Author(s): Julia A. Clarke
Genomic mechanisms for the evolution of flightlessness in steamer ducks
We can gain insights into evolution by studying the sequence in which new features are acquired. But studying loss of features has its benefits, too. When a certain trait is lost multiple times in distinct groups of organisms, powerful statistical approaches can identify its genomic underpinnings. https://doi.org/10.1111/evo.13758 in Evolution 1 sheds light on the genetic changes associated with a loss of flight in birds. They compare the whole genomes of 59 individual steamer ducks (of the genus Tachyeres ) to examine loss of flight as it is evolving.
Steamer ducks occupy coastal habitats and lakes in southern Chile, southern Argentina and the Falkland Islands2 . They show a distinctive escape behaviour called steaming -- rapid, synchronized paddling of their wings and feet across water that mimics the action of their namesake, paddle-steaming boats (Fig. 1). Of the four recognized species, three (T. brachypterus , T. pteneres and T. leucocephalus ) are characterized by their inability to fly2 . Some heavier, male ducks of the usually flighted species, T. patachonicus , are also unable to fly, because their wing loading (the ratio of body weight to wing surface area) is higher than that of their lighter counterparts.
Figure 1 | Steaming behaviour in a steamer duck. Flighted and flightless steamer ducks in the genus Tachyeres show a distinctive escape behaviour called steaming, in which they paddle their feet and short wings rapidly across the water. Campagna et al. 1 sequenced the genomes of individual steamer ducks from each of the Tachyeres species (including the flightless Tachyeres brachypterus pictured here), and analysed them together with the birds' wing measurements to propose changes in gene expression that might underpin the evolution of flightlessness.
Credit: Bill Coster/FLPA
Falkland Flightless Steamerduck 'steaming' on water
All steamer ducks also walk proficiently on land, and dive to feed and to escape predators. Unlike puffins and penguins, which use wing movements in foraging and feeding, they do not steam to acquire food. However, they do use their wings when diving underwater, and the flight muscles in flightless species are only slightly proportionally smaller relative to body mass than in steamer ducks that can fly2 .
It has been debated whether the flightless species of steamer duck each independently lost the ability to fly or...