Animated Doodle Video of Wolbachia | Eliminate Dengue Project

As many readers of this blog know, the Wolbachia | Eliminate Dengue Project is a Bill and Melinda Gates Foundation project spearheaded by Scott O'Neill at Monash University in Melbourne.  Ive posted on it recently here. Yesterday, they posted this great animated doodle video for everyone to understand how Wolbachia, a bacterial infection of arthropods, is being used to stop mosquito transmission of dengue virus, the causative agent of Dengue (a.k.a bone break) fever.

Is this serious? You betcha. The World Health Organization estimates that over 40% of the world's population is at risk and a whopping 100 million dengue virus infections occur worldwide each year. Numbers of infection are also on the rise.

ASM's "Small Things Considered" Spotlights Our Article, Speciation By Symbiosis

Over at ASM's Small Things Considered Blog, a very popular blog on all things microbes, Elio Schaechter discusses our recent review entitled Speciation by Symbiosis. I'll start this post by saying that I think the review (coauthored by my student Rob Brucker, @liveinsymbiosis) is one of the most important pieces that Ive contributed to. I'll explain more about that opinion below. Elio is favorable to the article. He highlights some of the key aspects of the review, including:

1. Some of the examples they cite are startling. For one, Wolbachia, like some other bacterial symbionts of insects, induces parthenogenesis in the insect host, a form of asexual reproduction that does not involve fertilization and leads to what is called “asexual speciation

2. For another, Drosophila flies reared on different diets house different microbiota, and show strong mating discrimination; ergo, the symbionts dictate who mates with whom. 

3. Bacterial symbionts that we could classify as vertically-transmitted, nutritional mutualists (e.g., insect symbionts in the genus Buchnera) assist in resource exploitation, thereby creating new ecological opportunities for their host

4. Endosymbionts can also induce cytoplasmic incompatibility.  Here the offspring of infected males and uninfected females are sterile, therefore, unproductive. 

5. In other cases, the offspring of hybrid matings become more susceptible to infection than non-hybrids, which may reduce their fertility and viability. We are working on this very issue right now and plan to have a paper ready in the next few weeks.

This review article was actually a decade in the making for me. Speciation by symbiosis was the topic of my Ph.D. thesis at the University of Rochester and along with Jack Werren, we helped put Wolbachia on the map as one of the first cases by which symbionts drive the evolution of reproductive isolation between species. This work was later followed by several other important studies on Wolbachia and speciation and came on the heels of intense evangelizing by Lynn Margulis that symbionts were important to speciation; though I contend that she actually provided little evidence that directly linked symbionts to speciation. In my opinion, Lynn was more interested in showing that symbionts drive adaptations, an undeniable legacy that she has left behind.

After the Wolbachia-associated speciation work came out, there seemed to be a lull in the pace of work on symbionts and speciation. Within the last few years however and the uptick in microbiome studies in all organisms, it has since become clearer that speciation by symbionts in general is a robust field with many new insights to be gleaned in the future. Symbionts drive mate discrimination in Drosophila, rapid evolution of immune genes that in turn cause hybrid maladies in plants, and directly prevent gene flow between closely related species - all discussed in the paper. Our hope is that the review revitalizes the topic for new and old investigators alike, and that as the merger between speciation genetics and symbiosis become seamless, the pioneer of the idea that symbionts drive speciation, Ivan Wallin, be formally recognized. More on Ivan in our article and ASM Small Things Considered Blog.

Finally, we tried to publish this article as open access at various journals, but it ended up in TREE's hands. If anyone needs a full copy of the pdf, do not hesitate to email me. My email is readily available by google search or the lab home page.

Related blog posts:
1. The story behind Speciation by Symbiosis? (April 26, 2012)
2. Is the microbiome part of the organism or the environment?
3. Is the microbiota species specific? (June 23, 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)