific molecular responses of Quick-To-Court in Indian malarial vectorAnopheles culicifacies: conflict of mating and/or blood feeding?

“…Available literature suggests that most anopheline mosquitoes mating behavioural activities commenced at the onset of sunset, usually at 17:00 pm which may continue till 20:00 pm [29,[32][33]. We hypothesize that if true, the transcriptional modulation of Ac-qtc in response to dawn/dusk cycle, must have functional correlation with the mating success, especially insemination events where adult females receive and store the sperms in her spermethecae delivered by male during copulation [34]. To test this idea, first we identified two sperm specific transcripts from the draft genome of the mosquito A. culicifacies, using (ams & mts) as query sequences, previously characterized from A. gambiae [26].…”

Structural variation in Drosophila melanogaster spermathecal ducts and its association with sperm competition dynamics

“…However, it is conceivable that SDPs are modified, either by the female-or male-derived products, after the first mating in a way that restricts the entry of second male sperm into the spermathecae, but not the release of sperm that are already stored. This change could, for example, lead to SDPs disrupting mechanisms used to recruit sperm from the bursa, such as the release of chemoattractants or pressure changes that draw sperm into the spermathecal capsule [28].…”