Why the Galápagos Islands and the islands finches were helpful to Darwin in developing his theory of natural selection?

The arrival 36 years ago of a strange bird to a remote island in the Galápagos archipelago has provided direct genetic evidence of a novel way in which new species arise.

On Nov. 23 in the journal Science, researchers from Princeton University and Uppsala University in Sweden report that the newcomer belonging to one species mated with a member of another species resident on the island, giving rise to a new species that today consists of roughly 30 individuals.

The study comes from work conducted on Darwin’s finches, which live on the Galápagos Islands in the Pacific Ocean. The remote location has enabled researchers to study the evolution of biodiversity due to natural selection under pristine conditions.

The direct observation of the origin of this new species occurred during field work carried out over the last four decades by B. Rosemary Grant and Peter Grant, a wife-and-husband team of scientists from Princeton, on the small island of Daphne Major.

"The novelty of this study is that we can follow the emergence of new species in the wild," said B. Rosemary Grant, a senior research biologist, emeritus, and a senior biologist in the Department of Ecology and Evolutionary Biology. "Through our work on Daphne Major, we were able to observe the pairing up of two birds from different species and then follow what happened to see how speciation occurred."

In 1981, a graduate student working with the Grants on Daphne Major noticed the newcomer, a male that sang an unusual song and was much larger in body and beak size than the three resident species of birds on the island.

"We didn't see him fly in from over the sea, but we noticed him shortly after he arrived. He was so different from the other birds that we knew he did not hatch from an egg on Daphne Major," said Peter Grant, the Class of 1877 Professor of Zoology, Emeritus, and a professor of ecology and evolutionary biology, emeritus.

The researchers took a blood sample and released the bird, which later bred with a resident medium ground finch of the species Geospiz fortis, initiating a new lineage. The Grants and their research team followed the new "Big Bird lineage" for six generations, taking blood samples for use in genetic analysis.

In the current study, researchers from Uppsala University analyzed DNA collected from the parent birds and their offspring over the years. The investigators discovered that the original male parent was a large cactus finch of the species Geospiza conirostris from Española island, which is more than 100 kilometers (about 62 miles) to the southeast in the archipelago.

The remarkable distance meant that the male finch was not able to return home to mate with a member of his own species and so chose a mate from among the three species already on Daphne Major. This reproductive isolation is considered a critical step in the development of a new species when two separate species interbreed.

The offspring were also reproductively isolated because their song, which is used to attract mates, was unusual and failed to attract females from the resident species. The offspring also differed from the resident species in beak size and shape, which is a major cue for mate choice. As a result, the offspring mated with members of their own lineage, strengthening the development of the new species.

Researchers previously assumed that the formation of a new species takes a very long time, but in the Big Bird lineage it happened in just two generations, according to observations made by the Grants in the field in combination with the genetic studies.

All 18 species of Darwin’s finches derived from a single ancestral species that colonized the Galápagos about one to two million years ago. The finches have since diversified into different species, and changes in beak shape and size have allowed different species to utilize different food sources on the Galápagos. A critical requirement for speciation to occur through hybridization of two distinct species is that the new lineage must be ecologically competitive — that is, good at competing for food and other resources with the other species — and this has been the case for the Big Bird lineage.

"It is very striking that when we compare the size and shape of the Big Bird beaks with the beak morphologies of the other three species inhabiting Daphne Major, the Big Birds occupy their own niche in the beak morphology space," said Sangeet Lamichhaney, a postdoctoral fellow at Harvard University and the first author on the study. "Thus, the combination of gene variants contributed from the two interbreeding species in combination with natural selection led to the evolution of a beak morphology that was competitive and unique."

The definition of a species has traditionally included the inability to produce fully fertile progeny from interbreeding species, as is the case for the horse and the donkey, for example. However, in recent years it has become clear that some closely related species, which normally avoid breeding with each other, do indeed produce offspring that can pass genes to subsequent generations. The authors of the study have previously reported that there has been a considerable amount of gene flow among species of Darwin’s finches over the last several thousands of years.

One of the most striking aspects of this study is that hybridization between two distinct species led to the development of a new lineage that after only two generations behaved as any other species of Darwin’s finches, explained Leif Andersson, a professor at Uppsala University who is also affiliated with the Swedish University of Agricultural Sciences and Texas A&M University. "A naturalist who came to Daphne Major without knowing that this lineage arose very recently would have recognized this lineage as one of the four species on the island. This clearly demonstrates the value of long-running field studies," he said.

