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Gut bugs affect mating

Differences in diet alter the composition of microbiota in Drosophila, which appears to in turn influence mate preferences -- and drive speciation

By | November 1, 2010

Drosophila seem to prefer to mate with other Drosophila raised on the same diet as a result of the bacteria that live in their guts, according to a study published this week in Proceedings of the National Academy of Sciences (PNAS).
Image: Wikimedia commons,
Muhammad Mahdi Karim
These apparent mate preferences, which arose after just one generation, suggest that an organism's microbiota can facilitate rapid evolution and speciation. "It's an interesting paper," said linkurl:Patty Gowaty;http://www.eeb.ucla.edu/indivfaculty.php?FacultyKey=8418 of the University of California, Los Angeles, who did not participate in the study. "The thought that these gut bacteria could be associated with the reproductive outcomes for individuals is fascinating." "There's a lot of emerging research these days about the physiological effects of microbiota, and changes in microbiota in response to environmental conditions," added evolutionary geneticist linkurl:Paul Hohenlohe;http://people.oregonstate.edu/%7Ehohenlop/ of Oregon State University, who was also not involved in the research. "This study ties that into mating preference, too." Twenty years ago, Diane Dodd of Yale University raised Drosophila melanogaster on different media for more than 25 generations and found that those raised on starch media were more likely to mate with other starch-raised flies, while those raised on maltose were more likely to mate with maltose-raised flies. "Nobody understood the mechanism for this, but they understood it was important because mating preference is an early stage of sexual isolation and speciation," said microbiologist linkurl:Eugene Rosenberg,;http://www.tau.ac.il/lifesci/departments/biotech/members/rosenberg/rosenberg.html a professor emeritus at Tel Aviv University in Israel and coauthor of the PNAS paper. "And nothing is more fundamental to evolution than the origin of species." To investigate why these apparent mating preferences arise between flies raised on different diets, Rosenberg and his colleagues first repeated Dodd's experiment using molasses and starch media. Placing together two males and two females, one from each group, the researchers confirmed Dodd's finding that flies tended to mate with other flies raised on similar diets, and found that this nonrandom mating occurred after as little as one generation on the different medium types. The team then treated the flies with antibiotics to rid them of the microorganisms that reside in their guts. Immediately, the flies lost their apparent mating preferences, randomly choosing between molasses-raised flies and starch-raised flies. The results suggested that something in the gut microbiota was driving Drosophila mate preference. It is not clear whether or not these data represent actual mating preferences, however, Gowaty said. "That's one [possibility], but it's not the only one," she said. "When there's more than one male and one female, there's also the possibility of within-sex interactions" that affect which flies mate, such as male-male competition. To determine which bacteria might be driving the nonrandom mating among the flies, the team sampled the microbiota of flies raised on each type of media. One striking difference between the groups was the proportion of a bacterium called Lactobacillus plantarum. While this bacterium made up 26 percent of the microbiota of starch-raised flies, molasses-raised flies contained only 3 percent L. plantarum. When the researchers infected sterile (antibiotic-treated) flies with the bacteria, the mating preferences returned, indicating L. plantarum was indeed influencing the flies' mating patterns. How exactly the bacterium has this effect is uncertain, however, Rosenberg told The Scientist. The team detected significant differences in the composition of the flies' sex pheromones, known as cuticular hydrocarbons, but "this is just a hint that [microbiota] may be working through these sex hormones," he said. "Much more work has to be done to understand the mechanism" by which these bacteria are influencing the flies' sexual behavior. Another important unanswered question that remains is how these mating outcomes affect individual fitness, Gowaty said. Rosenberg and his coauthors suggest that their results fit with a theory of evolution called the hologenome theory, where the unit of natural selection is the "holobiont" -- the organism plus all of its microorganisms, as opposed to just the individual itself. "In order to get variation, which is the raw material for evolution, you can change either the microorganisms or the host," he explained. And because microorganisms can change in response to the environment much more rapidly than the host, evolution of the holobiont may be "an important, driving force, especially for rapid evolution," Rosenberg said. G. Sharon, et al., "Commensal bacteria play a role in mating preference of Drosophila melanogaster," PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1009906107, 2010.
**__Related stories:__***linkurl:Gut sex;http://www.the-scientist.com/article/display/57587/
[August 2010]*linkurl:Spontaneous speciation?;http://www.the-scientist.com/blog/display/55825/
[15th July 2009]*linkurl:Red fish, blue fish, speciation?;http://www.the-scientist.com/blog/display/55065/
[ 2nd October 2008]
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Comments

Avatar of: Mike Waldrep

Mike Waldrep

Posts: 155

November 2, 2010

Interesting!
Avatar of: anonymous poster

anonymous poster

Posts: 5

November 2, 2010

L plantarum is a widespread lactobacillus species, eg in silage including sauerkraut. It occurs in the human intestinal flora, especially in vegetarians (eg, Seventh-Day Adventists), and has been considered a probiotic and used in supplements to improve the intestinal flora.\nRef: http://microbewiki.kenyon.edu/index.php/Lactobacillus_plantarum
Avatar of: Nirmal Mishra

Nirmal Mishra

Posts: 22

November 4, 2010

Drosophila harbor biota in the gut and their occurrence elicits pheromone production which in turn changes propensity for mating. Presence of specific microorganism in the gut may influence pheromone production and this may prompt the fruit flies to mate with those that have similar counterparts. Mere suggestions or a propensity may not lead to speciation. This may affect behavioral characteristics but its impact may not be profound enough to meddle with different gene pools as there are other opposing forces that will come in the way. How will the community of biota promote speciation? If that were so inheritance of acquired characters would heave into view.\nNirmal Kuamr Mishra\nRetd. University Professor of Zoology, Patna University, Patna (India)\n\n
Avatar of: Steven Pace

Steven Pace

Posts: 22

November 13, 2010

@ Nirmal Mishra\nIt is possible that old species like these are very evolved, and use many different indicators of intestinal biota to make all sorts of decisions. In response to your point; as you know, very few genetic changes are visible; in fact, most of them have no known effects. More likely, the changes based on diet would be epigenetic. Epigenetic changes for diet, including total calories, and dietary composition, are well known in humans. The idea that a potential mate could detect them is not implausible.
Avatar of: Chris Toal

Chris Toal

Posts: 1

November 18, 2010

It has been well documented that dietary change introduces change to bacterial populations. Given that the volume and quality of bacterial byproducts dictate many of our health and hormonal functions, it should be expected that a change in bacterial population would engender a change in mating preferences. Most species including humans will not mate with an individual that doesn't 'smell right' and a large component of that smell is driven by diet. Nice work.

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