14 DAY TRIAL // "Oh, no, honey, it's about technique!" says your girl. Is it so? Some fish come with the pure truth: size does matter!
In the case of the swordtail, a common tank fish, the simple sight of a well-endowed male turns off an entire families of genes (about 77 genes overall) in the female's brain, as a team at the University of Texas at Austin has found in a study published in the Proceedings of the Royal Society of London B. Surprisingly, much more genes are turned off than on. The largest most attractive males provoked the most intense genes to shut down while smaller males cause a weaker response. When the females were placed close to another female, the same genes inhibited in the presence of males were activated and vice-versa.
This change in gene activity modifies female's behavior, as she turns more daring for gaining the stud's attention. And the best studs in the swordtail world are those adorned with body ornaments, such as long Tails and bright coloration.
After repeating fish-tank experiments, the team discovered that when an attractive swordtail male was around, some of the female genes that were connected with sexual behaviors changed activity. The shift in the genes' activity took place in just 30 minutes, rapidly enough so the well endowed male could lure the female with body ornaments and copulate with her (swordtail and their relatives represent a rare case of internal fecundation in bony fish). Analysis of RNA extracted from the females detected genes that were being turned on or off in the females' brains.
"We've found a number of new genes that haven't been implicated in mating behavior before", said co-author Hans Hofmann, assistant professor of integrative biology.
"What we have not appreciated until now is how dynamic the genome is. It is constantly changing and even in a very short period of time, 10 % of the protein-coding genome can change its activity. We now have a genomic view of these dynamic processes within a social context", he added.
The shut off genes could have a crucial role in inhibiting sexual behavior. Perhaps when this activity is inhibited, the "chastity belt" of females is thrown away, enabling them to go for males.
"In the presence of the attractive male, [these genes] are inactivated and as a consequence this inhibition goes away", Hofmann told LiveScience.
This research is one of the few connecting changes in the gene expression to those in an individual's behavior in various situations, and the same gene sets could be linked to mating responses in all vertebrates. The team aims to detect specific brain nuclei where genes activity changes.