It is likely that new lineages like the Big Birds have originated many times during the evolution of Darwin’s finches, according to the authors. The majority of these lineages have gone extinct but some may have led to the evolution of contemporary species. "We have no indication about the long-term survival of the Big Bird lineage, but it has the potential to become a success, and it provides a beautiful example of one way in which speciation occurs," said Andersson. "Charles Darwin would have been excited to read this paper."

The study was supported by the Galápagos National Parks Service, the Charles Darwin Foundation, the National Science Foundation, the Knut and Alice Wallenberg Foundation, and the Swedish Research Council.

The study, "Rapid hybrid speciation in Darwin's finches," by Sangeet Lamichhaney, Fan Han, Matthew T. Webster, Leif Andersson, B. Rosemary Grant and Peter R. Grant, was published in the journal Science on Nov. 23.

Uppsala University contributed to the content of this press release.

Charles Darwin and his book 'The Origin of Species' will forever be linked with the Galapagos Islands.

Darwin's finches are considered to be the world’s fastest-evolving vertebrates. This is because their appearance and behavior quickly adapted to the closed and rapidly changing environment on the Galapagos Islands.

In addition to the unique fauna, the plants are just as interesting. In the highlands, there are trees that have evolved from daisies, covered in colorful mosses and lichens. In the lowlands there are many cacti that have adapted to the islands' climate that is hot during the day and cooler at night. 

The Galapagos Islands accidental discovery: How did it affect Darwin's thoughts 

During Charles Darwin's nearly five-year circumnavigation of the globe aboard HMS Beagle, he spent only five weeks on the Galapagos Islands. The year was 1835 and Darwin was 26 years old. His discoveries on the islands were paramount to the development of his Theory of Evolution by Natural Selection.

On the islands, Charles Darwin discovered several species of finches. Thanks to his close observations, he discovered that the different species of finches varied from island to island. Besides elaborating his thoughts on natural selection, this also helped him in his investigation on the evolutionary changes of the finches. 

Isabela Island formation by 6 volcanic explosions

Wolf volcano, Isabela Island Source: NASA/Wikimedia Commons

Isabela, which is located on the western edge of the archipelago near the Galapagos hotspot, is one of the youngest islands. The one million year-old island was formed by the merger of 6 shield volcanoes: Alcedo, Cerro Azul, Darwin, Ecuador, Sierra Negra, and Wolf.

With the exception of Ecuador, these volcanoes are still active. This makes the Galapagos Islands one of the most volcanically active places on planet Earth. Volcan Ecuador and Volcan Wolf (the island's highest point with an elevation of 1,707 meters (5,600 feet), lie directly on the Equator.

The Isabela island provides excellent examples of a geologic occurrence that created the Galapagos Islands, including uplifts at Urvina Bay and the Bolivar Channel, tuff cones at Tagus Cove, and Pulmace on Alcedo and Sierra Negra, one of the most active volcanoes in the world.

Galapagos Islands: UNESCO World Heritage 

 Galapagos Islands (Ecuador) Source: Francesco Bandarin, UNESCO

The Galapagos Islands are situated in the Pacific Ocean about 1,000 km from the Ecuador. The archipelago and its immense marine reserve is known as the unique living museum and showcase of evolution.

For this, the Galapagos Islands are part of the UNESCO's World Cultural and Natural Heritage, therefore, the islands and their species are actively protected from any threat, including human threat. 

Charles Darwin Research Station 

Charles Darwin Research Station Source: Waltermera182/Wikimedia Commons

A trip to the Galapagos Islands is not complete without a stop at the Charles Darwin Research Station. Located in Puerto Ayora, Santa Cruz Island, the research facility is the operative branch of the Charles Darwin Foundation (CDF). It houses an extensive collection of preserved specimens of the Galapagos Islands' plant life. 

Fernandina Island: Home of first living marine iguana

Charles Darwin was amazed by the number of marine iguanas that foraged underwater. He thought that the iguana fed of fish and little animals. However, a dissection of a marine iguana led to the discovery that they feed off algae.

Fernandina Island Source: putneymark/Wikimedia Commons

Galapagos marine iguanas are pretty unique. They are the only modern lizards that can forage in the sea. They adapted to survive the scarce food on the Galapagos Islands. The marine iguanas scrape algae off rocks in the intertidal zone. Their flat faces help them gobble up more algae with each bite. 

 

Using their large sharp claws, the marine iguanas grip the rocky seafloor, so that the waves do not thrash them about. They are quite colorful animals. Although they are mostly black, on some islands they can also be spotted with a bit of red or blue. 

