Study argues efforts to control parasitic fly may save birds critical to inception of Darwin's theory of evolution
New UMass Dartmouth Biology Assistant Professor Jennifer Koop is a co-author of a new study through the University of Utah, which outlines mathematical simulations showing parasitic flies may spell extinction for Darwin’s finches in the Galapagos Islands. Pest-control efforts, according to the study recently published in the Journal of Applied Ecology, might save the birds that helped inspire Charles Darwin’s theory of evolution of natural selection.
The new study “shows that the fly has the potential to drive populations of the most common species of Darwin’s finch to extinction in several decades,” said University of Utah Biology Professor Dale Clayton, senior author of the study. But the research “is not all doom and gloom,” he adds. “Our mathematical model also shows that a modest reduction in the prevalence of the fly – through human intervention and management – would alleviate the extinction risk.”
“Darwin’s finches are one of the best examples we have of speciation,” Professor Koop, who served as first author on the study and conducted research as a University of Utah doctoral student before joining UMass Dartmouth. “They were important to Darwin because they helped him develop his theory of evolution by natural selection.”
The new study is based on five years of data collected by Professor Koop, Dr. Clayton and colleagues documenting fly damage to finch reproduction, and on mathematical modeling or simulation using that and other data. The study was performed on Santa Cruz Island in the Galapagos. An estimated 270,000 medium ground finches live on that island and perhaps 500,000 live throughout the Galapagos Islands.
Darwin’s finches live only in the Galapagos Islands, off the coast of mainland Ecuador. The finches began as one species and started evolving into separate species an estimated three to five million years ago. The new study dealt with medium ground finches among the most common of at least 14 species of Darwin’s finches. One of them, the mangrove finch, already is facing potential total extinction because it is present in only two populations on a single island.
Several approaches may be needed in pest-control efforts, such as introducing fly-parasitizing wasps, removing chicks from nests for hand-rearing, raising sterile male flies to mate with females so they can’t lay eggs in finch nests, and using insecticides, including placing pesticide-treated cotton balls where birds can collect them to self-fumigate their nests.
The case of the flies and finches exemplifies how “introduced pathogens and other parasites pose a major threat to global diversity,” according to the researchers’ writings, especially on islands, which tend to have smaller habitat sizes and lower genetic diversity. In addition to the medium ground finch, other abundant species of Darwin’s finches are the small ground finch, cactus finch and small tree finch.
To simulate such highly variable conditions and how they affect the probability of finches fledging from a fly-infested nest and thus population growth, the researchers used data from five years – 2008, 2009, 2010, 2012 and 2013. They ran three simulations: one weighted toward bad years for breeding and survival, one weighted toward good years and one equally weighted.
The researchers concluded that in two of the three scenarios their model predicted that medium ground finch populations on the island of Santa Cruz were declining and at risk of extinction within the next century. The significant role of nest infestation in extinction risk has an upside for medium ground finches.
“Even though these guys may be going locally extinct, the model also shows that if you can reduce the probability of infestation, then you significantly alleviate the risk of extinction,” Dr. Koop said.
Professor Clayton added, “If we can reduce the number of nests with the flies, then it will reduce the risk of extinction substantially.”
The simulations showed that a 40 percent reduction in fly infestation of nests would extend the predicted time to extinction by 60 years, which would mean more than 100 years to extinctions in the two gloomy scenarios. Predicted extinction times more than 100 years in the future are considered too uncertain and thus aren’t considered as valid predictions of extinction.
The researchers reason it is possible a rapid evolutionary response by the birds and their immune systems could develop the ability to combat the fly.
“That happens in other animals. The question is, will these finches have enough time to develop effective defenses before they are driven to extinction by the fly? It’s an arms race,” said Dr. Clayton.
The study was funded by the National Science Foundation, Sigma Xi, the Scientific Research Society, the National Institutes of Health, the Australian Research Council, the University of Utah Global Change and Sustainability Center, and a Frank Chapman grant from the American Museum of Natural History.
Koop and Clayton conducted the study with Fred Adler, a University of Utah professor of mathematics and biology; former Utah biology doctoral student Sarah Knutie, now at the University of South Florida; and former Utah mathematics postdoctoral fellow Peter Kim, now at the University of Sydney, Australia.
Jennifer Koop is an Assistant Professor in the Biology Department. Her research focuses on understanding the establishment and transmission-virulence dynamics of host-parasite interactions in which one or both species are considered to be invasive. She received her Ph.D. in Biology from the University of Utah where she worked in the Galapagos on Darwin’s finches. Most recently, she completed an NIH-postdoctoral fellowship at the University of Arizona working on systems in the Galapagos and desert southwest.
Editor's Note: Photos used in article courtesy of the University of Utah.