Zebra Finch Songs Impacted by the Environment: Nurture, Not Nature

What behaviors are learned and what behaviors are genetic? That's a question that scientists have long sought to tackle. Now, they may have an answer to this question--at least as far as zebra finches are concerned. They've found that these birds' brains and song structures are strongly influenced by the environment rather than just by genetics.

The researchers turned to breeding zebra finch pairs for this particular study. Using partial cross-fostering, the researchers exchanged half of the eggs within a nest making them into "cuckoo's eggs." This caused half of the hatchlings to be raised by their genetic parents while the other half were raised by foster parents. That's not all the scientists did, though. They also modified the availability of food by mixing seeds with husks. This caused the parents to spend more time searching for food.

After 100 days, the researchers then recorded the songs of the male offspring. They also analyzed their underlying neuroanatomy. This allowed them to better see how nature and nurture impacted the birds.

So what did they find? It turned out that heritability values were low for most song characteristics, except the number of song syllables and maximum frequency. This means that the environment was what mainly shaped the bird songs. 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.

That's not all they found. Even more striking results were discovered when the researchers looked at 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.

"Being highly flexible in response to environmental conditions can maintain genetic variation and influences song learning and brain development," said Stefan Leitner, one of the researchers, in a news release.

The findings reveal that the environment has a huge role in influencing the songs and brains of these birds. While previous studies indicated that heritability was the major factor, it seems that variation in the rearing environment might just have more of an influence.

The findings are published in the journal Evolution.