History has been witness to as many stories of jealousy, as that of love. They are actually two sides of the same coin. I knew this from both my personal experiences as well as from the little knowledge of human history I had. When I started studying natural science, I never knew that I was up for more about the same theme. But very soon I realised, even natural history is studded with numerous stories of jealousy. One curious thing about them is, jealous males, for some reason, are more talked about than jealous females. I learned about creatures which guard their wives like treasures, some even use chastity belts (biologists like to call them – “mating plugs”). Fight among rival males for access to the priced maid is so common that great Charles Darwin had to write one full book talking about them. However, after Darwin, it was a slow progression of events that saw the relationship between males and females scrutinized and re-scrutinized. And still the debate is not over. As a young undergrad student I was always fascinated by this debate and the inspiration led me to take up this study as full time occupation for few years during my doctoral research. I started watching little flies in their artificial homes. I wondered what kind of information I might gain by watching them, as they seemed to me useless little flies always preoccupied with feeding. However, one curious thing caught my eyes. The males of these tiny insects seemed to be never out of their sexual lust and not much into feeding business. So much so that I felt pity for the females, how do they tolerate this coercion? On the other hand, how do the males cope with their almost continuous activity of courting the females? More surprising it appeared to me, as my teacher once told me that mating seems to be costly to females (which is understandable) but not so for males and that is why they can go around mixing and mating with several females at will! The paradox to me was, if males spend so much of their energy just dancing, singing and chasing other males and still end up spending almost no time eating, then how can the whole activity be costless?
The beauty of the flies I was looking at was it not only let me ask questions but also gave me a way to perform scientific experiment to solve them. Keeping all these questions in mind I set off for my first scientific study. I started studying the males. Soon I figured out (from others’ work) that males not only dance and sing but also pass on some \“tokens of love\” to their maids while making love. And as it turned out these tokens are symbols of jealousy and equivalent to the chastity belts in other organisms. I wondered whether love making becomes longer if males are more jealous, just to ensure that his maid is sufficiently flooded with his gametes and the tokens. To test my suspicion I started observing their love making processes under different conditions. After spending a long time observing them and with the help of a gang of very keen, young observers, I realised that something similar to my suspicion happens with these flies. At the end of my observation I figured out that males indeed become jealous by seeing other males around. Under their natural condition they see around 15 more rivals around and they mate for 19 minutes on an average (quite an achievement that would make even the most proud human feel ashamed of their own performance). And given that the actual process of impregnation takes only few minutes, jealousy seems to be reason of this long love making process. Now, for a lonely male, where there is no real cause of immediate jealousy, this duration came down by about 36 percent – a confirmation of the jealousy hypothesis. However, there was an even bigger surprise! When there are more number of rivals than usual (about twice), males seemed to become over jealous and loose all hope and thereby reduce the duration of their priced behaviour by 10.5 percent. Well, Darwin would have asked, so what – do all these manipulation by males affect their efficiency of fathering young ones (Darwinian fitness)? After all, that is what matters to evolution and to recall Sir Peter Brian Medawar’s saying: “For a biologist, the alternative to thinking in evolutionary terms is not to think at all”. As it turned out this behavioural manipulation had a strong correlation to their Darwinian fitness. Males that spent too little time (out of either over confidence or over jealousy) wooing his maid ended up siring less number of offspring compared to males that spent quality time doing the same. In other words, (for fruit flies) time spent doing the most talked about thing turned out to be a very good predictor of a male’s success in sexual rivalry – something that might bother most of my male colleagues. So not only humans but also the males of even these tiny fruit flies care about the intensity of sexual rivalry and assess it by some social cues associated with the number of rivals. Their assessment leads to some modification of their investment per maid, a behaviour which is closely connected to their efficiency of fathering young ones.
It not only let me and my male colleagues learn an important lesson of “life”, but also gave us a strong reason to believe our starting hypothesis. No longer, we could look at males as mere gamete producing machines, copulating with whatever they can get their hands on.
As is the case most often in science, getting an answer to a question only paves the way for more questions about the same phenomena: our new understanding of the male reproductive behaviour only made us ask several other exciting questions which have been ignored so far. Do males choose between available females in some obscure way? If jealousy and love are inseparable, then if perception of jealousy is altered – say, when engaging in adultery (either be the cuckolded male or the cuckolder), when there are lot of handsome rivals around, do males respond to the altered change? More interestingly, if some population experience more or less jealousy, do they evolve to cope with that? If they do what evolutionary novelties enable them to do that and how far they are connected to other physiologies of the organisms? Our small study showed that even such a simple aspect of an organism’s behaviour as how long to mate is under strong selection pressure. Thus one can only imagine the complicated mechanism of evolution of reproductive behaviour and physiology of organisms. I wonder whether we are even half way through with the most superficial understanding of the most fundamental aspect of our life.