Female fruit flies are notoriously promiscuous insects that respond to the courtship song of a male by activating their immune system. Why? The accepted explanation is that they anticipate mating and, at the same time, they anticipate the possibility of contracting sexually transmitted diseases – therefore, they get ready to defend themselves from the attack of infectious microbes using the so-called immune anticipation of mating.
Now, results from a study carried out at the University of Bath in the UK and published in the journal Proceedings of the Royal Society B: Biological Sciences (October 30, 2013) show that immune anticipation is indeed a protective mechanism against sexually transmitted diseases in female fruit flies. The study, titled “Immune anticipation of mating in Drosophila: Turandot M promotes immunity against sexually transmitted fungal infections“ focuses on a fungus (Metarhizium robertsii) and identifies Turandot M as a major player in the mechanisms that provide protection against sexually transmitted Metarhizium infections.
Turandot M, a member of the Turandot family of immune and stress response genes, is up-regulated in response to courtship and in anticipation of mating. The study suggests that up-regulation of Turandot M might be a general mechanism at the basis of immune anticipation in insects, underlining the intimate link between brain, behavior and immunity.
As the researchers state in their paper “mating is fraught with danger” – fortunately, female fruit flies know how to defend themselves.
Copyright © 2014 Immunity Tales.
Wow, that is a cool defense mechanisms. This is probably a fine example of evolution at work here. Most likely the population of fruit flies at one point in their lineage was being afflicted by STDs such as the fungus Metarhizium robertsii. Because of this only the female fruit flies in the population who regularly used immune anticipation were able to survive while those who did not were infected and subsequently died, thus creating a population of fruit flies were immune anticipation is the norm. The article only mentions female fruit flies carrying out this act and not the males which is probably related to their promiscuous activity. Do the male fruit flies not have as many mates throughout their lifetime? Are the male fruit flies even capable of up-regulating Turandot M? Also I am curious to know if humans have any mechanism that potentially mimics or resembles the up-regulation of Turandot M.
I don’t think we discover something similar to Turandot M in human so far. That would be awesome if we have this kind of protection from STDs. However, regarding immune response during intercourse, some women with a specific HLA can actually produce something called sperm-immobilizing antibodies in their sera. Unfortunately, these antibodies lead to infertility in many women by preventing sperm passage and normal fertilization process. I think in this case, the immune system treats the sperm as a harmful factor. The chemical substances of a sperm might cause allergic reaction inside the women’s bodies. The HLA from these women might bind to molecules present on the sperm, thus activates CD4 T cell and eventually plasma cell. This mechanism is obviously not as beneficial as Turandot M but it shows that the female immune systems of many species have a way to get rid of disadvantageous factors during courtship or fertilization. The protection is not necessarily to fight against STDs but anything that is harmful.
It’s interesting that female fruit flies use immune anticipation to defend against possibly contracting sexually transmitted diseases, but how exactly do these Turandot M genes get up-regulated in response to courtship? Once the female fly hears the courtship song from the male, how does that translate to her actively modulating the genes needed for immune anticipation? I’m really curious as to how simple sound waves can result in such a immune response. Frankly, I could see how immune anticipation can be activated if the males released pheromones during courtship that then trigger the female’s immune system in preparation for copulation. It’s an actual chemical message that’s secreted to elicit a response. Many species of insects use pheromones to attract mates and to alter the receiving mate’s social or sexual behavior. Since that’s not case in fruit flies, I hope there will be more studies on how courtship songs can activate immune anticipation in female fruit flies prior to mating.
I would assume that the immune system is activated just by hearing the song prior to mating because it’s considered part of the “foreplay” that occurs. The female fruit fly’s body begins to prepare itself for mating and in doing so, it activates its immune anticipation so it can protect itself against sexually transmitted diseases. I wouldn’t say that the sound waves themselves elicit the immune anticipation. Rather, the immune anticipation might be coupled with preparing to accept sperm from the male fruit fly.
The findings from the study by researchers at the University of Bath give insight on how the immunity of Drosophila can reduce fitness costs associated with reproduction. Sexually transmitted infections are a problem faced by many species on Earth during reproduction. For humans, one of the most prominent STIs is HIV/AIDS, which affects millions of people around the world. A big question that is sparked by studies like this is whether humans can develop a way to stimulate the immune system to recognize and defend against pathogens before infection. This would be a great defense against HIV, which infects helper T cells, a significant part of the adaptive immune system.
Obviously, this is a huge leap for researchers. However, this study gives foundation for solving significant problems caused by pathogens. Although Drosophila may be a very different species from humans, they can give us insight on how our immune system functions. A possible step researchers can take is to study a mammalian model organism for genes homologous to Turandot M. Through these studies, we discover fundamental concepts of immunity that could eventually pave way for finding cures or vaccinations to various human diseases.
