36 years ago the arrival of an unknown bird to a remote island in the Galapagos archipelago had provided direct genetic evidence of a novel way in which new species arise. During this week’s issue of the journal Science, researchers from Princeton University and Uppsala University in Sweden reported that the newcomer is referring to one species mated with a member of different species resident on the island, giving origin to a distinct species that today consists of approximately 30 individuals. This study comes from work carried on Darwin’s finches, which live on the Galapagos Islands in the Pacific Ocean. The remote location has allowed researchers to investigate the evolution of biodiversity due to natural selection.
The investigation of the origin of this new species transpired during fieldwork conducted out over the last four decades by two scientists from Princeton, on the small island of Daphne Major. B. Rosemary and Peter Grant. B. Rosemary Grant said that the novelty of this study is that we can follow the emergence of new species in the wild. Within our work on Daphne Major, we were capable of recognizing the pairing up of two birds from various species and then watch what appeared to see how speciation occurred. In 1981, a graduate student working with the Grants on Daphne Major mentioned the stranger, a male that sang an unfamiliar song and was much more extensive in body and beak size than the three resident species of birds on the island.
Peter Grant stated that we didn’t see him fly in from over the sea, but we saw him shortly after he arrived. He was so diverse from the other birds that we knew he did not hatch from an egg on Daphne Major. The scientists took a blood sample and freed the bird, which next bred with a resident medium ground finch of the species Geospiz fortis, establishing a new lineage. The Grants and their research team followed the original Big Bird lineage for six generations, taking blood samples for use in the genetic investigation.
In the recent study, researchers from Uppsala University analysed DNA obtained from the parent birds and their child over the years. The researchers determined that the original male sire was a large cactus finch of the species Geospiza conirostris from Española island, which is more than 100 kilometres to the southeast of the archipelago. The striking distance meant that the male finch was not able to return home to mate with a member of his species and so chose a mate from amongst the three species already on Daphne Major. This generative isolation is considered a crucial step in the development of a new species when two separate species interbreed.
The baby was also reproductively isolated because of their song, which is used to entice mates, was unusual and failed to invite females from the resident species. The offspring also differed from the resident species in beak size and shape, which is an essential signal for mate choice. As a consequence, the family mated with members of their family, strengthening the development of the new species. Researchers earlier assumed that the creation of a new species takes a very long time, but in the Big Bird lineage, it occurred in merely two generations, according to investigations made by the Grants in the field in order with the genetic studies.
All 18 species of Darwin’s finches originated from a single ancestral species that established the Galápagos about two million years ago. The finches have since varied into different species, and changes in beak shape and size have allowed different species to use various food sources on the Galápagos. A significant requirement for speciation to occur through hybridization of two different species is that the new family must be ecologically contentious that is, good at fighting for food and other resources with the other species and this has been the case for the Big Bird lineage. Sangeet Lamichhaney, a postdoctoral fellow at Harvard University and the first author on the study said that It was shocking that when we compared the size and shape of the Big Bird beaks with the beak morphologies of the other three classes residing Daphne Major, the Big Birds occupy their niche in the beak morphology space. Thus, the succession of gene variants contributed from the two interbreeding species in combination with natural selection let to the evolution of a beak morphology that was competitive and different. The definition of this species has traditionally included the inability to give fully fertile progeny to interbreeding species. Though, in current years it has become clear that some closely related species, which avoid breeding with each other, do inevitably produce offspring that can pass genes to succeeding generations. The authors of the study have earlier stated that there has been a goodly amount of gene flow amongst species of Darwin’s finches over the last thousands of years.
Leif Andersson, a professor at Uppsala University, explained that one of the fascinating aspects of this study is that hybridization between two different species driven to the development of a new family that after only two generations behaved like any other species of Darwin’s finches. He continued that a naturalist who came to Daphne Major without knowing that this lineage originated very recently would have recognized this genealogy as one of the four species on the island. This confirms the value of long-running field studies.
According to the authors, it is likely that new genealogies like the Big Birds have dawned many times through the evolution of Darwin’s finches. The majority of these families have gone extinct, but some may have led to the development of contemporary species. Andersson said that we have no evidence about the long-term endurance of the Big Bird lineage, but it has the potential to become a success, and it also gives an excellent example of one way in which speciation occurs.