Parasite has caused Darwin’s finches to sing a different tune

By Amy Middleton 29 August 2016
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Darwin’s finches on the Galapagos Islands are evolving rapidly due to an introduced parasite, including developing a new birdsong.

DARWIN’S FINCHES, A unique bird group from the Galapagos Islands, are under threat by an introduced fly parasite.

The larvae of the parasite Philornis downsi was first recorded invading finch nests in 1997. The parasitic flies feed on the tissue and blood of finch nestlings, killing them off in extraordinary numbers.

However, according to a new review by researchers at Flinders University in Adelaide, this deadly relationship is forcing both bird and parasite to evolve rapidly, resulting in hardier finches, some with new beaks – and a whole new birdsong.

Galapagos finches adapt to deadly parasite

Professor Sonia Kleindorfer, a biologist at Flinders University, used 16 years of data to reflect the rapid biological changes occurring in both bird and parasite. Her results were published this month in BMC Zoology.

“Host and parasite are both changing dramatically and quickly over the course of our 16-year study, and each species is exerting mortality pressure on the other,” explained Sonia.

 “This is the only case study in the world for which we have hundreds of vertebrate host specimens from 1900s, before the parasite’s arrival, as well as after its invasion during the 1960s, and detailed field studies for subsequent lethal cascade effects across decades,” she said.

Philornis downsi

Philornis downsi fly. (Image: Kleindorfer Animal Behaviour lab photo by B Sinclair)

Among other shifts, the presence of parasites has changed the shape of the beaks of Darwin’s finches. Parasitic larvae feed in the noses of the nestlings, most of which will die before maturation. Those that survive, however, are left with enlarged nostrils, which persist into adulthood.

Beak changes also elicit shifts in the finches’ birdsong. Preening and foraging may also be affected, but this remains to be tested.

Another interesting shift is the observation of hybridisation – that is, sharing genes across different species, to combat the decline in genetic diversity. Sonia said this process of gene-sharing could be key to a species’ survival in the face of parasitic attacks.

Despite these adaptive changes, the finches remain under serious threat. Along with an international research team, Sonia is also working on programs to eradicate the parasitic fly from Galapagos.

Charles Darwin birds offer clues to parasite evolution

The review contributes to a wider understanding of the dynamics between host and parasite, which could benefit a multitude of birds threatened by parasites, including one Tasmanian species.

“Survival of Tasmania’s Forty-spotted pardalote is threatened by a parasitic fly similar to Philornis downsi,” said Sonia. “Understanding the impacts on the Galapagos will inform how we conserve species across the globe.”

darwin finch

Scientists Jody O’Connor and Sonia Kleindorfer measure a Darwin finch. (Image: Kleindorfer Animal Behaviour lab photo by D Colombelli Negrel)

It’s interesting that secrets of adaptation are still being uncovered via the finches named in honour of Darwin, who is thought to be the grandfather of evolutionary thinking.

“Charles Darwin states that the Galapagos Islands ‘origin all his views’ on evolution by means of natural selection, which many people consider the single most important idea to have been thought by a human being,” said Sonia.

“The fact that our successful global expansion is killing the very treasures that helped us understand the evolution of life is tragically ironic.”

The Galapagos Islands are an archipelago of volcanic islands that lie across the equator in the Pacific Ocean, and represent a hotspot for biodiversity on land and underwater.

Darwin’s finches, also called Galapagos finches, comprise 14 species – all but one of which are found exclusively on Galapagos.

Darwin’s finches were first described by Darwin himself, after his survey voyage on the HMS Beagle in 1835.