Bird evolution has helped scientists understand how natural selection works since the time of Darwin. Find out how a species of birds in Indonesia demonstrated how rapidly evolution can take place.
Bird evolution has a long tradition of teaching scientists about the processes of descent with variation and natural selection. Beginning with Charles Darwin in the Galapagos Islands, biologists have looked to changes in bird species to shed light on the processes driving biodiversity.
Charles Darwin took part in a survey voyage aboard the HMS Beagle between 1831 and 1836. His most famous research aboard the Beagle was probably his work on the isolated Galapagos Islands in the Pacific Ocean.
Darwin gathered 26 specimens of finches from the Galapagos Islands, which he donated to the Zoological Society of London. Ornithologist John Gould explained to Darwin that he had discovered an entirely new group of finches containing 12 unknown species.
Dawin gathered 26 specimens of finches
In his book The Voyage of the Beagle, Darwin wrote, “It is very remarkable that a nearly perfect gradation of structure in this one group can be traced in the form of the beak, from one exceeding in dimensions that of the largest grosbeak, to another differing but little from that of a warbler.”
These changes in beak structure were central to Darwin’s development of his theory of evolution. As he explained in the book’s second edition, “Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”
In his landmark On the Origin of Species, Darwin went further in outlining bird evolution, writing, “The Galapagos Islands would be likely to receive colonists, whether by occasional means of transport or by formerly continuous land, from America…and that such colonists would be liable to modification — the principle of inheritance still betraying their original birthplace.”
Species originate from natural selection
From these observations, Darwin concluded that species originate as a result of descent with modification in the context of natural selection. He called this process evolution.
In the tradition of Darwin, researchers from Trinity College Dublin have just published a study in Zoologischer Anzeiger: A Journal of Comparative Zoology. It describes how their work with birds expands our understanding of the evolutionary process. Zoologists from Trinity’s School of Natural Sciences have been observing a bird species called the Sulawesi Babblers in the islands of Indonesia.
The islands where the Sulawesi Babblers live are comparatively recent in geological terms. There used to be land bridges between them, and these disappeared roughly 30,000 years ago.
Habitat Quite Different From Darwin’s Finches
This makes these birds and their habitat quite different from Darwin’s Finches. Ph.D. candidate Fionn O’Marcaigh is the first author of the research paper. He explained the distinction like this.
“Everyone has heard of Darwin’s finches evolving completely different bill shapes on the Galapagos islands. The Galapagos are isolated out in the Pacific, so the birds there have had millions of years to evolve separately. Unlike the Galapagos, the islands we looked at are just 20 km or less from the mainland.”
The researchers measured the birds, recorded their songs and sequenced their DNA. During their short period of isolation, bird evolution has caused a genetic variance of up to 1/3 of that seen in distant relatives. This is even though they separated from these foreign species millions of years ago.
One percent of the time, 33% of the differentiation
So, in just one percent of the time, the Sulawesi Babblers’ DNA shows 33% of the differentiation. That’s a much faster rate of change than the scientists expected to find.
The reason for this rapid bird evolution seems to be because of the babblers’ lifestyle. They’re shy feathered creatures who live in the forest underbrush called the understorey.
The babblers are physically capable of flying from one island to another, but they choose to stay where they are as a rule. O’Marcaigh explains, “Sometimes evolution can occur on much smaller scales of time and space.”
Body Shape,Song, DNA Subtly Changing
The changes that the team detected due to bird evolution aren’t apparent to the untrained eye. The babblers still look so similar that scientists consider them all one species. Even so, the findings show that the birds’ body shape, song and DNA are subtly changing.
A specific rock type drives this rapid change. They’re called ultramafic (mineral-rich) rocks, and on certain islands, they contain large quantities of nickel.
The nickel makes its way into the soil and changes the species of plants that can grow in the ecosystem. The birds are gradually adapting to these shifts in soil composition.
Threat to the Bird Populations
This poses a threat to the bird populations because mining companies are vying to extract the nickel from the islands’ rock formations. Commercial mining operations could eliminate the Sulawesi Babblers’ habitat before zoologists even have a chance to map the region’s biodiversity.
Evolution provides humans with a new story about how we came to be here. Yet, for many of us, the narrative can be counterintuitive.
It’s challenging for us to understand how such rich global diversity could have arisen over any timescale. This is partly because our short lifespan makes the glacially slow process hard to grasp. The rate of change also varies enormously by time and place.
Shows How Rapidly Speciation Can Progress
Bird evolution on Sulawesi and its neighbouring islands shows how rapidly speciation can progress. In addition, the researchers point out that zoologists have seen similar patterns among mammals and amphibians in the region.
The islands are part of an area called Wallacea, which is known for its intense biodiversity. As with other ecologically significant sites worldwide, governments need to conserve Sulawesi and its neighbouring islands. This will allow researchers to learn more about how our natural world works.
In their study, the team concludes, “Time is therefore running out to build a full picture of the biodiversity of these islands and their evolutionary dynamics.”
Emergence of New Species Drives Biodiversity
The next step for the researchers is to determine which areas within the threatened Wallacea biodiversity hot-spot are the most significant in creating biodiversity. The emergence of new species is what drives biodiversity within an ecosystem.
Fionn O’Marcaigh concluded, saying, “The more we study biodiversity, the more we realize is out there, as species and islands that have never been examined closely can turn out to be full of surprises.”
We always have more to learn if we dare to know.
Learn more:
Rapidly diversifying birds in Southeast Asia – the Sulawesi babblers are teaching us fresh things about evolution
Evolution in the understorey
The Origin of Species and the Voyage of the Beagle
Origin of Life Before the Origin of Species: Four Theories
What Causes Tropical Biodiversity?
