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Genetics Reveal History of Songbird Expansion from Australia

Mountain chickadee

NEW YORK (GenomeWeb) – Songbirds appear to have diversified and moved out of Australia via Southeast Asia, according to a study appearing online today in Nature Communications.

Using conserved target sequences from more than 100 songbird species, as well as fossil evidence, researchers from the University of Kansas, Louisiana State University, and elsewhere estimated that songbird diversification began roughly 33 million years ago. The team found that songbirds remained isolated in Australia for around 10 million years after that, eventually spreading to other parts of the world with stops on burgeoning islands in the Indonesian archipelago and elsewhere in Asia.

"Our estimate for the age of songbirds is about half of most previous estimates, placing songbird evolution in a very different geological landscape than previously thought," co-first author Carl Oliveros, a post-doctoral researcher at Louisiana State University, said in a statement. "Thus the previous hypothesis of long-distance dispersal by songbirds from Australia to Africa via Indian Ocean landmasses are put into question because these Indian Ocean islands were submerged by the time we think songbirds diversified."

Roughly half of all bird species belong to the songbird clade oscine — a group that's been traced back to Australia, the team noted. But although songbird origins on that continent have been well established, the history of the clade and the events that led to songbird diversification and distribution around the world are not well understood.

"[Songbirds] are found on almost all corners of the globe, with the exception of Antarctica, and include the familiar crows and sparrows, as well as elaborate singers like mockingbirds and lyrebirds," co-first author Robert Moyle, of the University of Kansas, said in a statement.

In an effort to tease apart murky songbird relationships, the researchers focused on so-called ultraconserved elements. In genomic DNA from 104 songbird species, they captured between 3,096 and 4,644 ultraconserved elements per individual, each sequenced to an average depth of 47.9-fold on the Illumina HiSeq 2500.

The team sequenced the same set of 4,155 ultraconserved elements, spanning some 2.5 million bases, in more than three-quarters of the samples. Using these sequences and clues from the fossil record, the group put together a phylogenetic tree that pointed to a diversification for the songbird clade that was more recent than anticipated.

Since the island of New Guinea is thought to have appeared roughly 12 million years ago, the researchers estimated that when songbirds began venturing out of Australia an estimated 23 million years ago, they may have followed an Asian dispersal route. Their data suggests songbird diversification got a boost from the formation of islands as the Australian continent drifted north, tying together geological and biological events.