P.Z. Myers on the Platypus

P.Z. Myers says that the platypus is a fine animal--it has just been pushed around by different evolutionary pressures over the past 160 million years than have modern mammals, reptiles, and birds. I say that the platypus is an otter gone horribly wrong:

Pharyngula: The platypus genome: Every organism is going to be a mix of conserved, primitive characters and evolutionary novelties — a mouse is just as "weird" as a platypus from an evolutionary perspective, since each is the product of processes that promote divergence from a common ancestor, and each are equidistant from that ancestor.... [M]odern echidnas, elephants, and emus are all products of different evolutionary trajectories through history, and no one by itself is a representative of the ancestral condition. We derive the ancestral state by comparison of multiple lineages... [this] adds another lineage to the [genomic] data set, one that diverged from ours over 160 million years ago. It is a lens that helps us see what novelties arose in that 160 million year window....

So what are the details that we've learned from the platypus? One important message is the unity of life. The platypus has about 18,000 genes; humans have 18-20,000 genes. Roughly 82% of the platypus genes are shared between monotremes, marsupials, eutherians, birds, and reptiles....

An interesting specialization in the platypus is the evolution of venoms. The platypus has small, sharp spurs on its hindlimbs that it uses to inject defensive poisons into predators, a very unusual feature not found in other mammals. Where did these venoms come from? As it turns out, by duplication of genes that have other functions, with subsequent divergence, and many of these genes also come from the innate immune system. In particular, there are a set of proteins called the β-defensins... the bullets of the immune system; they can bind to viral coat proteins, they can punch holes in bacterial membranes.... The platypus has repurposed these genes, making copies that have been selected for more effective toxicity when injected into other animals.

One very cool observation is that these are also the same proteins used in venomous reptiles... two distant relatives, the lepidosaurs and the monotremes, all use β-defensin derived venoms. Does this imply that their last common ancestor also used these venoms? No, and this is where the details are important. Venomous snakes and the platypus have different duplications of the β-defensin genes... these are independently derived features, not primitive at all... convergent evolution....

One virtue of the platypus is that it provides a relatively closely related outgroup to help tie together, and give perspective on, the various mammalian genome projects. It's all part of the big picture in defining what a mammal is...

Comments

[Bloix]

Only adult males have venomous spurs. All are born with non-venomous spurs but at about one year females lose their spurs while the males' spurs become venomous.

[Bloix]

Only adult males have venomous spurs. All are born with non-venomous spurs but at about one year females lose their spurs while the males' spurs become venomous.

[dennisS]

That's what I love about this site; the host puts up a platypost and right away experts chime in. Here's what I hope I learn in follow-on posts. How do defensive poisons work in this case? Like a toad? The next platypus gets away thanks to the hangover some predator had after his / her last platypus meal? Or, does it act fast enough to stop the predator from taking a second bite? Also, into which securities should I direct my discretionary income?

Ok, I'm just messing with you on the last question. I don't have any discretionary fundage.

[Colin Danby]

I just hope Larry Summers doesn't get hold of this bit about the spurs.

[Ronald Brak]

The venom is apparently wicked painful and morphine doesn't help. It is possible that the main purpose of the venom is for defending breeding grounds from other male platypi rather than self defence. Maybe Bloix knows more about this.

But personally, when I look at an otter, I can't help but feel sorry for the poor thing because it doesn't have a bill...

[Bloix]

There's a theory that the males use their spurs to defend territory from other males and the venom does become more potent during breeding season, but apparently no one knows for sure. Thttp://www.expasy.ch/spotlight/back_issues/sptlt029.shtml

[John Emerson]

The same arguments about the plural of "octopus" can be made about the "platypus". One PZ poster used "platypodes", which is a sort of Latin-Greek joke. Platypuses and platypi both would be more or less OK.

The ugly weird face of the star-nosed mole is splendidly functional:
http://www.livescience.com/imageoftheday/siod_050207.html

The naked mole rat is also weird looking, and it has developed ant- or termite-like social forms:
http://nationalzoo.si.edu/Publications/ZooGoer/2002/3/nakedmolerats.cfm

[John Emerson]

Just in from Carl Zimmer: How the platypus lost his stomach:

http://www.amazon.com/gp/blog/post/PLNK1NYIRGNRNMMKI

Zimmer is the only NYT reporter I can think of who seems better than expected, rather than worse. Newspaper science reporting has tended to be pretty bad even in the best of times, but everyone seems to like Zimmer.

[Colin Danby]

Zimmer rules. Read his book on parasites.

[P.M.Lawrence]

"All are born with non-venomous spurs..." - no, they aren't born at all, they hatch.

[Ian Whitchurch]

Platypus is proof not only of Six-Day Creation, but also that there was a party immediately between the end of day six and the Day of Rest.

Look, seriously, Occam's Razor says the best way to explain Platypus is a bunch of drunk archangels and a bits box. Crocodile skeleton ? Beaver Fur ? Duck Bill ? EWAR system out of a hammerhead shark ? Poison spur ? Milk but no nipples ?

Gotta be drunk archangels hitting the bits box.