Zebra finches form long-lasting pair bonds

Personality differences

Dr. Wolfgang Forstmeier

Individuals of the same species and sex often differ markedly and consistently not only in their appearance, but also in their behavior. This individuality, which we know from a human context as personality variation, is a source of growing interest among evolutionary biologists. In fact, little is known about how these differences are passed down through the generations and what consequences they might have with regard to fitness.

The zebra finch’s high reproductive rate allows us to breed several generations within a couple of years and thereby enables us to study the heredity of "personality differences". Our main focus is on individual differences in sexual behavior. Some males, for example, are particularly aggressive, while others adopt a more peaceful strategy. When courted by a male, some females are prepared to copulate immediately, while others persistently reject all attempts to get close to them. To what extent are these behavioral differences genetically determined, and how are they influenced by the environment? What is the adaptive value of such individuality?

It has been suggested that offspring personality could be subject to "strategic programming" by the mother (known as maternal effects, e.g. mediated via deposition of sex hormones in the eggs). Such a mechanism could offer e.g. male descendants a significant advantage in terms of selection: given a social system with a balanced sex ratio and infrequent contact between neighbors, monogamous males of a "good-parent type" should have an advantage, since they can invest all their energy into caring for their brood. However, when the sex ratio is female-biased, males with a strong sex drive should have an advantage, and when the sex-ratio is male-biased, aggressive males are expected to have the upper hand. We study whether maternal effects on offspring behavior are consistent with such a scenario of adaptive programming in relation to the social environment.

Initial findings indicate that there is considerable flexibility in the proximate determination of behavior. Even slight changes in environmental or breeding conditions seem to alter what we believe to be fundamental patterns of heredity. A particular challenge in this context is to find out which aspects of the environment sometimes lead to visible maternal or genetic effects and sometimes make them disappear. As part of our investigations, we want to empirically test various hypotheses around the individual diversity of behavioral phenotypes.

Go to Editor View