No, The Same Flightless Bird Species Didn’t Evolve Again – But the Niche Was Filled Again

Yes, sure, allowances for having to fit a complex scientific idea into a short newspaper article for those who are not – let us say – among the intellectual giants of our civilisation. But you here can have it straight, right?

BACK FROM THE DEAD ‘Extinct’ bird species reappeared on Indian Ocean island after 30,000-year gap, Brit researchers discover
The flightless white-throated rail seemed to go extinct then bizarrely reappeared

No, that’s not what happened.

A flightless bird that became extinct when its home island became flooded by the sea has been brought back to life. Scientists said the astonishing resurrection of the bird, a type of rail, occurred due to a rare process called iterative evolution.

It might be called iterative evolution but that’s more than a little misleading.

Rails are a family of flying birds you might see skulking around marshes, and some rail species are known for dispersing quite far from their initial homes. It’s not so surprising that the white-throated rail species colonized a distant island—but a new paper documents perhaps the first case of the same genus of rail colonizing the same island and then evolving along the same trajectory in response. “In 20,000 years or less, the rails were evolving flightlessness again,” Julian Hume from the Natural History Museum in the United Kingdom told Gizmodo. “Evolution can be incredibly quick if the conditions are right.”

That is better. The full paper is here.

The Aldabra rail, Dryolimnas cuvieri subsp. aldabranus, endemic to the Aldabra Atoll, Seychelles, is the last surviving flightless bird in the Indian Ocean. Aldabra has undergone at least one major, total inundation event during an Upper Pleistocene (Tarantian age) sea-level high-stand, resulting in the loss of all terrestrial fauna. A flightless Dryolimnas has been identified from two temporally separated Aldabran fossil localities, deposited before and after the inundation event, providing irrefutable evidence that a member of Rallidae colonized the atoll, most likely from Madagascar, and became flightless independently on each occasion. Fossil evidence presented here is unique for Rallidae and epitomizes the ability of birds from this clade to successfully colonize isolated islands and evolve flightlessness on multiple occasions.

It’s not, absolutely not, the same species.

So, to explain what really happened. And happens. Not scientifically, but in that story shape that fits into human brains. There are ecological niches out there. Spaces into which a sustainable pattern of life can squeeze itself. The usual determinant of that shape is all the other animals and beasties there are around. When you’ve an island with few to no predators then that will indeed suit being a small walking animal. Or being a small walking animal will be sustainable over the generations without everyone getting eaten say.

A place without the sort of predators that eat small walking animals is also likely to be the sort of place that doesn’t have small walking animals. So, some members of a species that get there might well, over time, evolve into small walking animals. ‘Coz there’s no one around to eat them, see? And given flight it’s likely to be birds that do get there. As with the Dodo. As with New Zealand really, where birds ended up being most of the fauna. Occupying niches which elsewhere are inhabited by mammals perhaps.

Actually, given time, we’d expect the evolution to take place to fill the niche.

Worth noting how this works too. In any generation of birds some of the kids won’t be able to fly. In most places at most times this means they get eaten. Or can’t hunt, or feed, or summat. In a place with no predators of small walking things then some might survive. Enough to start having their own kids which can’t fly and so on. The evolution here is the not death of the divergences.

This isn’t the same species re-evolving. Rather, it’s evolution filling the same hole in the ecology. This is rather closer to convergent evolution – the Tasman tiger and the wolf are wildly far apart in evolutionary terms but their jaws look remarkably similar. Because there’s a niche in most ecologies for the sort of beastie that crunches up the small walking animals….

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