Promiscuity and vaginal bacterial diversity

By Razib Khan | December 17, 2011 10:10 am

It’s a fun fact that there are an order of magnitude more bacterial cells in your body than your own cells. Not only that, it’s well known that we wouldn’t flourish, let alone survive, without our gut “flora,” which digest material which would otherwise pass through out system. Not only are microbes good for us, but they’re also bad for us. The evolutionary flexibility of microbial pathogens is one of the major arguments for why sex exists among multiceullar species: it allows them to adapt to rapidly fluctuating disease pressures. Therefore, obviously the ecology of multicellular organisms’ microbial flora is essential to properly characterize. One element of the project involves genomics. This is not so easy for microbes because we don’t have the reference sequences of most of these organisms. We rely mostly on species which are easy to culture, and that does not include most lineages in the wild. That being said, there are workarounds, such as looking at the 16S rNA sequence, which is strongly constrained in bacterial lineages (i.e., it can serve as a “clock” to measure divergence of very deeply separated lineages).

With that, a new paper, Promiscuity in mice is associated with increased vaginal bacterial diversity:

Differences in the number of sexual partners (i.e., mating system) have the potential to exert a strong influence on the bacterial communities present in reproductive structures like the vagina. Because this structure serves as a conduit for gametes, bacteria present there may have a pronounced, direct effect on host reproductive success. As a first step towards the identification of the relationship between sexual behavior and potentially pathogenic bacterial communities inhabiting vital reproductive structures, as well as their potential effects on fitness, I sought to quantify differences in bacterial diversity in a promiscuous and monogamous mammal species. To accomplish this, I used two sympatric species ofPeromyscus rodents—Peromyscus californicus and Peromyscus maniculatus that differ with regard to the number of sexual partners per individual to test the hypothesis that bacterial diversity should be greater in the promiscuous P. maniculatus relative to the monogamous P. californicus. As predicted, phylogenetically controlled and operational taxonomic unit-based indices of bacterial diversity indicated that diversity is greater in the promiscuous species. These results provide important new insights into the effects of mating system on bacterial diversity in free-living vertebrates, and may suggest a potential cost of promiscuity.

These two species are sympatric and exhibit very different behaviors. Sympatric means that they aren’t geographically separated, so they are subject to the same environmental conditions. Rather, their distinctions on the species level seem to be due to behavior, in this case, the number of sexual partners of females. This then is a nice test for assessing the relationship of microbial diversity in the vagina as a function of partners. I suspect a priori you’d expect a positive relationship. And that’s what the author found. He presented a diversity index, but the results are rather intelligible visually. You can see clearly that the promiscuous species is characterized by a greater range of species richness than the monogamous one.

There are some studies of metagenomics of bacterial communities in humans. But to my knowledge it doesn’t look like there are any which have attempted to correlate number of sexual partners to diversity of vaginal flora. This is possible very important as a long term issue. The evolutionary biologist Paul Ewald has been reporting that there is a connection between history of infection and many late in life diseases, such as cancers. Mike Snyder had Stanford has been tracking his own biomarkers in extensive detail for several years, and has indicated that his own onset of Type II Diabetes was probably triggered by an earlier infection. These inferences were only possible because of his extremely rich personal data set, part of a broader project in his laboratory. But, it might give us a window into the more precise individual etiologies of diseases.

Citation: Naturwissenschaften. 2011 Nov;98(11):951-60. Epub 2011 Oct 1

Image Credit: Wikipedia, Wikipedia.

CATEGORIZED UNDER: Anthroplogy, Genomics, Medicine

Comments (10)

  1. zach

    Actually, just looking at those bar graphs it’s difficult to estimate/visualize diversity due to the impact of closure (normalizing to # of total sequence reads, results in population summations to 1). This makes it difficult to compare microbiota between groups, because the population levels are relative to other microbes in the individual. You need a distance metric that takes into account the compositional nature of this data. Unfortunately, shannon-diversity index is not robust to scale invariance, and so may not be appropriate in this case:

    Expect this issue to come up in the microbiome literature really soon. Full disclosure – this is what my current research is on.

  2. dave chamberlin

    It is getting unrealistic to demand that our brides be virgins but maybe we can demand low diversity in their vaginal flora.

  3. Great. Yet another ‘lifestyle choice’ we can throw at type II diabetes sufferers to make them feel bad.

  4. Justin Giancola

    best lead-in of the year.

  5. Yatima

    Whatever you think of Paris Hilton, using her picture to illustrate “promiscuity” is sexist.

    (And just to get it out of the way: why do some people say that feminists are humorless? Because we don’t laugh at things that aren’t funny.)

  6. Dan

    I’m surprised this has not gotten more attention – or perhaps I may be making it a bigger deal than it is – or, maybe what I’m about to say is too “traditional” and out of the times to be accepted by a progressive society but here goes…

    Is it just me or does this offer POTENTIAL (key word) of providing evolutionary reasons for why sex with multiple partners is bad? not what we’re meant for? – don’t really have a good term for what I’m looking for but so be it.

