A new species of finch has evolved in just two years in the Galapagos, and scientists were able to observe it happen in real time.
The new finch species in the Galapagos islands, which researchers have dubbed the "Big Bird" species.
Finches are famous for having helped Charles Darwin figure out his theory of evolution by natural selection. Darwin’s visit to the Galapagos islands led him to discover that the species of finches in the area--now called Darwin’s finches--vary from island to island. According to this study, two of the 18 species of Darwin’s finches merged to create a new one in a much shorter time that species are usually known to evolve.
A male large cactus finch (Geospiza conirostris) had likely flown to Daphne Major island, and Princeton biologists Peter and Rosemary Grant knew right away that the bird was an interloper. However, they witnessed it mate with two females of a species native to the island, the medium ground finch (Geospiza fortis).
Daphne Major is a tiny island north of the island of Santa Cruz, while Española island is to the southeast of Santa Cruz. [Image by Matthew Stevens]
Researchers determined that the male was from Española island, which was quite far from Daphne Major. Thus, he was likely unable to fly home to mate, and therefore had to mate with females from at least one of the three finch species endemic to Daphne Major. Scientists usually consider reproductive isolation to be a vital step in the the creation of a new species as a result of interbreeding.
Another thing that scientists knew--or at least thought they knew--about the evolution of a new species is that it takes a significant amount of time. However, these new finches in the Galapagos evolved into their own species in just two generations.
So how were the researchers able to figure out that what they were looking at was indeed a new species? For one thing, the birds of the new lineage were ecologically competitive, which meant that they were able good at competing with other species for resources. Researchers have also noted that the new lineage had a different beak size and shape compared to their predecessors, something that also meant that they can access different food sources.
A member of G. conirostris on Española island [Photo by Dusan M. Brinkhuizen]
The new lineage, which researchers dubbed the “Big Bird” species, was also genetically distinct. Researchers thought that the hybrid offspring would eventually grow to mate with the other species endemic to Daphne Major. However, the Big Bird finches mated exclusively with other, likely because the females of the Daphne Major species cannot recognize their songs. Finches usually attract mates through their songs, and since the new lineage’s songs were unusual, they weren’t able to attract the females of the island.
The fact that members of two different--but not that different--species can procreate is well known. After all, animals like donkeys and ligers (the offspring of a female tiger and a male lion) exist, proving that such matings can successfully reproduce. However, the hybrid offspring of two species usually cannot themselves reproduce, or have a hard time doing so.
That wasn’t the case with the new chicks that sprung from members of G. conirostris and G. fortis. When these chicks hatched, a new lineage began. They grew up isolated on Daphne Major, and when they matured, they had to find a mate among themselves.
A member of G. fortis [Photo by Peter R. Grant]
Amazingly, the Big Bird finches were quite resilient. There was drought on the island from 2002 to 2003, during the species’s fourth generation. All but two of the birds lived through that drought, coincidentally a male and a female who also happened to be brother and sister. These two mated and managed to produce 26 offspring.
"All but nine survived to breed - a son bred with his mother, a daughter with her father, and the rest of the offspring with each other - producing a terrifically inbred lineage," said Rosemary Grant.
Still, the species managed to survive. They were larger than any other finches on Daphne Major, with differently-shaped beaks to boot, which meant that they can access food sources that the other finches on the island cannot. Thus, without too much competition for food, the new species was able to pull through the drought and replenish its numbers. As of 2012, the Grants counted 23 individuals with a total of eight breeding pairs among them.
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