Thursday, April 26, 2012

The Story Behind Our New Review: "Speciation by Symbiosis"

This post is a behind-the-scenes look at our new review, entitled Speciation by Symbiosis, by graduate student Robert Brucker and I. The review is online today in Trends in Ecology and Evolution. If anyone needs a copy, Ill happily send you one. Here are four points that motivated us to write the review.

1. The study of microbial symbionts in speciation has an interesting history: One of the central questions in evolutionary biology remains how do new species arise. What types of genes and evolutionary forces spur one species to split into two, ultimately to form the 1.8 million species on the planet? While we clearly have answers today that shed some light on these questions, debate remains about what types of heritable factors are important in promoting speciation. Specifically, these factors include two possibilities: (i) the genes on an organism's chromosomes versus (ii) the microbial symbionts that inhabit that same organism. The controversy over this topic actually began a century ago among evolutionary biologists and geneticists.  The main demarcation in the debate was best represented by two books, one of which was nearly forgotten to history and is the inspiration for the review, as well as our grant (press release) from the National Science Foundation's Dimensions of Biodiversity Program.

The forgotten book and the famous book that complements it are:
  • by microbiologist Ivan Wallin - Symbionticism and the Origin of Species (1927), and 
  • by geneticist Theodosius Dobzhansky - Genetics and the Origin of Species (1937)
Given the uncanny similarities in titles and the time frame of their publications, I think it is likely that Dobzhansky "copied"  Wallin's title and replaced Symbionticism (meaning intracellular symbioses with microorganisms) with the word Genetics.

A 1920 photo of Ivan E. Wallin. Wallin was a professor in the Department of Anatomy at the Univ. of Colorado Medical School, Boulder and was most well known for recognizing that mitochondria as bacteria. Credit: Archives, University of Colorado at Boulder Libraries. Colorado, U.o. (1920) Junior Class. In College of Liberal Arts, Univ of Colorado, Boulder.

2. Ivan Wallin's Hypothesis Was Ahead of His Time: Wallin’s central thesis was that the universality of bacterial-derived organelles (i.e., mitochondria) reflected the importance of bacterial symbionts as building blocks of evolutionary change and ultimately new species. Despite Wallin’s effort to put microbial symbiosis into the mainstream of evolutionary biology in the early 1900's, it was Dobzhansky’s work that would have a lasting influence. From the Biological Species Concept to the Dobzhansky-Muller-Bateson model of postzygotic isolation, Dobzhansky et al laid a solid foundation for the study of the genetics of speciation. Experimental and theoretical investigations of symbiont-assisted speciation were far and few between as speciation genetics took off in the 80's and 90's by many science idols of mine.
3. Today's biotechnology and thinking are up to the task: With the advent of high throughput sequencing techniques that make the identification of bacterial symbionts simple, and today's recognition of microbial symbiosis as a requirement for complex eukaryotes, Wallin’s ideas on the symbiotic origin of species are primed for a full reassessment. Indeed, the emergence of the bacterial symbiont Wolbachia in topical discussions of speciation (book chapter) was a beginning to reviving Wallin’s silenced ideas. The emerging story supported by the latest science in our review is that biologists have even farther to go with symbiont-assisted speciation. It appears to be almost a given that studies of the general microbial community of animals and plants will reveal even grander ways in which microorganisms act as causative agents of their host's speciation.
4. A new phase in the study of symbiont-assited speciation is happening now: Our article begins begins with a rich, historical controversy in evolution and genetics. Where that debate goes in the future is up for scientific discourse and experimentation. Rob Brucker (@liveinsymbiosis) and I suggest in the review that the current evidence for symbiont-induced speciation is far more solid than many speciation geneticists appreciate, and a new phase of speciation by symbiosis is likely to spur many exciting new insights.

We suggest that as studies of microbe-assisted speciation march forward, Ivan Wallin should be recognized for his pioneering and imaginative work on the microbial basis of speciation. Here is arguably his greatest quote:
It is a rather startling proposal that bacteria, the organisms which are popularly associated with disease, may represent the fundamental causative factor in the origin of species.” (Ivan E. Wallin, 1927)


  1. Hi, Seth... excited to read your review. I'm on the road now, and not able to access the pdf. The topic of your review is an important and interesting one, with a rich history.
    I wonder whether you include the Bellagio Conference in the 1980's organized by Lynne Margulis. It was entitled 'The role of symbiosis in speciation' (or something close to that). Again, I'm on the road and don't have access to the book of abstracts (of the same title) that came out from it. Being a book, of course, it is easily missed in the age of electronic searches!
    Kudos for bringing the topic to the field again.

    1. Hey Ned, thanks for the tip! Im going to have to take a look at that one; it was off my radar. In the past I have been a student of Lynn and Fester (1991) Symbiosis as a Source of Evolutionary Innovation which stemmed from the conference on "Symbiosis as a Source of Evolutionary Innovation". From the looks of it, Margaret, Mary Beth, John Maynard, among others were there.

      I contend (and would love discussion on this) that much of Lynn's work failed to bridge symbiosis and speciation together in a mainstream way because Lynn was speaking a language that was different from the conventional lexicon of the speciation field. Having been fortunate to train w/ Jack and Allen as a grad student, I realized that speciation geneticists equate their traits back to reproductive isolation. Failure to interbreed is the crux of the speciation field, where I believe that Lynn was more interested in studying adaptations. Moving forward, if symbiosis folks talk in terms of reproductive isolation as we do in this TREE article, I think we will have a much more likely chance of fusing the two camps into one. Adaptation does not always equate to speciation, but reproductive isolation does.

      Try this link out. I think I have the preprint uploaded to it.

  2. Hey Ned, I finally dug up your recommendation and it turns out we were talking about the same book ;)

    Symbiosis As a Source of Evolutionary Innovation:
    Speciation and Morphogenesis