Wild songbirds are beautiful little creatures that make time spent in our backyard a lot more fun. They sing melancholic songs which will put your mind to ease. However, not many people know that songbirds sing to claim territory. The song communicates about their identity and even their sexual intentions.
The latest study reveals how differentiation in a single gene can alter behavior in wild songbirds. It shows how the sparrow displays aggression. The research was published by the Proceedings of the National Academy of Sciences (PNAS). It was led by the Emory University neuroscientists. An estrogen receptor was singled out from a complex of over a thousand genes that are referred to as a ‘supergene’. It is a genetic material that has been inherited together by the block. Thus, the study offers rare insights into how genomic divergence could cause behavioral divergence in vertebrates.
Jennifer Merritt, an Emory graduate who is the first author of the study stated that evolution changes the DNA sequence of a gene of the songbird. The changes impact both the behavior of the bird and its way of expression. White-throated sparrows are known to be the most common birds found in a backyard across North America. A remarkable thing about the two different morphs is that they are not just different plumage but that there are also different strategies that maximize the reproductive output.
The differences are a result of genetic differentiation of one region of a chromosome. At any point during evolution of a species, the chromosome can easily break and flip. It is a process which is known as inversion. It is where isolates which are trapped inside end up producing a supergene. There are some cases where supergenes caused distinct morphs within the same species. Thus, it results in individuals without the supergene and those with it.
As for white-throated sparrows, the tan-striped morph has muted grayish stripes, whereas, the white-striped morph has black, bright yellow, and white stripes right at its crown. The white-striped birds possess at least a copy of a rearranged chromosome. It is what makes them more aggressive and even less parental as compared to tan-striped birds that do not have any rearranged chromosome.
In 2014, the lab identified the estrogen receptor alpha(ER-alpha) that connected to agrresion and parenting behaviors of wild sparrows. White-striped birds which were blocked ER-alpha gene, the aggression went down so they behaved like the tan-striped ones. The researchers found that the more a white-throated sparrow expresse the supergene version of the estrogen receptor, the more strongly it defends its territory.
“We believe this is the first demonstration of how a single gene within a supergene drives changes in a social behavior in a wild vertebrate,” Merritt says.
Further research is being conducted by the Maney Lab to gain more insights regarding white-throated sparrow chromosome rearrangement.