As any Romeo knows, a key to romantic success is knowing when to make your move. For meek tropical fish, this opportunity comes when their macho counterparts disappear. According to a new study, a meek male can become a macho masterpiece in no time, simply by undergoing a dramatic burst of gene expression in his brain. The findings show that social cues alone can trigger a dramatic cascade of biological responses in social animals.
In animals with established social hierarchies, including most primates, dominant males have the easiest time reproducing. Subordinate males have to bide their time, waiting for the right opportunity. Sometimes, however, subordinates can ascend to dominant status, as happens in communities of the cichlid fish Astatotilapia burtoni. Here, meek males have been known to acquire the bright coloring, larger testes, and aggressive behavior of their macho counterparts seemingly overnight. But how and why they do this has been a mystery.
To crack the cichlid code, researchers at Stanford University in California and Duke University in Durham, North Carolina, allowed small groups of male and female fish to interact over a 14 day period. They then removed a dominant male while the fish were in the dark. When the lights were turned on and the subordinate fish could see that the dominant male was gone, some of the subordinates changed color and behavior within minutes, taking on dominant characteristics. The researchers then killed the fish and analyzed them for gene activity in their brains. The team found that expression of egr-1, a so-called "immediate-early" gene that helps trigger later genetic events related to reproductive maturation, more than doubled--but only in the fish that switched from subordinate to dominant status. Both dominant and subordinate fish whose status did not change retained the lower levels of gene expression, the team reports in the November issue of PLoS Biology. The researchers conclude that a change in social opportunity alone was enough to spike gene expression.
Gregory Ball, a neuroscientist at Johns Hopkins University in Baltimore, Maryland, says that he finds this conclusion "pretty convincing." He adds that "we are still only beginning to appreciate how powerful" social clues alone can be. It's possible that other species, including humans, which regularly encounter complex social stimulation also undergo such rapid and dramatic changes in gene expression, Ball says.