Galapagos land iguanas: threatened 

Relatives to the marine iguanas, the land iguanas on the Galapagos Islands are threatened to be extinct. By 1976, there were fewer than 100 left. The two endemic species of iguanas are among the largest in the world and unique to the Galapagos: they don't exist anywhere else on planet Earth. They are extremely vulnerable to human activity, which can cause their extinction. 

Charles Darwin Research Station Source: David Adam Kess/Wikimedia Commons

Charles Darwin & the Galapagos Islands 

Charles Darwin realized that the different islands that make up the archipelago were home to similar but different species. However, the unique creatures were perfectly adapted to their environments. This led him to ponder the origin of the inhabitants of these islands. 

When setting off from England in 1831, Charles Darwin was ready for a five-year voyage around the world with little ambitions for groundbreaking scientific research. However, after surveying the coasts of South America, the ship stopped over in the Galapagos Islands. This changed everything forever. 

Among those species that struck Charles Darwin so greatly were the finches, birds which are now named in his honor. Charles Darwin first supposed that these finches were all descendants of the same lineage.

But years later in 1859, Darwin finally consolidated all of his observations into his famous book On The Origin of Species. His book controversially altered the scientific view on the biological origins of life.

Charles Darwin and the HMS Beagle were on the Galapagos Islands during September and October of 1835. During five weeks, he had the opportunity to explore the islands and collect several Galapagos species which he used in his own research and that of his friends back in England.

Lonesome George

On June 24, 2012, Lonesome George was found dead by members of the Galapagos National Park Service. He was the sole remaining Pinta Island tortoise and a Galapagos conservation icon. The death of Lonesome George marked the extinction of the Pinta species of tortoise.

 “Whatever happens to this single animal, let him always remind us that the fate of all living things on Earth is in human hands.” — These words are inscribed on the information panel outside the enclosure of Lonesome George at CDRS/GNP.

In 1959, fishermen released three goats on Pinta Island. The fishermen wanted fresh meat on their fishing voyages. However, the tiny goat population exploded. By 1970, it was estimated to be around 40,000.

The goats devastated the vegetation, food for most local species. The goats had essentially eliminated any good tortoise habitat left and with it, all the remaining Pinta tortoises.

Lonesome George was the last of its species. 

Darwin’s tortoise - Harriet

Darwin's Tortoise Harriet Source: Thuresson/Wikimedia Commons 

Harriet was a Galapagos tortoise who had an estimated age of 175 years. She was born approximately in 1830 on the Galapagos Islands and was collected by Charles Darwin.

At the time of her death on June 23, 2006, she was a resident in Beerwah, Australia. She belonged to the Chelonoidis nigra species.

Harriet died of heart failure following a short illness. Harriet was the third oldest tortoise.

Tu'i Malila died in 1965 at the age of 188, and Adwaita died in 2006 at the estimated age of 255.

Galapagos penguin: endangered

The Galapagos penguin is on the endangered species list. It's a penguin endemic to the Galápagos Islands and the only penguin that lives north of the Equator.

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The Galapagos penguin can survive due to the cool temperatures resulting from the Humboldt Current and cool waters from great depths brought up by the Cromwell Current. Climate change is currently threatening the Galapagos penguin. 

Penguins are also threatened by pollution, bycatch, and by species introduced by humans that carry diseases that can spread to penguins as well. Cats pose a threat as predators.

Past strong storms such as El Niño have caused mortalities of up to 77 percent of the population of penguins, with dramatic declines of prey species and reduced breeding success.

Sea lions are leaving the Galapagos Islands due to climate change

Both tourism and climate change represent major threats for species found on the Galapagos Islands that don't exist anywhere else on the planet. According to WWF, sea lions are endangered. 

Species that have been introduced by humans such as dogs, carry diseases that can spread to sea lions. Sea lions on the Galapagos Islands are vulnerable to the effects of climate change on ocean currents, which impacts their fish prey abundance. They are also victims of bycatch in fisheries.

Galapagos baby sea lion Source: CharlesJSharp/Wikimedia Commons

Sea lions are leaving the Galapagos Islands to go to better suited waters for them close to Peru in a move adapting to climate change. The conditions of the sea around Piura are now similar to the Galapagos.

The sea lions are moving to Peru's Foca Island, where the waters have risen in temperature over the past years from an average of 17C to 23C, which is similar to the waters of Galapagos, which have become a favorite destination of tourists and botanists who look for their unique ecosystem and reputation as a living laboratory of evolution. However, they are forcing sea lions to search for a new home. 

Galapagos Islands: Land of extinct species 

Charles Darwin used to record his journeys in his journal. He wrote about the places, species he encountered, and his observations and thoughts about them. In occasions, he remarked that the convicts regularly ate tortoises.