An international team of scientists concluded that the loss of flight ability in the Galapagos cormorant is associated with defective coding of proteins that regulate the growth of primary cilia.
Cormorants (Phalacrocorax) are a genus of waterfowl that are widespread in coastal areas. Phalacrocorax includes about 40 species, only one of which, the Galapagos cormorant (Phalacrocorax harrisi), is unable to fly. Morphologically, the latter is distinguished by shorter wings and a flat chest. At the same time, unlike other flightless birds, such as ratites and penguins, the Galapagos cormorant lost its ability to fly relatively recently - about two million years ago versus 50 million years. Therefore, using the example of P. harrisi, researchers have the opportunity to more accurately describe the process of leveling a significant evolutionary trait.
To find out the reasons for the loss of the ability to fly, researchers from the University of California at Los Angeles, the Southern University of Chile and other institutions conducted genome-wide sequencing of four species of cormorants: Biguan (Phalacrocorax brasilianus), eared (Phalacrocorax auritus), Beringian (Phalacrocorax pelag). To identify mutations that influenced the loss of the trait, the authors studied the DNA of these taxa and built a phylogenetic tree. The results showed that in the course of evolution in the genome of P. harrisi, mutations appeared in the genes Evc, Ift122, Ofd1, and Wdr34, encoding proteins that regulate the work of cilia - intracellular organelles.
Comparison of the wing length of the eared (left) and Galapagos cormorants (right) / © A. Burga et al., Science, 2017
In most eukaryotes, cilia act as a sensitive antenna that modulates intracellular signaling pathways. In the case of humans, mutations in the genes responsible for the functioning of cilia can lead to diseases from the group of ciliopathies, which are expressed, among other things, in skeletal system abnormalities - a decrease in the length of the ribs and arms. In addition, as part of the work, scientists discovered a mutation in CUX1 - this gene regulates the production of proteins that mediate the growth of cilia. Interestingly, CUX1 is conserved in mammals and birds: for example, in chickens, it determines the development of limbs. Thus, the mechanism may also lie in the loss of the ability to fly by cormorants.
The Galapagos cormorant is the largest member of the genus. With a mass of 2.5–5 kilograms and a body length of 90–100 centimeters, it has wings that are about three times smaller than what is needed for flight. According to scientists, the loss of a trait could occur in the absence of the need to migrate. Now P. harrisi lives on the islands of Isabella and Fernandine, where it has almost no natural enemies and is provided with food. At the same time, the reduction of the wings could increase the efficiency of hunting: due to the decrease in buoyancy, the Galapagos cormorant is easier to dive under water. The authors note that the described approach can be applied to other cases of variation between closely related species.
The article was published in the journal Science.
Earlier, researchers showed for the first time that waterfowl actively use their hearing underwater.