“Sparrows” still came from “falcons”

Well, as good as. The passerines, named after the Latin for sparrow, include over 50% of bird species, and in 2008 Hackett et al’s (1) landmark genetic study suggested they were most closely related to parrots but also close to falcons (See GrrlScientist’s posting for details ).

Wouldn’t you have expected falcons to be closer to, well, hawks, say? That’s not what it seems like now.

Don’t worry – they’re so close they’re in the same group, and the main message from this posting is that it seems likely they are all part of a basically (or basally) “birds of prey” group. (This explains the most and has no contrary evidence.) It’s widely known as the Land Birds group because it contains so many other land birds, but think of it as having an ancestral bird of prey at its root, and all the bizarrenesses magically disappear. The line leading to hawks does seem to have split from that leading to falcons rather a long time ago, but their last common ancestor will already have been a bird of prey. Owls and other raptors split off at earlier points but most plausibly still from birds of prey. Having the trunk of a family tree occupied by predators, with other types evolving as branches, is not uncommon to say the least.


Last Tuesday it happened again. Suh et al. (2) got passerines, parrots and falcons in the same relationship using different DNA: retroposon insertions, which as you no doubt know are virtually homoplasy-free 😉 . I didn’t but it wouldn’t surprise me. But even ordinary genes are a few steps removed from the physicalities evolution commonly acts on. If one set of genes causes a physicality, a different set may well reverse it, leaving the genetic evidence unerased and still available. Also the same physicality evolving on two different occasions may be caused by two different gene changes, which the genetic tree will be able to distinguish. This again makes the genes’ messages clearer; but when the family trees (phylogenies) are generated using the physicalities themselves, they are more often confused by homoplasy (parallelisms) or reversals. Reasonable evolutionary biologists would usually guess this the moment they thought about it but many palaeontologists were, and some still are, convinced morphology is at least as good as molecules if not better. Unfortunately, although molecules may be a better bet in the long run, they have also been quite fickle as Suh et al. remind us, which is why their paper’s choice of especially reliable molecules is so welcome (or would be if they are, but see Sobielski, who asks an interesting question of the paper’s selectivity in procedural terms, as well as the molecules’ infallibility).

Incomplete Lineage Sorting: To help make their trees, Suh et al. use retroposons, but surprisingly these can still give unclear results. (Image from The Secret Dinobird Story.)

Incomplete Lineage Sorting:
To help make their trees, Suh et al. use retroposons, but surprisingly these can still give unclear results.
(Image from The Secret Dinobird Story.)


So those annoyed in 2008 about passerines being close to falcons were annoyed all over again on Tuesday. Remember, the new study used a different gene dataset, meaning a big coincidence if the similar results were caused by something other than the true relationships – a coincidence inviting explanation by anyone disbelieving the relationship; but those disbelieving the relationship are not the types to appreciate the need for the explanation.

Of course, at the moment when ‘sparrows split from falcons’, the two new lines would have been as good as indistinguishable from each other and not necessarily close to falcons or sparrows or parrots. But Suh et al. suggest (convincingly) that no other landbirds but those two left the falcons at this point. Splitting off just before them but still on the “falcon side” was the Seriemas lineage – long-legged rather predatory birds from South America which may have been related to the legendary phorusrhacid giant flightless predators. On the “hawk side” of the landbirds group, many other non-“birds of prey” split off including woodpeckers and kingfishers. The first, possibly even before any modern birds of prey, seem to have been the mousebirds which coincidentally look to me like a cross between a sparrow and a kestrel. Certain passerines such as sparrows themselves have evolved in parallel to occupy similar niches, and have been pushing the once flourishing mousebirds towards extinction.

Speckled mousebird (Wikipedia)

Those wonderful retroposon genes were occasionally caught out a bit, the paper noted, further evidence that the major radiation of birds (after fowl had already departed, and before them ratites – flying at that time) was initially very rapid. It would be astonishing if this were not due to a post-Cretaceous recovery. Suh et al. however place the major radiation before the end of the Cretaceous, which then has no apparent effect on the traceable evolution. Unbelievable. They presumably have arguments based on palaeontological events for their timescale, but why the end of the Cretaceous wasn’t considered a landmark palaeontological event, or why accelerated genetic variation in the radiation wasn’t considered, I don’t know.

I also wish they hadn’t described their work as a “robust phylogenetic framework”. It inevitably incorporates both hopeful judgements, and p (probabilistic) values for the statistical operations, so roping in the term “robust” is at best pretentious, no matter how good the work is. But it is pretty good as far as I can judge at the moment. They take the opportunity to claim the similarly well-developed vocal skills of parrots and passerines as corroboration for their tree. (Consilience: explanation of something extra the theory wasn’t designed to explain.) Passerines include such vocal specialists as mynah birds which are a type of starling, and lyrebirds.

House sparrows

(1) Shannon J. Hackett et al. (2008-06-07). “A Phylogenomic Study of Birds Reveals Their Evolutionary History”. Science 320 (5884): 1763–1768.

(2) Alexander Suh et al. (2011-08-23). “Mesozoic retroposons reveal parrots as the closest living relatives of passerine birds”. Nature Communications 2.

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One Response to “Sparrows” still came from “falcons”

  1. Alex says:

    Hi,

    thank you for the nice post and nice tree! 🙂

    By the way, a reply to Sobielski’s doubts can be found here:
    http://dml.cmnh.org/2011Sep/msg00004.html

    All the best,
    Alex

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