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Amused Muse

Inspiring dissent and debate and the love of dissonance

Thursday, November 09, 2006

Arms Races and Manipulation, Part II

If evolution can be viewed as a sort of “arms race,” one often assumes that if an animal manipulates another, the victim will, via random mutation and natural selection, develop counterstrategies to escalate the arms race rather than capitulate. However, Dawkins shows several examples of how this is not necessarily so.

For example, the foster parents of the cuckoo continue to feed their changeling “child” despite the obvious absurdity of a tiny Garden Warbler straining to feed a cuckoo several times its size. Why doesn’t the Warbler recognize this incongruity, when apparently some host parents of cuckoos can indeed recognize flaws in the cuckoo’s egg mimicry? Why does the host parent recognize the parasitic egg but not the more obvious parasitic changeling fledgling bird?

Dawkins’s answer is that natural selection does not act uniformly at all times in any animal’s life. Selective pressure may be stronger at some points in the life cycle than others, or natural selection may have no effect on evolution even if a beneficial mutation were to arise. As an example of the first case, Dawkins points out that recognition of a cuckoo egg in one’s nest gives the host parent the chance to gain an entire breeding cycle, whereas recognition of the incongruous fledgling would buy at most a few days, and that probably too late for the host parent to breed again. Moreover, the actions of the cuckoo, its exaggeratedly gaping mouth, its size, could indeed act as a “drug” on the foster parent, no less than the song of a male nightingale acts as a drug on the female reproductive cycle (and, incidentally, upon the poet’s imagination).

However, a fascinating example of how an animal’s victimhood can be perpetuated is exemplified by slave-making ants. Some species of ants spend a great deal of their time raiding the nests of others and carrying off the larvae and pupae, which subsequently hatch in the new nest and begin to labor for their “masters.” This is a disturbing and puzzling development. Why don’t the enslaved worker ant colonies develop a resistance to the strange environment, filled with others not their genetic sisters—for example, by evolving a genetic disposition to cease work (to go on “strike”) when in a strange queen’s lair?

Remember that worker ants do not reproduce. Therefore, any beneficial mutation that arose in the enslaved ants would not be passed on to the rest of their home nest. At any rate, the raids do not happen often enough to destroy the victims utterly, who are under little selective pressure to evolve complex adaptive countermeasures against slave-making behavior on the part of others that, while aggressive, does not threaten the existence of the nest. An uneven battle ensues, in which the slave-making ants can be said to win the war.

Dawkins indicates that this situation is not unlike the phenomenon of a certain species of hybrid frog, which has one set of chromosomes that is jettisoned in meiosis and one set that is passed on to its offspring. The set of chromosomes (dead-end replicators) that is jettisoned in the hybrid frog is perpetuated in the pure bred species that carries two sets of these chromosomes (which become germ-line, not dead-end, replicators in this species). Thus, any beneficial mutation in the dead-end replicator line will be passed on in the pure bred species that contains two sets of these chromosomes (because in this species these sets of chromosomes are not dead-end replicators), but will not be passed on in the hybrid species. The situation of the enslaved ants is like that of the hybrid species of frog: their genes have phenotypic effects and can even be selected, but they will not be transmitted in the hybrid species, and thus are irrelevant to that particular species' evolution.


Anonymous Anonymous said...

Hah, I never cease to be amazed at the complexity of varying levels of competition and cooperation in this neat little planet. All the more reason to save it and combat the forces of ignorance and superstitious rot that threaten it.
Here's raising my glass to giving the boot to Rummy.
Cheney and Rove...better put on your athletic cups, boys.

November 10, 2006 1:16 PM  
Blogger Kristine said...

Did you hear that President Ant Queen told Nancy Pelosi that he knew some great interior decorators for her new curtains for her office?

Pelosi should have said: "Appropriate, because I think it's curtains for you, too."

Thank you! Thank you! I'm here all week!

November 10, 2006 3:06 PM  
Anonymous Anonymous said...

I knew nothing about what Kristine mentioned in the post. I am a doctor, not a biologist, so I am excused. However, enlightening myself by reading this blog fills me with pleasure. From my ignorace, I have nothing else to add.

November 10, 2006 4:55 PM  
Blogger Kristine said...


You have lots to add. You posted an entry about speciation yourself.

As for me, I'm a secretary, not a biologist, either. What I'm saying in this series is my reworking of Dawkins' work. Taking notes while I read TEP is the best way for me to learn. Anyone can learn--that's my point.

Do you think that a little over a year ago, before I stumbled across the website Pharyngula, started blogging, and met people online like you, that I could have coined the term "polypepTard" for DaveScot and the UD gang? ;-)

November 10, 2006 5:30 PM  
Anonymous Anonymous said...

I think that just shows the corruptions that are available online.....


November 11, 2006 3:41 PM  
Blogger Kristine said...

Corruption of me, or by me...?

November 12, 2006 5:29 PM  
Blogger Rev. Barky said...

Some years ago I purchased an ant farm kit. I dug up a nest in the back yard and it included 3 queens. I kept the small colony for a few months. After a while there was a change in the ant-karma and over a period of a couple of weeks the worker ants dismembered each of the queens thereby sealing the fate of the colony. I waited for one of the worker ants to transform into a new queen, since I heard they can do that. It never happened. Why would they destroy themselves like that? I guess ants didn't evolve inside cheap plastic terrariums.

(note - saw Michael Newdow today - he was great!)

November 12, 2006 9:00 PM  
Blogger Unknown said...

Speaking of ants...

I've been reading The Ancestor's Tale. According to the Leaf Cutter's Tale, these ants have evolved farming and domesticated a certain species of fungus (the leaves they haul are not eaten, but rather used as compost to grow the fungus). There are also certain other species of ant that have domesticated and "milk" aphids of their nutritious honeydew.

Mmmm, aphid poop.

That's like the coolest thing ever. Evolution friggin' rawks.

November 12, 2006 11:11 PM  
Blogger Kristine said...

Why would they destroy themselves like that?

I guess that they don't know that they're destroying themselves, Rev. Though of course, the ants who act in this manner don't pass their queen-killing genes on.

Evolution friggin' rawks.

And geology rocks! ;-)

Ants are really fascinating. They display such a diversity of behaviors as to almost rival humans. I could not have cared less about ants until I read Dawkins. Hopefully I can get back to The Ancestor’s Tale soon; I dreamed in the Dewey Decimal Classification last night!

November 13, 2006 12:03 PM  

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