Scientists devise new model for origins of Darwin’s finches

May 9 (UPI) — New research offers the best explanation to date of the origins of Darwin’s finches.

The diversity of finches on the Galapagos Islands inspired Darwin’s theory of natural selection and species divergence, central tenets of the naturalist’s theory of evolution. But until now, scientists have struggled to determine where the finch species came from and how they got to the Pacific Islands.

Darwin’s finches include 15 passerine species. They belong to the tanager family and are not closely related to true finches.

As part of the latest study, San Diego State University’s Erik Funk and Kevin Burns built a complex statistical model to consider two competing hypotheses for the origins of Darwin’s finches. Both models considered the Galapagos, South America and the Caribbean as the birds’ true origins, but one of the models divided the regions into subregions grouped by common plants and animals.

The more detailed model, which considered the unique ecologies of the Amazon and the Andes, predicted the finches came from the Caribbean, not the South American mainland. The slightly simpler model, which considered five regions instead of eight, showed the birds came from mainland South America.

Researchers suggest the findings of one model are not more or less likely than the other.

“I think one of the big take-away messages here is the possibility that biogeographic events, like dispersal, may not necessarily happen like logic tells us they should,” Funk said in a news release. “Darwin’s finches are such a highly studied group, and it is often taken for granted they arrived from mainland South America, but hopefully our results show readers that there is no more support for this hypothesis than there is for a Caribbean origin.”

The birds’ origins remain uncertain, but researchers believe they can account for the birds’ successful colonization of the Galapagos Islands. Scientists argue the finches were more likely to wander than other close relatives, and thus, more likely to encounter new territory. Additionally, the birds boast greater genetic variation in bill size and shape than their peers, allowing them to adapt more easily to newfound territory with foreign food resources.

By examining the origins of Darwin’s finches, scientists can better understand how species move and how these patterns of biogeography impact the species’ evolution.

Researchers detailed their work in the journal The Auk.

“In 2018, we still have fundamental things to learn about one of the most studied and celebrated groups of birds, Darwin’s finches,” said researcher Shannon Hackett, a curator and avian expert at the Field Museum in Chicago. “Perhaps we should be calling them Darwin’s tanagers because it is Burns’ tree of life for these birds, nesting them firmly in tanagers, that is enabling new insights into the evolution, morphology and origins of this remarkable group of birds.”