Evolution on the fly: Look, Ma! No genes!

U. ROCHESTER (US)—Researchers have identified a new mechanism for evolution that bypasses genes altogether.

A research team has chronicled a striking example of a bacteria infecting an animal, giving the animal a reproductive advantage, and being passed from mother to children.

This symbiotic relationship between host animal and bacteria gives the host animal a readymade defense against a hazard in its environment and thus has spread through the population by natural selection—the way a favorable gene would. Details are reported in the journal Science.

The work by University of Rochester biologist John Jaenike and colleagues provides the first substantial report of this effect in the wild, but he says it may be a common phenomenon that has been happening undetected in many different organisms for ages.

Aside from shedding light on an important evolutionary mechanism, his findings could aid in developing methods that use defensive bacteria to stave off diseases in humans.

Jaenike studies a species of fly, Drosophila neotestacea, which is rendered sterile by a parasitic worm called a nematode, one of the most abundant, diverse, and destructive parasites of plants and animals in the world.

Nematodes invade female flies when they are young by burrowing through their skin and prevent them from producing eggs once they mature. However, when a female fly is also infected with a bacteria species called Spiroplasma, the nematodes grow poorly and no longer sterilize the flies, Jaenike found.

He also discovered that, as a result of the Spiroplasma’s beneficial impact, the bacteria have been spreading across North America and rapidly increasing in frequency in flies as they are passed from mother to offspring. Testing preserved flies from the early 1980s, Jaenike found that the helpful bacteria were present in only about 10 percent of flies in the eastern United States. By 2008, the frequency of Spiroplasma infection had jumped to about 80 percent.

“These flies were really getting clobbered by nematodes in the 1980s, and it’s just remarkable to see how much better they are doing today. The spread of Spiroplasma makes me wonder how much rapid evolutionary action is going on beneath the surface of everything we see out there,” Jaenike says.

He reasoned that the substantial increase in Spiroplasma infection was an evolutionary response to the recent colonization of North America by nematodes. As the nematodes invaded the continent, the bacteria proved to be a convenient and potent defense against the nematodes’ sterilizing effect.

Now, the majority of flies in eastern North America carry the bacteria, and the bacterial infection appears to be spreading west. Without any mutation in their own genes, the flies have rapidly developed a defense against an extremely harmful parasite simply by co-opting another organism and passing it on from generation to generation.

“This is a beautiful case showing that the main reason these Spiroplasma are present in these flies is for their defensive role,” says Nancy Moran, the Fleming Professor of Ecology and Evolutionary Biology at Yale University. Moran studies the role of defensive symbionts in aphids. “These heritable symbionts are a way for an animal host to acquire a new defense very quickly. One way to get a truly novel defense is to get a whole organism rather than mutating your own genes that aren’t that diverse to begin with.”

Jaenike’s work could also have implications for disease control. Nematodes carry and transmit severe human diseases, including river blindness and elephantiasis. By uncovering the first evidence of a natural, bacterial defense against nematodes, Jaenike’s work could pave the way for novel methods of nematode control. He plans to investigate that prospect further.

Researchers from the University of Victoria in British Columbia contributed to the work, which was funded by the National Science Foundation.

More news from the University of Rochester: www.rochester.edu/news/

chat28 Comments


  1. enirdlinger

    A really interesting concept! It reminds me of the theory that our mitochondria were once separate organisims, which developed a symbiotic relationship with other primative live forms and then eventually evolved into the mitochondria we all posess in our bodies!

  2. Aaron

    It certainly reinforces that engulfing theory, as opposed to membrane in-folding. I’m a little confused about some of the word usage in these lines:

    “He reasoned that the substantial increase in Spiroplasma infection was an [evolutionary response] to the recent colonization of North America by nematodes”-

    As if it were some kind of conscious reaction to a perceived threat, as opposed to a mere coincidence with a positive reaction which through reproductive success increased its frequency. I believe that is also being said here, but I still get the impression that the notion of intention is implied. Is this a common belief among evolutionary biologists?! Or have I just misinterpreted what is being said here.

    The notion of intention is repeated in this line:
    “This is a beautiful case showing that [the main reason] these Spiroplasma are present in these flies is for [their defensive role],”

    Clearly a benefit for the fly, but what is the motivation of the Spiroplasma? That would be what I’d consider the main reason for their being there.

  3. Roy Niles

    Instead of the notion of intention, the more apt metaphor to use would be the notion of purpose.

