A mosquito's sperm may have its own "sense of smell."
Researchers found specialized chemical sensors dubbed "odorant receptors" (ORs) in the sperms' tails. These sensors are the same as those that are located in the olfactory system on the insects' antennae, a Vanderbilt University news release reported.
"This discovery is really out of the box for us," L.J Zwiebel, the Cornelius Vanderbilt Chair in Biological Sciences who directed the study said in the news release. "It is the first time that insect ORs have been found to function in non-sensory cells or tissue. We think this could be an entirely new paradigm for how insect reproduction is regulated. If it is, it could provide a powerful new approach for controlling populations of insects of medical and/or economic importance."
Female mosquitos only mate once in their lives, they then store the male's sperm in an organ called the spermathecae. After the female mates she must indulge in a blood meal in order to produce eggs; this is why the females bite humans and animals. Once the eggs are developed they are fertilized by the stored sperm.
"The sperm may need a chemical signal to become ready for fertilization," Research Assistant Professor Jason Pitts said in the news release. "There are reports that within one day after insemination, the sperm begin swimming around in the spermathecae. There must be one or more signals that activate this movement and our findings suggest that odorant receptors may be the sensor that receives these signals."
The team made the finding when they noticed male mosquitos had an unusually high level of odorant receptors in their bodies; they were able to pinpoint the receptors in the males' testes. Past studies have also reported evidence of olfactory receptors in human sperm.
"Evidence for the presence of these receptors in human sperm is very solid. What is controversial is whether they play any role in human reproduction," Pitts said.
Researchers have since identified the chemical compounds that activate these odorant receptors and ones that prevented their activation.
The team found that when the mosquito sperm were exposed to odorant receptor activators and chemical compounds (some of which can be found in fennel) the tails started beating much faster; this did not occur if they were exposed to an agent that blocks odorant receptors. This phenomenon did not occur in mosquitos that were genetically altered to lack functional odorant receptors.
"This provides compelling evidence that the odorant receptors are involved in the reproduction process," Zwiebel said. "We know there is a lot more going on. We have just scratched the surface."
The findings could be used in insect control; researchers could use the information to work out a way to sterilize males mosquitos.