Olfaction and Nocturnal Sex Drive in Drosophila

The 11th annual CNR Rao oration award lecture was given at JNCASR this past Monday, by a chronobiologist, Dr. Vijay Sharma, from the EOBU, JNCASR. Before I try and explain what his talk was about, here are a few general notes: a) Chronobiology is for adults. b) The general populace at JNCASR in general isn’t as adult as I would like, with the odd giggle when ‘Sex’ is put up on the title of some slide c) But it also isn’t as bad as I might fear; the giggles were few and most people listened stoically to the talk on sexual drive in Drosophila.

Chronobiologists study biological processes that occur in cycles or rhythms. Everything from the sleep-wake cycle in human beings to how often Drosophila want to mate fall under the purview of chronobiology. Most of these cycles, especially those that are possibly important for human beings, are circadian (meaning circa = roughly diem = daily). Drosophila, of course, is studied because it is so ravenously libidinous (read horny), and produces new generations very quickly. The talk was about if, and how, the olfactory system in Drosophila affects its nocturnal sex drive.

The speaker started by explaining that Drosophila are observed to have markedly reduced sleep-time when a male and a female are put in proximity. (After saying this, the speaker talked about how he had severely edited his presentation for the PG audience present, and how there was a Director’s cut that could be obtained on request.) It was also mentioned that there is no reduction in nil-activity time when two members of the same sex are put in proximity. (“See? Homosexuality isn’t ‘Natural’!”) We infer from this (and the singing and dancing and wooing that are part of Drosophila courtship) that the Drosophila must be at it whenever there’s a flurry of activity in a certain cell but the control group is sound asleep.

This leads to the question of whether there are factors that can disrupt this nocturnal sex drive. Does the animal communicate through visual cues? (There are dances that the males perform as part of the courtship rituals) Does hearing play a role? (the males also ‘sing’, apparently; so yes.) Or, the question that was considered here, does the olfactory system play a role?

They answered this by a combination of physically or hormonally destroying various targeted regions in the sensory cortex of the insect (we can point to a bunch of neurons and say if they are involved in the olfactory or the visual or hearing systems; the science is that good), and seeing if there’s any difference in the night-time behaviour.

I can’t really claim to have understood the techniques that were described for ablation of olfactory neurons. The long and short of it is that the olfactory system seems to play a role in the nocturnal sex drive. There is also evidence to suggest that the olfactory system’s role is sexually asymmetric. Male Drosophila that have their noses cut off (PS: figuratively) are much more debilitated in their libido than their female counterparts.

That’s a little counter-intuitive, if you think about it. The male does the dancing, singing, and wooing. Presumably, then, the male also releases some sort of pheromone. By this logic, a damaged olfactory system in the female should be worse for the sex drive. This line of reasoning is borne out by the finding that a damaged olfactory system disrupts the sex drive, even if it is only damaged after courtship is complete; i.e, it is actually essential for copulation. It might be interesting to find out why this is so.

[Imagine that. The nose is essential for copulation. It’s as if the male can’t find… never mind!]

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Update: I’ve changed my mind about JNCASR being an adult place. As you can notice, the url for this page has the word ‘sex’ in it, and I can’t visit this url from inside JNCASR. For crying out loud!

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