  4. Aaron

    No, I meant specifically what I said. Although I can see why you’d say that, I’m not denying purpose. A thing can serve a purpose unintentionally. Like I said, I may have the wrong idea entirely about what i considered could have been implied. It would be my guess that the spiroplasma didn’t infect the fly under the impression that it was serving some beneficial purpose for the fly, if it had any impression of what it was doing at all.

  5. Roy Niles

    The unintended consequence of purpose can look a lot like consequence consistent with intention.
    We must assume the primary motivation of Spiroplasma to be in service of its own purposes.

  6. Aaron

    Precisely! That would be my understanding as well. Which is why I was confused by one of the above statements in the article.

  7. David

    Aaron –
    “Evolutionary response” refers to the forces that affect the flies and the frequency of Spiroplasma-fly coexistence. The Spiroplasma infected the flies because it is a parasite, which had the unintended consequence of making the fly a poor Nematode host, which in turn allowed that fly to reproduce, and have offspring that were infected by Spiroplasma (I would imagine during the pregnancy). Thus, the fly-Spiroplasma symbiosis becomes established by Natural Selection, which is the Evolutionary Response to this scenario (an environment with flies, Spiroplasma and Nematodes).

    There is NO intention or purpose. The evolution of Spiroplasma-fly symbiosis is something that is selected for due to the induced forces in the system by the Nematodes.

  8. Roy Niles

    “Unintended consequences” at the very least would serve the purposes of natural selection in this scenario, whether you follow the outdated neo-Drwinistic view of blind selective forces at work or not. Otherwise the concept of consequence does not apply.

  9. Roy Niles

    But in any case we now understand that all biological entities have decision making capabilities, the use of which is continuous and purposive.

  10. Aaron

    Thanks David for the explination. I understand the nature of their symbiotic relationship, and how evolution is understood to work. I find some of the terminology misleading. My complication with some of the phrasing appears to be purely a matter of definition.

  11. Walter

    Does water intend to fall?
    No more than the spiroplasma intends to make the fly a poor nematode host.

  12. Roy Niles

    Another dumb “water doesn’t think to run downhill” analogy to confirm a bias against intelligence and purpose as biological strategies.

    Get an education. Start here: ftp://ftp.eeng.dcu.ie/pub/alife/bmcm9401/varela.pdf
    Autopoiesis and a Biology of Intentionality

  13. JTK

    I don’t think you should be telling people to get an education, Roy. You obviously aren’t talking about well accepted scientific principles, you are talking about fringe science/pseudoscience. Can you name an evolution course that would teach the principles you mention? If not, it might be a sign that you are the one that needs some schooling.

  14. Roy Niles

    JTK: It’s not a scientific principle that water runs down hill because it made a plan and chose to. (Or will you confirm you think it is?) But it is accepted by evolutionary biologists (who do teach courses on occasion) that spiroplasma and their kin not only run downhill by plan and choice, but over the river and through the trees as well. Life forms plan to explore, and choose to learn. Water doesn’t. Read the cited paper if you can understand it. That’s the education I made reference to.

  15. JTK

    Your mumbo jumbo doesn’t impress me. You are spouting a fringe theory and don’t have the guts to admit that it isn’t taught in evolutionary biology classes. If it was remotely credible you would be citing countless people who agree with it, instead you are verbally masturbating.

  16. Roy Niles
  17. enirdlinger

    Roy, like many bores, has hijacked the conversation on a really interesting article. Can we ignore him and redirect the discussion in a way interesting to a larger group of people?

  18. Roy Niles

    If you can, why don’t you?

  19. JTK

    Bugger off, woo-troll.

  20. Roy Niles

    How wonderfully bright and interesting of you. Care to tell us what you learned that makes you smarter than Francisco Varela?

  21. wjv

    So are these researchers are claiming this is the first instance of evolution via a mechanism that isn’t caused by genetic mutation? Because I can think of many examples of evolution in humans not caused by genetic mutations… they all involve technology.

    Think about it: if obtaining a bacterial symbiont equates to selective force, then it’s analogous to say that knowledge of agriculture was selective, so would be powered transportation, computing etc. Vast majorities of our human population are “colonized” by these technologies so can these researchers look at that phenomenon the same way?

  22. enirdlinger

    WJV’s comment concerns social evolution and is an interesting concept. The difference between that and what is discussed in this article is that a material change occurred within the individual’s body and is now transmitted through sexual reproduction. I think that current thinking is that our miochondria evolved in a similar manner from a symbiotic relationship between two organisms (our DNA comes through our mother) , but can think of no other similar inheritance.

  23. David

    Aaron – You’re quite welcome. I didn’t mean to be condescending, and I certainly hope I wasn’t.

