Thursday, September 1, 2016

How songbirds island-hopped their way from Australia to spread their wings across the world

The songbirds that are common in gardens all across the world have a surprisingly distant origin. They all evolved from a common ancestor that emerged from what is now Australia around 24m years ago. How they managed to leave this isolated part of the world and spread all over the planet has long been a mystery to scientists. But a new study suggests they began spreading just as the islands in and around Indonesia were being formed, creating a pathway for them to cross what had previously been thousands of kilometres of open ocean.

Songbirds are a tremendously diverse group of small perching birds, made up of over 5,000 known species distributed across the world. Common examples include the European robin (Erithacus rubecula) and the North American song sparrow (Melospiza melodia). Together, songbirds account for almost half of all bird species alive today.

Although fossils of birds are rare, the ancestor of all songbirds is thought to have originated in Australia, at a time when the Australian landmass was separated from all other land by a vast ocean in all directions. So, despite the birds' extensive evolutionary spread, it remained unclear how this diverse and cosmopolitan family arose from a single ancestral species on an isolated continent.
However, a recent study by researchers at the University of Kansas and published in the journal Nature Communications sheds new light on this question. Using genetic and fossil data, the authors reconstructed the evolutionary “family tree” for songbirds. They then linked this to information on different species’ geographic locations to understand how early songbirds spread between different continents over the course of millions of years.

This confirmed that songbirds originated in Australia just over 30m years ago. But the most eye-catching finding is that songbirds started to spread out of Australia much more recently than previously thought. This process appears to have started approximately 24m years ago, at the same time as the formation of Wallacea, a group of islands bridging the ocean-filled gap between Australia and Asia. So this may explain how songbirds were able to leave Australia and radiate across the rest of the world, by island-hopping their way to Asia… read more: