Male fish lose fight, lose girl?
When a fertile female sees her boyfriend get beaten, anxiety fills the aquarium
Female African cichlids like their mates tough. At least that seems to be the case, based on a recent study of the freshwater fish.
When a female cichlid sees her chosen mate win a fight, her brain's pleasure and reproductive centers activate. When she sees him lose, her brain processes an anxiety-like response.
"She's very anxious . . . and may be thinking of an alternative to her original choice," said Julie Desjardins, a Stanford University postdoctoral research associate who spent a year observing how these freshwater females process visual information when picking mates.
In a series of experiments using 15 female and 30 male cichlids, Desjardins and an assistant put a fertile female - whose belly looked swollen with eggs - in the middle section of a clear, compartmentalized aquarium. Two comparable-size males were placed in sections on either side of her.
"In the wild, females that aren't full of eggs only interact" with other females, Desjardins said. "We chose females who needed someone to fertilize their eggs."
Desjardins gave each female 20 minutes over two days to choose a potential mate. She would stare at "the one" through the clear divider and swim near him about 30 percent of the time, more than she swam near the other male.
After the two-day courtship for each female, the scientists put the chosen boyfriend and the reject in the same compartment. Naturally territorial, the two males fought, in full view of the female. In eight cases, the boyfriend won and in seven he lost. Unfortunately for the female, that was the end of her participation: The scientists then dissected her brain and looked for gene activity in the regions responsible for social behavior.
In females that had picked males that turned out to be winners, the brain areas that regulate reproductive hormones (and, ultimately, social sexual behavior) had significant spikes in gene activity. Among females that had picked losers, the brain area that regulates mood and motivation processes such as anxiety had significant increases in gene expression.
When a female cichlid sees the potential father of her babies lose, her brain reacts as if her babies are in danger, Desjardins said. She explored this "genetic early warning system" in a study published online in Proceedings of the National Academy of Sciences in November.
- Leslie Tamura