    Social evolution is quite an interesting phenomenon. Until recently, biologists believed that culture had actually stopped human evolution, and so we’d be stuck in a Homo Sapiens state until the end of, well, at the very least, the end of all culture.

    However, the newest research (and if you think about it a little bit, I think you might agree) suggests that culture has exactly the opposite effect: It accelerates evolutionary change.

    On the other hand, I do agree with enirdlinger: I think this concerns more the physical inheritance of Spiroplasma and the increase of fly-Spiroplasma symbiosis frequency than it does to evolution unrelated to genes. I have never heard of other examples though…. for some reason, I just don’t think of mitochondria —-> eukaryotic cells evolution path as the same, but that’s just me.

    And at the risk of kicking a dead horse:
    Roy, I thought the concept of an autopoeitic system was that it was a system (usually living) that has a network of operations and or processes that is able to respond, to some degree, to perturbations in the system. This STILL falls within the theory of Microevolutionary Theory, which is, as you will undoubtedly know, just the microscopic extention of Darwin’s theory of Evolution.

  24. Roy Niles

    Darwin’s theory allowed for the heritability of learned behaviors, but largely because of the Weismann Barrier hypothesis, the neo-Darwinians held that such experiences were not to be considered as effecting the selection process – hence the belief that the organism’s purposes could play no part in its evolution – with the further belief that organisms had no purposes of their own to begin with. This belief is now changing as it is recognized that organisms act.in anticipation of results, and learn from their mistakes in a trial and error fashion. These experiences, to the extent that they are successful, eventually become instinctive. And heritable.
    Instincts are purposeful, even though the organism won’t know their ultimate goal when acting as the instincts direct it to. There is a form of intentional choice involved here based on short term expectations – which if successful lead to further choices as the instinctive process directs. Not all parasites will attain the results their instincts ultimately were after. Those that do will be rewarded by their replication. Instincts will be enhanced by experiences over time as well. That’s the short version. These ideas are part of the curriculum in most universities, and much as been written on this by the modern evolutionary biologists, such as Shapiro, Margulis, Lamb, Jablonka, Adduter, Rose, Ayala, and numerous others – including Varela, as I first mentioned. That paper will explain autopoiesis much better than I can. This doesn’t invalidate microevolution, it just puts purpose back in the equation.

  25. Manu Ganji

    “Testing preserved flies from the early 1980s, Jaenike found that the helpful bacteria were present in only about 10 percent of flies in the eastern United States. By 2008, the frequency of Spiroplasma infection had jumped to about 80 percent.” <–what does that mean?

    Does it mean… they preserved these files all along from 1980s – 2010 in isolation and they found the proportion of bacteria infected flies to increase? Please help. Thanks in advance.

  26. david lloyd thomas

    I am more than confused that this example of co-existent benefit is considered an evolutionary change.

    1. The nematode was harming the fly’s reproduction.
    2. The bacteria’s introduction harmed the nematode’s reproduction.
    3. That second introduction allowed the fly to reproduce according to design.
    4. There is no evolution here.

    This “fly/nematode/bacteria” interaction is not even the same as the Fig Tree/ Fig Wasp relationship that has apparently existed as necessary for their interdependant existence.

    If a virus came along and interferred with the bacteria, then the nematode would be back at work making its home in the fly. The fly would be idential to the fly before bacteria versus after bacteria. That is, there would be no change in the fly. No evolution has taken place.

    In fact, this is not even an example of micro-evolution.

  27. Babu G. Ranganathan

    NATURAL LIMITS TO EVOLUTION: Only micro-evolution, or evolution within biological “kinds,” is genetically possible (such as the varieties of dogs, cats, horses, cows, etc.), but not macro-evolution, or evolution across biological “kinds,” (such as from sea sponge to human). All real evolution in nature is simply the expression, over time, of already existing genes or variations of already existing genes. For example, we have breeds of dogs today that we didn’t have a few hundred years ago. The genes for these breeds had always existed in the dog population but never had opportunity before to be expressed. Only limited evolution or adaptation, variations of already existing genes and traits, is possible.

    The genes (chemical instructions or code) must first exist or otherwise the evolution cannot occur. Genes instruct the body to build our tissues and organs. Nature is mindless and has no ability to design and program entirely new genes for entirely new traits. Nature can only work with the genetic ability already existing in species. Nature cannot perform the genetic engineering necessary to increase that genetic ability.

