White-throated sparrows nest on the ground under shrubs or low in trees. They are one of the most common birds seen in the forest and at suburban bird feeders. Their distinctive song is often likened to the phrase, "Old Sam Peabody Peabody Peabody."
To measure parental behaviors in the birds, Horton recorded the number of feeding trips they made for their young during a specified time. To measure aggression, he recorded their song rate in response to a simulated territorial intrusion: A live sparrow in a cage was displayed in the breeding territory of the wild study subjects, accompanied by the broadcast of a male song.
"The song of the birds is a form of aggression," Horton explains. "They're saying 'get out of my territory.' The rate at which they sing gives a measure of their level of aggression."
The field observations were followed by laboratory analyses of the study subjects, to hone in on differences in their neuroendocrine gene expression.
The researchers focused on ER-alpha as a primary candidate, since it is one of the genes captured by the chromosome inversion and had been previously linked to social behaviors in vertebrates.
Their analyses documented how the genetic differentiation between the morphs affects the transcription of ER-alpha. In one brain region thought to be important for aggression, white-striped birds had three times the level of ER-alpha than did the tan-striped birds. By looking at both the behavioral data and the lab data together, the researchers found the expression of ER-alpha in that region and others predicted variation in territorial aggression and parenting.
"The behaviors that differ between the morphs are known to rely on sex steroid hormones such as testosterone," Maney says. "But we already showed in 2009 that even when their t
|Contact: Beverly Clark|
Emory Health Sciences