HIV/AIDS is what first came to mind for me as well. It is primarily transmitted through sexual intercourse, and given the relatively immediate and deadly nature of the disease if untreated it poses the greatest selective pressure on the human species compared to other STDs. Obviously it would take too long to for a natural response to develop during the course of our lifetimes, but that doesn’t mean we couldn’t find a way to induce such a response. Further study of HIV/AIDS patients could lead to the detection of some external signaling factor. Who knows maybe we could train some dogs to sniff out those infected with HIV, then we could isolate that signal. And if we can do as you suggest and study homologous genes in humans to up-regulate the immune response. Then all we would have to do is create a drug that would facilitate response to that signal and we would be able to prevent further spread of HIV/AIDS. This is clearly a long shot, and a rather indirect way of solving the problem, but the to find the best solution to a problem we have to have different solutions to chose from.
I didn’t know fruit flies were susceptible to STD’s, for some reason I find this is kind of amusing. Like tbrown110 said this has to be some type of evolution in fruit flies, however this is very advantageous for them. If this evolution occurred in humans this would reduce transmission significantly. If it is solely the promiscuity of female fruit flies that makes them impervious to STD’s then would promiscuous males also be impervious to STD’s or has this discovered. Are humans at risk for contracting an STD from a fruit fly like mosquitoes can give humans west nile virus?
That’s an interesting question and in my opinion, I would think that humans wouldn’t be able to contract STDs from fruit flies just for the fact that Sexually transmitted diseases are passed on through fluids, skin-to-skin contact and blood. It’s known that fruit flies don’t “bite” people, so there’s no possibility of them passing on STDs from one person to another. Also diseases like HIV can’t even live outside of a human’s body, therefore it would be impossible to transmit it through a fruit fly because they aren’t known to reproduce in them. I have heard of instances where bestiality can cause STDs in humans because of sexual contact with animals, but never of insects like a fruit fly passing on something like that.
Turandot is a family of genes in several Drosophila species that are expressed during stressful conditions including bacterial infection, high temperatures, and exposure to UV light (1). (Sidenote: Interestingly enough, Turandot is also the name of an Italian opera set in China (2). Turandot is a princess who remembers the loss of an ancestor to a prince and therefore is cold towards and refuses to marry any prince that seeks her hand in marriage. There are parallels to the story and a female fruit fly protecting herself from the dangers of stressful situations including mating.)
The methods section of the study mentioned above described the use of genetically engineered strains of male fruit flies that expressed some of the Turandot proteins (3). From this, it seems male fruit flies are at least capable of expressing Turandot genes, but I am not entirely sure if they naturally have these genes to begin with. What would be interesting to know is how the immune system becomes activated. Before reading this article, I only knew of the immune system activating in the presence of antigen. This study indicates that up-regulation of Turandot M helps activate the immune system and yet another study conducted on sex peptides in fruit fly seminal fluid elicits the synthesis of antimicrobials in the female reproductive tract (4). This lead me to believe that TotM is just one of many players involved in this response.
Flies in general are promiscuous. They engage in multiple copulations to maximize the amount of eggs that are fertilized. This results in competition. In an evolution class, I learned of other species of flies that in which the males literally scoop out the sperm left inside the female from a previous copulation. Flies have to compete not only with other organisms within their species, but diseases that can be sexually transmitted. Hence, female fruit flies utilize immune anticipation as a mechanism to defend itself from the sexually transmitted diseases. Evolution has favored the up regulation of Turandot M to protect against Metarhizium fungal infection. I am curious to know what effect the Turandot M up regulation has had on Metarhizium. Has Metarhizium evolved to evade the up regulation of Turnandot M?
Wow, I had no idea that fruit flies can contract STDs. The female being able to combat diseases from the male is pretty amazing, now if only humans can have a mechanism like this. When reading the article, I kept wondering why males were so diseased, so I did a little research. Males have toxic proteins in their sperm fluid that are actually harmful to the female fly. An article describes the male as almost a sickness to the female, that’s why they have an immune response when mating. This then leads to the question, what good is it to have this toxic sperm? Well, the article also states that if males didn’t make the females “sick” then there would be a 20% increase in the number of offspring. I believe that this illness between the male and female is like a population control. Since males are so toxic to females, the number of offspring is decreased which results in more food for the overall population and female flies that have better immunity towards the male toxins.
I, too, was unaware that fruit flies were susceptible to STDs. As narrow minded as it sounds, I have never really thought of any other species contacting STDs. I find it so fascinating that the female fruit fly is able to prepare and anticipate internally the possibility of contracting such diseases and is able to send an immune response as a preventative measure. But, is it evolutionary? It seems like a survival of the fittest characteristic that has molded and formed into the strategy it is used for, today, but how much is really known? Why is it just females that utilize this preventative tactic? Regardless, I find it extremely interesting, and the Foundation for Bio-medical Research said it best: “So it seems that at least in flies, the sweet sound of a lover’s voice may actually be good for one’s health.”