    Many people have wrong ideas of how evolution is supposed to work. Physical traits and characteristics are determined and passed on by genes – not by what happens to our body parts. For example, if a woman were to lose her finger this wouldn’t affect how many fingers her baby will have. Changing the color and texture of your hair will not affect the color and texture of your children’s hair. So, even if through physical exercise an ape’s muscles and bones changed so that it could walk upright it still would not be able to pass on this trait to its offspring. Only changes or mutations for traits that occur in the genetic code of reproductive cells (i.e. sperm and egg) can be passed on to offspring. Read the author’s popular Internet article, HOW DID MY DNA MAKE ME? Apes, by the way, are quite comfortable in how they walk, just as humans are quite comfortable in how they walk. Even a slight change in the position of a muscle or bone, for either, would be excruciatingly painful and would not be an advantage for survival.

    The new science of epigenetics shows that certain acquired traits from the environment that affect how genes are expressed may be passed on (i.e. whether a gene is turned on or off), but these certain acquired traits do not change or alter the fundamental structure or function of the genes themselves.

    Modern evolutionists believe and hope that over, supposedly, millions of years random genetic mutations in the genes of reproductive cells caused by environmental radiation will generate entirely new genes. This is total blind and irrational faith on the part of evolutionists. It’s much like believing that randomly changing the sequence of letters in a romance novel, over millions of years, will turn it into a book on astronomy! That’s the kind of blind faith macro-evolutionists have.

    When evolutionary scientists teach that random genetic mutations in species over, supposedly, millions of years caused by random environmental agents such as radiation, produced entirely new genes (i.e. genetic code or genetic information) leading to entirely new forms of life, they are not teaching science but simply a faith, a belief!

    What about natural selection? Natural selection doesn’t produce biological traits or variations. It can only “select” from biological variations that are possible and which have survival value. The term “natural selection” is a figure of speech. Nature doesn’t do any conscious selecting. If a variation occurs in a species (i.e. change in skin color) that helps the species survive then that survival is called being “selected.” That’s all it is. Natural selection is a passive process in nature, not a creative process.

    How could species have survived if their vital tissues, organs, reproductive systems, etc. were still evolving? A partially evolved trait or organ that is not complete and fully functioning from the start would be a liability to a species, not a survival asset. Plants and animals in the process of macro-evolution would be unfit for survival. For example, “if a leg of a reptile were to evolve (over supposedly millions of years) into a wing of a bird, it would become a bad leg long before it became a good wing” (Dr. Walt Brown, scientist and creationist). Survival of the fittest actually would have prevented evolution across biological kinds! Read my Internet article: WAR AMONG EVOLUTIONISTS! (2nd Edition).

    All species of plants and animals in the fossil record are found complete, fully-formed, and fully functional. This is powerful evidence that species did not come into existence gradually by any macro-evolutionary process but, rather, came into existence as complete and ready-to-go from the very beginning, which is possible only by special creation.

    All the fossils that have been used to support human evolution have been found to be either hoaxes, non-human, or human, but not non-human and human (i.e. Neanderthal Man was discovered later to be fully human). Textbooks and museums still continue to display examples and illustrations supporting human evolution which most evolutionists have rejected and no longer support. Many diagrams of ape-man creatures over the years were reconstructed according to evolutionary interpretations from disputable bones that have now been discredited but still being taught in school textbooks.

    What about genetic and biological similarities between species? Genetic information, like other forms of information, cannot happen by chance, so it is more logical to believe that genetic and biological similarities between all forms of life are due to a common Designer who designed similar functions for similar purposes. It doesn’t mean all forms of life are biologically related! Only within a true species can similarities be used as evidence for relationship because only within a true species can individuals be capable of mating and producing offspring.

    Also, so-called “Junk DNA” isn’t junk. Although these “non-coding” segments of DNA don’t code for proteins, they have recently been found to be vital in regulating gene expression (i.e. when, where, and how genes are expressed, so they’re not “junk”). Read my popular Internet article: HOW FORENSIC SCIENCE REFUTES ATHEISM

    The real issue is what biological variations are possible, not natural selection.

    Visit my latest Internet site: THE SCIENCE SUPPORTING CREATION .

    I discuss: Punctuated Equilibria, “Junk DNA,” genetics, mutations, natural selection, fossils, dinosaur “feathers,” the genetic and biological similarities between various species, etc., etc.

    Babu G. Ranganathan*
    (B.A. theology/biology)


    *I have had the privilege of being recognized in the 24th edition of Marquis “Who’s Who In The East” for my writings on religion and science. I have given successful lectures (with question and answer period afterward) before evolutionist science faculty and students at various colleges/universities.

  28. Paul

    Its amazing how far they have come with technology with advancement to the medical field. It just increases every year with the latest technology being developed.

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