Sexually Ambiguous Flies and the Evolution of A Courtship Gene
How do you distinguish a male fly from a female fly? Apparently even flies have problems with this one sometimes, and an interesting paper in PNAS describes a recently evolved gene in fruit flies that reduces the amount of male-male courtship they engage in. A research group based at the University of Chicago found that when you knock out the fly gene sphinix, the flies engaged more frequently in male-male courtship rituals. Flies with their sphinx gene intact will engage in male-male courtship about 1% of the time. But when both copies of the sphinx gene are knocked out, male-male courtship increases in frequency to nearly 8%. As intriguing as this sounds, we've known about genes that impact male-male courtship in flies for some time. What is interesting in this case is that the sphinx gene appears to be a new evolutionary creation, having arisen in the fly species Drosophila melanogaster when a chunk of one gene on one chromosome managed to get transferred into another gene on another chromosome. The resulting chimeric gene shows evidence of being functional - it is expressed only in certain tissues, and its sequence appears to have been shaped by natural selection. And now, in this most recent study, it's clear that sphnix, the recent result of an evolutionary accident, does indeed have a function in shaping courtship behavior. How this gene actually carries out that function is still largely a mystery. So if this chimeric gene sphinx reduces sexual mixups in fly courtship, and if this gene is only present in the species D. melanogaster, doesn't that suggest other fly species should have a higher tendency to male-male courtship? The researchers tested this, looking at courtship behavior in four other fly species. Sure enough, male flies from these other species spent more time than D. melanogaster courting other males. What's going on in terms of evolutionary advantages and disadvantages of various rates of male-male courtship isn't so clear. What is clear though, is that yet again we have an unambiguous example of the creation of a new, regulated, functional gene by an initially random mutation.