FOR all that we have learned of the origin of species, there are remarkably few cases where we know the specific genetic change that caused speciation. Now the discovery of a mutation that could lead to two new species of moth provides another one.
Female European corn borer moths (Ostrinia nubilalis) waft a chemical into the air to lure potential mates. After the insects invaded North America in the early 20th century, farmers discovered that pheromone-laced traps could tempt males away from females and from maize crops that the moths infest. This approach worked in the Midwest, but similar traps for moths in New York state did not. In the 1970s, researchers figured out why: New York鈥檚 moths produce a pheromone that is chemically distinct from that of the Midwestern moths. Males are attracted to one or the other, but not both.
鈥淣ew York鈥檚 moths produce a pheromone that is chemically distinct from that of Midwestern moths鈥�
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This difference keeps the two populations from mating in the wild 鈥� an important step towards creating new species. Now a team led by Jean-Marc Lassance and at Lund University in Sweden has identified the gene that is responsible for creating this barrier.
Lassance and L枚fstedt found that the two moth pheromones are composed of fatty acid molecules that are mirror images of one another. The New York moths鈥� pheromone is made up of 98 per cent of one version, the E isomer, while the Midwestern moths make a perfume that contains just as much of the Z isomer. When the two populations mated in the lab, their female offspring produced a more equal mix of the two pheromones (Nature, ).
The team attributes these differences to a mutation in the gene that codes for the enzyme fatty-acyl reductase, which is important in the production of pheromones. Expressed only in females, it comes in two versions, FAR-E and FAR-Z, with the New York moths having FAR-E and the Midwestern moths FAR-Z. Lassance says that this genetic difference is what keeps the two populations from interbreeding.
Questions remain as to how it works. Male moths must develop complementary genetic changes to detect one pheromone or the other, and those genes haven鈥檛 been identified, says , an evolutionary biologist at Cornell University in Ithaca, New York, who was not involved in the study.
But the research adds weight to the theory that pheromones can drive the evolution of new species, Harrison says, and moths probably aren鈥檛 alone. Fruit flies, at least, also do it, and fish and maybe even some mammals use similar odour cues.
