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 speciationThis 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.
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.
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)