The finches inhabiting the Galapagos Islands, a volcanic archipelago in the Pacific Ocean off the coast of Ecuador, have played a unique role in evolutionary history. Not only did they evolve in a very specialized way to inhabit the remote region, but they inspired the entire theory of evolution as part of Charles Darwin's breakthrough voyage on the HMS Beagle in the early 1830s.
Now a new study shows that less than 200 years later, Darwin's finches may be at risk of extinction.
According to the study, published on Dec. 18 in the Journal of Applied Ecology, parasitic flies threaten the well-being of the birds, and could potentially wipe them out within several decades. However, University of Utah biology professor and lead author of the study, Dale Clayton, says the news isn't all "doom and gloom."
Clayton said that a "modest reduction in the prevalence of the fly" through human intervention would likely alleviate the extinction rate. Alternatively, he also said the birds could evolve a defense mechanism through natural selection that would make the flies, specifically their larvae, less harmful.
Either way, fighting off these parasitic nest flies—officially known as Philornis downsi and believed to have arrived on the islands in the 1960s—will not be an easy task. They are "pretty nasty customers" according to Clayton, who said the eggs are often laid in the nostrils of the nestlings. Once they hatch the larvae begin feeding, causing perforations through the bill in especially bad cases. Clayton said the flies became especially prominent on the islands in the 1990s.
Clayton told Fusion that while there are other threats to the finches, such as habitat loss, invasive rats that prey on nests and pressure from the tourism industry, the fly is probably the biggest threat at the moment. He said in one part of the study they observed 25 control nests in which none of them fledged for a whole year due to the presence of the maggots.
"That's as bad as it can get," he said.
There are between 14 and 18 species of finch on the Galapagos. The birds express different traits in their beaks depending on the primary food source available on the island they inhabit—this is the trait Darwin identified as being an evolutionary modification.
The study focused on one of the most common finches, the medium ground finch, around 270,000 of which inhabit the 380-square-mile Santa Cruz Island, the second largest island in the archipelago after Isabela. At least one species of finch, the mangrove finch, is already facing potential extinction due to its limited population on a single island.
According to Clayton, if the nest fly can lead to the extinction of a common species of finch, then "the less common species—which have the same fly problem—are likely at risk as well."
As far as potential measures to control the nest fly epidemic, Clayton suggested a few. One idea is to introduce a parasitoid wasp that would lay eggs in the larvae of the fly and then eat them from the inside out. He said while this approach has been used in controlling other parasites, it's very important to make sure the wasp would be host-specific to the fly.
"You don't want to go around wiping out native insects," he said.
Another option would be to use "sterile insect technique" in which the flies are bred in captivity and males are irradiated to be made sterile. They would then be released into the wild, where they could mate with females that would subsequently be unable to lay eggs. But this would require "a lot of sterile male flies," according to Clayton.
In or to determine the risk the flies pose to the finches, Clayton and his colleagues applied a mathematical model based on five years of data to establish the impact flies could have an reproduction rates going forward. The success of finch breeding also depends heavily on food availability, which varies depending on annual rainfall. In modeling three scenarios, they found that in the worst case the birds would no longer exist in 50 years. A more moderate fly infestation scenario gave the finches around a century before extinction.
This may seem like a less-than-imminent demise trajectory, but for a group of birds that has been evolving on the islands for three to five million years, it's a mere blip in the evolutionary timeline. If not for the flies, the end of the finches could be in store due to some other outside factor as human development and environmental degradation have set in motion what is being referred to as the Sixth Extinction. Researchers have estimated that one in six species could be extinct by the year 2100 if current negative environmental trends, such as climate change, continue unabated.
In the meantime, evolution continues; even between the finches and the flies. Clayton said this is referred to as "co-evolution," in which parasites and hosts evolve in tandem in a sort of war of nature to see which species can outdo the other.
"We sometimes refer to this as an arms race," he said.
What would Darwin, the original evolutionary tinkerer, make of all this?
"I think he would be fascinated by the interaction," said Clayton. "I assume he would be very interested in whether the birds can rapidly evolve defenses, which is possible."
Clayton said this evolutionary development of defenses depends on how rapidly genetic mutations crop up and from there get naturally selected into the greater population—a phenomenon that happens less in smaller populations as mutations are rarer.
"We've seen the evolution of defenses in some other populations," he said. "It's just no one really knows how quickly it would occur."