Dr. Rosemary Grant, along with her husband, Peter, stunned the world of evolutionary biology in the 1980s and 1990s with the discovery of just how quickly natural selection could shape and reshape the physical attributes (or “phenotypes”) of animals. They have worked with several species of Darwin’s finches in the Galapagos Islands for more than 40 years. The pair made waves again in 2017 with the discovery of a new lineage of finch—possibly an incipient species—that developed from a hybrid over just the last three decades.
Dr. Grant spoke at Cornell on March 12, 2018, kicking off the Paul C. Mundinger Distinguished Lectureship (see sidebar). Her talk was entitled Evolution of Darwin’s Finches: Integrating Behavior, Ecology, and Genetics—watch an archived video of the talk.
Dr. Grant is a senior research biologist emerita at Princeton University and a hero to generations of students and scientists. Her work has been used as a classic example of evolution in action for countless high-school and college biology classes. She kindly answered a few of our inquiries about research and life on the Galapagos Islands, and the never-ending supply of questions she has found there:
Q: How did you wind up doing your life’s work in the Galapagos?
RG: Darwin’s Origin of Species ends with that wonderfully poetic sentence
There is grandeur in this view of life, …that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
This led to my burning questions: how does biodiversity arise, what are the processes that lead to new phenotypes and eventually to new species? Peter and I met when we were 23; I had more of a genetic background and Peter more of an ecological background, but we both had the same overarching questions, and the Galapagos proved to be the best place to look for answers.
Q: What are the best and worst parts of spending a field season on a small volcanic island on the equator?
RG: The best parts are living amongst your study animal in its environment. Every day there are new and stimulating questions posed. Not only about the finches, but about the plants, insects, etc., and all the huge diversity of life that surrounds you, with no distractions from the outside world. It is magical.
The worst part…well it is nice to have a warm freshwater shower and to eat fresh fruits and vegetables when you return.
Q: What’s so special about Darwin’s finches that allows you to ask and answer deep questions about evolution?
RG: Both Darwin and [Alfred Russel] Wallace pointed out that a group of related organisms that have all recently been derived from a common ancestor (we now call these adaptive radiations) would be rewarding places to examine changes that could lead to the formation of new phenotypes. The Darwin’s finches have four important advantages for such a study:
- The radiation is young—the finches have all been derived within the last two million years.
- The species occur together and separately on islands that differ from each other ecologically, in essence setting up a whole range of natural comparisons and contrasts for us to make.
- Many of these islands are uninhabited and close to pristine, so any changes we observe and measure are the result of natural causes.
- Finally, seated astride the equator they are subject to years of intense rainfall (El Niño years), when the finches breed profusely, interspersed with droughts (La Niña years), when up to 90% of the finches die. By studying the types of food available during droughts, who dies, and who survives, we have learned an awful lot about natural selection.
Q: Perhaps your best-known research involves the discovery of natural selection acting on beak sizes much faster than had been previously thought possible. At what point did you realize you were on to something really new?
RG: We had hoped to unravel the reasons for the maintenance of such large phenotypic variation seen in Geospiza fortis on Daphne and conirostris on Genovesa. We did not realize the magnitude of the changes we would be able to measure. At the onset of the 1977 drought and as birds were dying due to lack of small soft seeds we did immediately see the possibility that there might be differential survival and that bigger birds with larger beaks were surviving because of their ability to crack the large hard tribulus seeds.
Q: Which is your favorite Darwin’s finch (or other Galapagos bird) and why?
RG: I’m more fond of individual birds than of one favorite species. Darwin’s finches are very tame. We band them with a unique combination of color bands, and one numbered metal band, so it is easier to recognize individuals. My favorites have been the hybrids because they have revealed so much that was unexpected when we first visited the islands.
Q: Do you think hybridization—once thought of as an anomaly or dead end—has been unfairly overlooked in the past?
RG: It was known that hybridization played an important role in plant speciation, but was thought that hybridization in animals was unimportant. Many animal hybrids were at a survival and reproductive disadvantage compared to the parental species in the same environment. What was missing was the realization that hybridization followed by backcrossing to one or other of the parental species could enhance genetic variation and in a changed environment could fuel rapid changes, along a different trajectory. Lewontin and Birch wrote an important paper in 1966 that demonstrated that a Dacus fruit fly in Australia was produced in this way, in the wild, and led to a population that could survive and breed at higher temperatures than either parental species. This paper received relatively little attention for about 30 years.
Q: What would you ask Charles Darwin if you had the chance?
RG: I would love to have a conversation with Darwin about the new genetic techniques that are now available and how they would have impacted his ideas.
Q: Your talk is subtitled “Integrating Behavior, Ecology, and Genetics.” Can you give us a preview of what ties those fields together in your work?
RG: In order to understand and interpret evolutionary change it is necessary to take into account the gene–environmental interaction throughout the life of individuals. The environment is not just the physical environment, that is, vegetation changes in response to climatic changes. It’s also the social environment, that is, interactions with members of its own and other species. My talk will illustrate how it is necessary to take all these factors into account in order to understand the changes in phenotypes we have witnessed over our 40 years of study.
The other reason I chose this title was that my talk is in honor of Paul Mundinger (see sidebar) who was well aware of gene–environmental interactions and whose research on bird song demonstrated how song, a learned culturally transmitted trait can be modified by genetic differences between individuals.
Q: Do Darwin’s finches still surprise you after more than 40 years of close study?
RG: Yes, we are still gaining insights and there are still many questions to ask. Some of these come from the new genetic techniques we have access to. But there are other burning questions. For example, what are the genetics and neural pathways underlying the ability of the finches to learn their song in such a short period of time early in life? Why can they copy other Darwin’s finch songs but not the songs of other species like the Yellow Warbler that lives on the same island? Some Darwin’s finch species live in the cloud forest on the higher islands; others only in the arid lowlands; and still others (on Cocos Island) live in a wet tropical rainforest. What are their physiological adaptations? I could list a hundred more questions.
Q: What sort of advice do you have for aspiring field biologists just starting out, in a world where so much is possible in the lab?
RG: For any biologist, or indeed anyone with a passion to follow their own burning questions, I would say follow your heart. The path will not be smooth but there will be magic in it. Also take heed of the exceptions to a favored theory—it is often by following your exceptions that valuable insights are revealed.
And I will also end my talk with this: We live in exciting times when genomic data are rapidly accumulating. This enhances our studies but, reciprocally, a reliable interpretation of genetic data requires an understanding of ecology, evolution, and behavior in the natural world.
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