After more than 20 years of debate and not much data, researchers may finally have found an example of what has been colorfully referred to as a green-beard gene. The discovery was made in fire ants, who attack and rip to pieces some of their own queens.
Ants bearing the gene do not really sprout emerald goatees, although codiscoverer Laurent Keller of the University of Lausanne in Switzerland admits that in moments of enthusiasm he has included a colored tuft on a lecture slide.
Exactly what the gene does is not clear, but it creates some recognizable physical sign, perhaps an odor, say Keller and Kenneth G. Ross of the University of Georgia in Athens. Whatever the cue, ants seem able to tell which variation of the gene their queens carry.
The gene under study comes in two forms, or alleles, that the researchers label B and b. All ants carry two copies of the gene, and any queen with the BB combination gets mobbed and killed just before she's ready to start laying eggs, Keller and Ross report in the August 6 Nature. That slaughter makes the b allele more likely to continue into the next generation; any queen who lives long enough to lay an egg must carry at least one copy.
After examining more than 2,500 mature egg-laying females in wild multi-queen colonies, Ross reports finding no BB's.
Another oddity ensures that the b allele doesn't ultimately replace B, however. Ants with the bb configuration, whether workers or queens, die early in life. Researchers don't know why.
The queen-killing behavior fits a view of genes as selfish, the molecular equivalents of gangsters who hustle to get the biggest advantage. …