Hans-Peter Lipp , University of Zurich

room 815, Mayer Building at 15:30

17 June, 2010
Genetic and developmental roots of behavioral individuality:  an evolutionary perspective

Given the complexity of the mammalian brain and its inherent plasticity, a main conceptual problem in genetics of brain and behavior is how single genes and simple epigenetic mechanisms achieve significant and long-lasting expression in order to determine neural and behavioral traits. The problem can be at least partially resolved, if one assumes that brain development reflects a building up of a system hierarchy, which is itself characterized by interconnections of system set-points rather than by a network connecting all components of the brain. Thus, primary targets of genes or epigenetic factors influencing the operation of given systems must be set-points. But how can such factors be specific for behavior and behavioral traits, particularly so if one assumes that most gene mutations have detrimental effects?

A possible answer is timing: early effects, predominant during intrauterine development and affecting basic properties of neurons and connections, tend to produce neurological syndromes; while during the middle stages of development, many such effects are masked by system homeostasis, developmental and adult plasticity.  On the other hand, the very last steps of differentiation  occur postnatally when genes or epigenetic factors can influence only the last steps of functional differentiation, that is the implementation of talents and propensities. From an evolutionary perspective, this results in differential accumulation of genetic variation of brain-specific mutations: early-acting mutations reducing biological fitness are constantly eliminated by natural selection; mutations acting during the middle developmental period hardly achieve phenotypic expression and are thus protected and accumulated. Finally, mutations and epigenetic factors acting during the last developmental period do often not affect biological fitness but are no longer modified by developmental plasticity. Therefore, they are more visible and appear as personality traits. They also become, depending on the ecological situation, the prime target of natural selection, allowing rapid evolutionary remodeling of the cerebral system hierarchy according to a top-to-bottom principle.

While simplistic, this concepts allows to understand:
- How mammals can maintain a high rate of evolutionary change
  despite of the complexity of their brains.
- How single genes can modify specifically cognitive and emotional traits.
- How such stable traits are equally vulnerable to epigenetic factors
  or even random events during brain late brain development.
- Some phenotypic peculiarities of genetically modified mice.

The concept shall be illustrated by studies monitoring the microevolution of the hippocampal mossy fiber system in naturalistic environments in Western Russia
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