By selectively breeding zebrafish, researchers from the Max Planck Institute have found that distinct personality traits can be inherited in as little as two generations. What's more, they found that these inherited features emerge both in behavior and in far-reaching areas of the brain.
Zebrafish are a popular model for studying biological activity. As they are transparent, it is easy to monitor any physiological changes and measure their effects. Adding to this, young zebrafish are capable of a spectrum of behaviors in response to external stimuli. While some may flee in panic when faced with loud sounds, others remain calm. If repeated, some fish learn to ignore the sound, while others never get used to it and perpetually flee.
For this study, researchers mated fish in two distinct groups- those with extremely relaxed behavior when exposed to loud sounds, and those that became extremely skittish. After just two generations, they found that the brains of the fry selected for skittish behavior were significantly different from those of their calmer counterparts.
In particular, the scientists noticed differences in the part of the hypothalamus that contains neurons that secrete dopamine. While this region was only switched on in the more relaxed fish while hearing a loud sound, they found it constantly activated in the skittish fish.
Interestingly enough, the fish also displayed significant behavioral differences during the larval stage- even when not exposed to sound. During this period, the more relaxed fish were also significantly less spontaneously active.
The researchers also noted that when adults, the more relaxed fish tended to adapt much slower than the skittish fish to new environments. The researchers speculate that this may have happened as their more relaxed tendencies may have dampened their stress response.
"The pace at which personality traits can be shifted and fixed in evolution is remarkable," reflects Herwig Baier, one of the study's authors. "The process might be similarly rapid in populations of Homo sapiens."