    While the findings of this paper aren’t that shocking (more flora diversity in vaginas of multiple partners), the implications may be. As Razib suggested in his conclusion, there is evidence that suggests that these bacterial communities in a mother may have long-term effects on their children…this again, to me at least, is not at all surprising. I assume we’ll find more evidence for this soon. Then, reading this brought me to thinking about BV ( Call me naive but… people of course have their social and emotional arguments for not having multiple sex partners (increased divorce rates, messes with emotional bonding, trivializes the act, etc.) but of course as you are probably going through your head now – these things can and often are disputed.

    Is this type of research, however, providing “scientific” arguments for this lifestyle choice that the sexual revolution of the 70s has basically made out to be a primitive lifestyle? Women, and men also, have been taught to embrace their sexuality, focus on getting what you want now, not being restricted to one man etc. etc. blah blah blah… so while people argue that this type of social / sexual revolution has led to drastic costs for society is it far off to say that they may also be contributing to health costs as well?

    BV has potential complications for pregnancy (pre-term birth, miscarriage due to PID, increased possibility of ectopic pregnancies, etc.) BV also drastically increases a woman’s susceptibility to HIV and other STI’s. Plenty of lit links BV to multiple sex partners. I just did a quick google search of ectopic pregnancy rates. The best I found is here: “In 1970, the Centers for Disease Control and Prevention (CDC) began to record the statistics regarding ectopic pregnancy, reporting 17,800 cases. By 1992, the number of ectopic pregnancies had increased to 108,800.”

    Two things to note – 1. the sexual revolution started in the 70s with the coming of Playboy and 2. Clearly the data did START in 1970 and I know this proves nothing but as I stated…this is just me throwing out hypotheses. Could it be that increased societal acceptance of multiple sex partners has led to an increase of BV (this part is factual of course) and thereby an increase in pregnancy problems AND FURTHERMORE, as Razib suggests, we may find out later on that these increases in flora in the reproductive systems of promiscuous women have affected the health of their children.

    All of this is very disturbing and sobering to me – perhaps I’m way off but I really don’t see it as that implausible. I’ll probably get owned since this may anger anyone that reads this since I’ll assume most people reading this are progressively leaning but so be it. We cannot have our cake and eat it too – much of what progressives have based their views on have been what evolution has told us and what nature has told us in response to our actions.

    I think there is some fantastic interdisciplinary research that can come from this type of study. No idea how Razib found this article in “Naturwissenschaften” but thanks for the post.

  7. Excellent points Dan, you’re right, I have NO idea why this didn’t get more attention! 😉 One small note, BV is typically characterized by a monoculture, or at least a reduction in diversity, so that specific example may be off, but the idea of direct fitness costs of promiscuity, ASIDE, from whatever effects on health, is good.

  8. AG

    Types or diveristy of HPV infection at cervix is related to the promiscuity and age starting sex.

  9. Aaron

    Greater bacterial diversity does not necessarily correspond with increased pathology. This is simply recording that the ecology in the promiscuous mouse vagina is richer than that of the monogamous. It behooves those of a scientific mind not to inject their own moral bias on the data. For all we know, further studies could show that this increased diversity actually provides a positive benefit to the host. Afterall, the immune system is, generally, a robust and adaptive one, and is best when kept primed. Such may be the case in the promiscuous mouse. Even if this does not bear true, it may be completely different for humans and other species. Do not think to create a fiction out of simple data points. Indeed, as the first comment notes, the graph given is a poor indicator of actual diversity and further tests should be conducted.

  10. Chris the Canadian

    Dan I can see your point on the bacterial/viral level, but certain aspects of the mammalian sexual anatomy tend to go against the theory that humans shouldn’t be promiscuous and should seek a life long partnership in mating. The male penis is shaped in a manner that is BECAUSE mammals are promiscuous. The head of the penis has that shape because if a female copulates with numerous partners, the male member can withdraw some of the existing sperm inside the vaginal track to give his sperm a chance to ultimately fertilize the egg. Also looking at male sperm, there are a wide array of types. Not all sperm are meant to fertilize the female egg. Some sperm set out to build walls to protect their bretheren on the road to fertility. Other sperm act as missiles, seeking out foreign bodies, including other mens sperm, to destroy them or entangle them and thus stopping their progress towards the egg.

    The ability for human and primate females to become pregnant (Not wait for a particular time of year to go into heat) is another adaptation higher mammals have to allow for more frequent opportunities to successfully fertilize, which in turn allows a female to have multiple partners to copulate with and fall pregnant with.

    With response to Yatima, you are complaining that Paris Hilton is used as an example of promiscuity? Really? Is there a more recognized and well documented person who could be a poster child for promiscuity? You have no sense of humor and your complaint that the picture is sexist tells me you are a bit uptight. Not everything is pre-meditated and just because a female picture was used doesn’t mean the original poster is sexist. If anything, Paris Hilton is the PERFECT example of promiscuity.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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