Like father, not like son: Brain and song structure in zebra finches are strongly influenced by the environment

An attempt to tease apart these effects has been conducted by researchers from the Max Planck Institute for Ornithology in collaboration with an international team of scientists in zebra finch breeding pairs. Using partial cross-fostering the researchers exchanged half of the eggs within a nest making them to “cuckoo’s eggs”. Therefore half of the hatchlings were raised by their genetic parents, whereas the other half was raised by their foster parents. In addition they modified the availability of food by mixing the seeds with husks so that the parents had to spend more time searching for food. When the male offspring were adult at 100 days the researchers recorded their songs and analyzed the underlying neuroanatomy. This partial cross-fostering design enabled the researchers to tease apart the involvement of genotype, the rearing environment and nutritional effects to variation in song behavior and brain structure.

The results showed that heritability values were low for most song characteristics, except the number of song syllables and maximum frequency. On the other hand the common rearing environment including the song of the foster father mainly predicted the proportion of unique syllables in the songs of the sons, moreover this relationship was dependent on food availability. Even more striking results were found when the researchers investigated the brain anatomy. Heritability of brain variables was very low and strongly controlled by the environment. For example, an emergence of a clear relationship between brain mass and genotype is prevented by varying environmental quality.

This result was quite surprising as previous studies have found a high heritability of the song control system in the songbird brain, however these studies did not account for variation of the rearing environment. ”Being highly flexible in response to environmental conditions can maintain genetic variation and influences song learning and brain development” says Stefan Leitner, senior author of the study.