Redrawing Ratite Relationships

A group of international scientists partly sequenced the genome of two extinct birds: the moa (New Zealand) and the elephant bird (Madagascar). Evolutionary analyses of their DNA reveal some surprising relationships.

Try to channel your inner David Attenborough voice for a moment and imagine him creeping through the shrubbery somewhere in Madagascar: ‘‘this is an elephant bird. Unable to fly, she is, if not the tallest, almost certainly the heaviest bird that ever lived on Earth, weighing nearly half a ton. And she is about to lay an equally impressive ten-kilogram egg.’’ Sadly, this is but a poor fictional rendering of an encounter that never happened.

What a way to start a scientific paper! Compare this with the usual dull opening sentences in other evolutionary studies, such  ‘Incongruence between phylogenies generated by different sets of genetic and phenotypic data poses a significant challenge in evolutionary biology‘ or ‘Hybridization, the interbreeding of species, has always intrigued ornithologists.‘ Are you still paying attention after these sentences? (Actually, these two lines are the opening sentences of two of my own papers…).

The paragraph quoted above was written by Florian Maderspacher (Senior Reviews Editor at the scientific journal Current Biology). His article is a kind of commentary on another paper published in Current Biology. In this study, Takahiro Yonezawa and colleagues unraveled the evolutionary history of the ratites, a group of flightless birds that contain among others, ostrich, emu, rhea and kiwi.

The exciting feature of this work is the sequencing of two extinct ratites: the moa and the elephant bird. The researchers obtained DNA from fossil bones and compared the DNA of these two giants with their living relatives. This led to some surprising findings…

First, the moas appear to be closely related to tinamous, a family of cryptic birds that hide in the understory for the South-American rainforest. Second, the giant elephant birds (which could reach up to three meters) are the closest cousins of the small, round, furry kiwis.

Ratite.jpg
The family tree of the ratites. (From Maderspacher, 2017)

As often (well, all the time) happens in science, new insights lead to new questions. The position of the tinamous within the ratites, for example, raises an intriguing dilemma. All the ratites are flightless, while the tinamous do fly. Did tinamous re-evolve their ability to fly? Or did flightlessness evolve separately in the different members of the ratite radiation?

And what happened with the elephant birds and the kiwis. They are closely related but occur on islands (Madagascar and New Zealand) that lie thousands of kilometers apart and have never been close to each other in Earth’s history. So, how the hell did these birds end up on their respective islands?!

Food for thought. Mmm, kiwis…

kiwi

References

Maderspacher F (2017). Evolution: Flight of the Ratites. Current biology : CB, 27 (3) PMID: 28171755

Yonezawa T, Segawa T, Mori H, Campos PF, Hongoh Y, Endo H, Akiyoshi A, Kohno N, Nishida S, Wu J, Jin H, Adachi J, Kishino H, Kurokawa K, Nogi Y, Tanabe H, Mukoyama H, Yoshida K, Rasoamiaramanana A, Yamagishi S, Hayashi Y, Yoshida A, Koike H, Akishinonomiya F, Willerslev E, & Hasegawa M (2017). Phylogenomics and Morphology of Extinct Paleognaths Reveal the Origin and Evolution of the Ratites. Current biology : CB, 27 (1), 68-77 PMID: 27989673

The paper by Maderspacher also links to a clip by David Attenborough on moas. Enjoy!

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