Researchers have found new evidence about what made some of New Zealand’s iconic birds flightless.
The study, published today in Science, examined the genomes of eight flightless ratites, including great and little spotted kiwi, Okarito kiwi and the extinct little bush moa. They suggest the switch to flightlessness came from non-coding DNA that regulates protein genes, rather than from the protein-coding genes themselves.
University of Otago’s Dr Paul Gardner, a co-author on the paper, said their study “tells us more about the origins of moa and kiwi”. “It supports the hypothesis that the ancestral moa flew here, while the ancestral kiwi, which is related to the emu may have walked, or indeed flown from the likes of Australia or Madagascar over the ancient Gondwanan continent.”
The SMC gathered comment from experts not involved with the research.
Dr Gillian Gibb, Massey University, comments:
“We’ve long suspected the drivers of flightlessness in birds lies in their non-coding DNA, rather than changes in the DNA sequences that make proteins. We still know very little about these non-coding regions and their role in rapid morphological change. Here Sackton and colleagues have looked at the role of non-coding DNA in the repeated loss of flight amongst the palaeognaths. Palaeognaths include many of the iconic flightless bird species such as kiwi and ostriches.
“When you have a case of repeated trait evolution (in this case loss of flight) an important question is if the same genes or genomic regions are involved each time it happens, or if each case might represent a novel pathway to flightlessness. Sackton and colleagues have been able to show that loss of flight is strongly associated with certain conserved noncoding elements (called CNEEs) that show convergent evolutionary acceleration.
“The strength of this study is the number of palaeognath genomes that have been sequenced. This detailed comparative genomic approach has identified these non-coding regions. In this fast-moving field, I am sure we will see more studies of this sort in the future, allowing us to gain greater insight into genome functioning.
“From a New Zealand perspective, this study publishes the first complete genomes of three more kiwi species and that of an extinct moa. It is great that there are New Zealand scientists involved in this international research collaboration, and these published genomes will be a valuable future resource for all researchers.”
Conflict of interest statement: I also work in the field of flightless evolution research using avian comparative genomics.
Dr Nic Rawlence, director, Otago Palaeogenetics Laboratory, University of Otago, comments:
“The evolution and loss of flight in ratites, including the extinct moa and endangered kiwi, has long fascinated evolutionary biologists. The members of this bird group are descended from flying ancestors that independently lost flight after the extinction of the dinosaurs. Moa are unique among ratites in that they had no wings left. However, the partial moa genome contains most of the functional genes associated with wing development and flight, creating an evolutionary mystery. This lack of wings is not a simple case of gene loss. Now Sackton et al., including fellow kiwi Paul Gardner, with the support of Ngai Tahu and Te Ati Awa, may have the answer.
“Sackton et al. compared ratite genomes, including several new kiwi genomes and the newly sequenced moa genome. Rather than flightlessness in ratites being explained by independent loss or loss of function of the same suite of genes (i.e. convergent evolution), it looks like the same suite of non-coding regulatory elements in the genomes are to blame. These are genetic regions that do not code for proteins, instead controlling their levels of production. Not only that, these regulatory elements are closely associated with the developmental pathways that allow flight, like wing development.
“Sackton et al. have gone a long way to answering how these poster birds for evolution became flightless, and why the moa lost its wings. More ratite genomes, especially additional moa and the extinct Madagascan elephant bird, would go a long way to finally resolving this debate. As for the de-extinction of moa, this study just goes to show that having a genome does not mean you can bring back the dead – there’s a whole lot of regulation of that genome that you would also have to recreate as well. That’s a tough call.”
No conflict of interest.
Dr Michael Knapp, Department of Anatomy, University of Otago, comments:
“The study by Timothy Sackton et al. looks at the functional genomic basis of loss of flight in birds. As a model system, they use a group of birds that is characterised by a high percentage of flightless species, the ratites. From a New Zealand perspective, that is a very interesting choice as the group contains some of our most iconic birds, including kiwi and moa.
“Within the group of ratites, the ability to fly has been lost at least three times independently, and the researchers ask whether these events are caused by similar processes in the genome of the birds losing their ability to fly.
“This is certainly not a new question, but previously, researchers looked for a similar process mainly among genes, i.e the parts of the genome that hold the instructions for producing the large variety of proteins that control different body functions.
“So, previously researchers would have for example asked: Are the same genes responsible for kiwi and moa losing their ability to fly, or is this caused by different genes in the different species? As genes control the production of proteins and proteins can directly affect developmental process like the formation of flight muscles, genes are an obvious place to start looking for changes that cause a loss of flight.
“In contrast, this study found that while there are common processes underlying the loss of flight in kiwi and moa (and other ratites), the loss of flight is not so much caused by changes in genes, but by changes in regions that control the function of genes. These are parts of the genome which, for example, can switch a gene on and off.
“What it means is that the changes in the genome that underlie the loss of flight are not primarily controlled by genes, but by the genome regions that control the genes.
“The strength of the study is that it not only identifies potential mechanisms contributing to the loss of flight but also tests their effects in a living system, in this case, chicken tissue. These tests strengthen the findings, which are also in contrast to previous findings on flight loss in cormorants. In that case, genes were found to directly contribute to the loss of flight.
“It is, of course, difficult to say whether these results are conflicting, or whether they are simply owed to the fact that different groups of birds may lose their ability to fly in different ways. In the latter case, previous and present studies could simply be interpreted as showing a broad range of processes causing the loss of flight in different groups of birds.”
No conflict of interest