Tracing the evolutionary history of modified feathers and aerial displays.
The evolution of bird song has received a lot of attention (see for example this blog post), but some birds produce sounds in drastically different ways. Some Doradito species of genus Pseudocolopteryx, for example, generate mechanical wing sounds due to structural modifications on their feathers. Modified primary feathers have been described in three species: the Crested Doradito (P. sclateri), the Subtropical Doradito (P. acutipennis), and the Dinelli’s Doradito (P. dinelliana). The remaining two species in this genus – the Warbling Doradito (P. flaviventris) and the Ticking Doradito (P. citreola) – lack this feature. In addition, males in all species with modified feathers also perform aerial displays, indicating that these traits probably coevolved. As an evolutionary biologist, I cannot help but ponder how these feather modifications and aerial displays originated. Did they arise once or did each species independently alter its feathers? To answer this question, we need a solid phylogenetic framework. Once we know how these five species are related to each other, we can explore the evolutionary history of particular traits. A recent study in the journal Zoological Scripta provided the first steps in our quest to understand the evolution of mechanical sounds in these songbirds.
Emilio Jordan and his colleagues obtained genetic data for 37 individuals, representing all five species. Analyses of two mitochondrial (COI and ND2) and two nuclear (MYO and OCD) markers recovered a clear phylogeny in which the “non-mechanical species” are embedded within the three species that produce mechanical sounds with their modified feathers. This phylogenetic arrangement suggests that modified primary feathers (and the aerial displays) evolved in the common ancestor of all Doraditos and were consequently lost in the Warbling Doradito and the Ticking Doradito.
When we take a closer look at the modified feathers, however, the situation becomes less clear. Although three species produce mechanical sounds with their feathers, the structural modifications to their plumage are quite different. In the Crested Doradito and the Dinelli’s Doradito, the sixth and seventh primary feather are miniaturized, whereas the Subtropical Doradito has modifications on the third to seventh primary feathers. It is thus possible that these modified feathers have distinct evolutionary origins. In addition, the evolutionary history of the four molecular markers might not correspond to the evolutionary trajectory of the trait. Certain traits do not follow the species tree due to incomplete lineage sorting (as shown in marsupials) or introgressive hybridization. It might thus be necessary to unravel the genetic basis of the modified feathers and estimate phylogenetic trees for the underlying genes. Will they follow the species tree or not? In the end, the evolution of this trait might be more complicated than we expected.
Jordan, E. A., Tello, J. G., Benitez Saldivar, M. J., & Areta, J. I. (2021). Molecular phylogenetics of Doraditos (Aves, Pseudocolopteryx): Evolution of cryptic species, vocal and mechanical sounds. Zoologica Scripta, 50(2), 173-192.
Featured image: Warbling Doradito (Pseudocolopteryx flaviventris) © Dominic Sherony | Wikimedia Commons