S tudy 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
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
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.