How species are formed and how species remain separate are crucial questions in evolutionary biology. The offspring of crosses between different animal species are often infertile or die when still in the womb. A mule, for example, cannot reproduce. A sheep-goat hybrid, the result of a cross between a sheep and a goat, is usually stillborn. Such hybrids can also be dysfunctional, for example, because the sounds they make are a mixture of sounds from both parent species.
Remarkably, the offspring resulting from a cross between the ring-necked dove and the vinaceous dove, the two species studied by Den Hartog, are able to function and reproduce. Although the hybrid doves make a different sound to their parents, this sound is still functional.
By coincidence, biologists discovered the existence of a hybrid dove alongside the ring-necked dove and the vinaceous dove in a region of Uganda. The DNA of the hybrid dove has genes from both parental species. In order to mate, a male dove must defend his territory and attract females. This is why he coos. The coos of the ring-necked dove and the vinaceous dove are different and the hybrids have their own coo as well.
Den Hartog investigated the role of cooing in the process of species formation and hybridisation. She wanted to do this by determining the degree to which male doves of different species react to the coos of their own species, to those of the other species and to the coos of the hybrids. To this end she recorded the coos of the different species of males (for examples see fragments below) and subsequently played these recordings in the wild.
The researcher placed loudspeakers in the territory of a male dove to measure the response of the dove to other doves' coos. On hearing a male from his own species cooing in his territory, a male dove will usually approach the intruder and attempt to chase him away, cooing as he does so. This sometimes leads
|Contact: Paula den Hartog|
Netherlands Organization for Scientific Research