FIG. 45.8

Can genes influence behavior?

BACKGROUND In fruit flies (Drosophila melanogaster), variation at the foraging (for) gene affects feeding behavior of larvae. Two alleles of the for gene—for^s and for^R—exist in natural populations; for^s larvae tend to stay on a patch of food (“sitters”) and for^R larvae tend to move from patch to patch (“rovers”). Honeybees (Apis mellifera) also forage for food, but, in contrast to fruit flies, this behavior changes with age. Young honeybees stay at the hive (“nurses”), and older ones forage for nectar (“foragers”). The for gene is present in honeybees, raising the possibility that this gene is involved in the developmental change in foraging in honeybees.

HYPOTHESIS Foraging in honeybees is influenced by the expression of the for gene, and nurses have lower expression levels than foragers.

EXPERIMENT 1 Levels of for mRNA were measured in honeybee nurses and foragers.

RESULTS Levels of for mRNA are significantly higher in foragers than in nurses (Fig. 45.8a). However, foragers are older than nurses, so it was unclear whether the increased expression in foragers compared with nurses is associated with differences in age or differences in behavior. Therefore, the experiment was repeated with honeybees that forage at the age at which bees are normally nurses. These young foragers also have higher for mRNA levels than do nurses (Fig. 45.8b).

EXPERIMENT 2 The for gene encodes a cGMP-dependent kinase that phosphorylates other proteins (Chapter 9). Honeybee nurses were treated with cGMP to activate the kinase and their subsequent behavior was monitored. A related compound, cAMP, with a chemical structure similar to cGMP but which does not affect the kinase, was used as a control, to ensure that any effect observed was specific for the pathway and not the result of the treatment.

RESULTS Treatment with cGMP changed the behavior of nurses, causing them to forage (Fig. 45.8c). Furthermore, cGMP acted in a dose-dependent fashion: The higher the dose, the more foraging behavior was observed. No effect on foraging was seen in the control treatment (Fig. 45.8d).

CONCLUSION The same gene that is involved in two different behavioral phenotypes in fruit flies (sitters versus rovers) is also involved in a developmental behavioral change in honeybees (nurses versus foragers). This finding suggests that a gene can have related but different functions in different organisms.

FOLLOW-UP WORK Researchers have looked at the expression of many other genes in the honeybee genome to learn which genes are associated with the change of foraging behavior of honeybees.

SOURCE Ben-Shahar, Y., et al. 2002. “Influence of Gene Action Across Different Time Scales on Behavior.” Science 296:741–744.