The phrase, "The way to a man's heart is through his stomach," just got a whole new meaning. A recent study suggests that gut flora could influence an animal's choice of mate.
A team of researchers at Tel Aviv University have been arranging marriages among fruit flies. They've been doing this not through isolation, or hormonal markings, but through diet. Starting with an integrated population of flies, the scientists split them into two groups. One group was fed starch, while another gorged itself on malt sugar. After a generation or two of this treatment, the researchers mixed the groups together again, and found that flies from each group preferred mates that ate the way they did.
This preference was interestings, but could have been caused by a lot of things; scent, habitual behavior, the harsh beauty standards promoted by fly society. The researchers repeated the experiment, separating out the groups, feeding them different diets, and then reintegrating them. This time they added a twist. They gave the flies an antibiotic that killed the bacteria in their digestive system created by their divergent diets. Suddenly the flies weren't nearly as picky about who they hooked up with. The preference for those who shared their own diet was eliminated.
The mechanics of the preference were explored. The researchers studied the pheremones given off by the different populations of fruit flies. Different diets meant different pheremones were given off. When the antibiotics were added, though, the pheremones of both populations became the same once again. This means it wasn't the food putting out the distinctive love stench - it was the bacteria. One of the scientists heading the study, Professor Eugene Rosenberg, believes that evolution is the change of not just one organism, but of a complex group of symbiotic plants and animals; termed a holobiont. The fact that the bacteria inside the fly were steering it towards other flies with the same bacteria means that any long-term change in the fly can be thought of as the evolution of an entire system.
The finding indicates that pheromone alterations are a mechanism by which we can identify mating preferences. We therefore hypothesize that it is the bacteria that are driving this change. Up to now, it was assumed that the host organism undergoes evolution on its own, while its symbiotic bacteria undergo their own evolution. The mechanism that we discovered enables evolution to occur more rapidly in response to environmental changes. Since a generation is shorter for bacteria than for multicellular organisms, they genetically adjust more quickly to changes in the holobiont.
This could change the way people think of evolution. It could also change the way they look at themselves. We may be even less in control of our love lives than we previously thought.