African indigobirds mate and then lay their eggs in the nests of firefinches, where the young hatchlings learn the songs of their adoptive parents. Male indigobirds later sing these songs as part of their courtship rituals, and this behavior leads to the development of new indigobird species, according to recent research by Michael Sorenson, an assistant professor of biology.
In earlier experiments Sorenson’s colleague, Robert Payne of the University of Michigan, Ann Arbor, showed that when indigobird eggs were transplanted from the nests of firefinches to another finch species, the chicks learned the song of the new species. When ready to lay their eggs, the female indigobirds laid them in the nests of the new species — the one in which they had hatched, not the species that their parents had parasitized.
 |
The new studies by Sorenson, Krishna Secf, a postdoctoral student who worked with Sorenson on the research, and Payne indicate that certain gene sequences are more common in some species of indigobirds than others, suggesting that interbreeding is rare. They attribute this to females having a preference for males singing a familiar song. A characteristic pattern of spots around the mouths of firefinch chicks helps the parent finches recognize their young. Since indigobird chicks with the same markings are more likely to survive in the host nests, the researchers believe that female indigobirds use the song to find mates with genes that will produce chicks with markings that help them best blend in with the finch chicks.
According to Sorenson and Payne, the adopted melodies and the pressure to produce chicks that will survive in the hosts’ nests contribute to the rapid evolution of a new species of indigobirds, even within the same habitat. It is the only example of sympatric speciation — the development of a new species within the same geographic area — found thus far among birds.
This research was reported in the journal Nature.
Figure: Examples of morphological variation between indigobird species. Nestling mouth markings in V. camerunensis (a) and V. chalybeata (b) mimic the young of their firefinch hosts, L. rara and L. senegala , respectively. Dark wing and plumage in V. chalybeata from West Africa (c). Pale wing and green plumage in V. raricola (d). White bill and blue plumage in V. camerunensis (e). Red bill and orange feet in V. chalybeata from southern Africa (f). |
