Wednesday, October 11, 2006

Is there a Darwinian first mover advantage?

This is a question for any biologists who happen to tune in. In 1981 I was building a house in Massachusetts and spent many days out doors. That summer a massive infestation of gypsy moths denuded the oaks and their droppings fell like rain. The next summer I found a few dead caterpillars, turned into little bags of pus by a fungus called Entomophaga maimaiga. I gave the parasite a leg up by collecting the dead gypsy moths, making a puree of them and freezing jars of this puree to paint on my trees the next season. By 1984, when the moths were picking the trees in the north part of town clean, I hardly saw any damage. My neighborhood has been nearly free of the pests since then. My observation is that humid weather favors the fungus and so drought is when the trees are hit the hardest both for water and from the damned moths. I have a way to mist my woods if need be to insure the survival of my cultured fungi but it has not been necessary yet. I imagine the local moth and fungus populations are now locked in an evolutionary war.

Since selection of fittest requires a reasonably consistent application of some "selection pressure" to prevail in the environment, Darwinian success comes from a reaction to circumstances. This means that the great survivors often have succeeded by doing what humans caution themselves NOT to do: plan and provision for winning the previous war. A species that can manipulate genes in anticipation has a huge advantage in the world as Darwin has explained it to us.

The Question: In the natural evolution battles, does any advantage go to the first antagonist that can nearly wipe out its nemesis? Once ahead, do they stay ahead? Is the logic entirely different for host/parasite compared to two species competing for the same resource or niche?

How far can one stretch a generalization? I know that if you only see Darwin's idea as promoting individuals that can outfight, out forage or outf__k, you miss the whole idea of cooperative adaptation being selected...its a natural mistake for conservatives to make. But when evolution driven by the competion of host/parasite is the context, can you just assume an arms-race like spiral where the balance see-saws from time to time as long as the environment is supporting the host? Probably not that simple but there are certainly applications if it is: I want biological control of winter moths which are presently denuding whole forests in not-too-distant parts of Massachusetts...I want to head them off with a well tuned parasite before they get started. After that, if things are so simple and there is a first mover advantage, the blighters will be held in check as they battel with the germs I give them.

7 comments:

jan said...

Your questions are too broad and varied for me to answer with my limited knowledge, even tho I worked on a gypsy moth project for years. However, your comment
"A species that can manipulate genes in anticipation has a huge advantage in the world as Darwin has explained it to us."
is a bit off. The species does not manipulate genes, the species does not anticipate. Nor do individuals.
The definition of fittest is the individual that survives to produce the most offspring. Period.
"Fitness" can change from moment to moment. Whatever genotype was fittest yesterday may not be fittest today if the environment changes. That's why variation of genotypes within populations, fostered by sexual reproduction and the resultant recombination of genes during meiosis-- is important. A species or population with a variety of genotypes will be less likely to die out completely when the environment changes because some will be the fittest for the new environment.
And random mutations and combinations of genes during meiosis (sexual production of offspring) are what give the members of the population the goods to survive in the future or not.
As for host/parasite relationships, that's a bit more comlicated and something about which I can't remember. My suggestion would be to look up co-evolution and read things by Stephen Jay Gould. He was an extremely prolific writer, and he stressed over and over that nature has no values, no conscience. I am out of the entom. field now so can't suggest more.

You raise good questions tho. My guess is that your efforts with smearing fungal residue had little effect,overall, but who knows for sure. It depends at which larval stage the various pathogens are introduced or effective; the gypsy moth caterpillar behaves differently during different stages of growth. I'd say why not do it again with the new moth pest as long as you feel it might be worth it and as long as you have the time.

GreenSmile said...

Thanks, Jan. Your point about "species that can manipulate genes in anticipation" is correct and shows up some rather sloppy writing on my part.
Without reference to any particular species and using the normal meanings of the biology vocabulary, no, there is nothing like anticipatory gene selection at any agregation from individual to species.
What I meant was that we 21st century humans do have the capacity to anticiapte, at least the scientifically trained among us. And, in the agency of our laboratories we have the capacity to try random or hybridized or more precise manipulations to see if we can't breed up bugs that will help us against a not-yet-realized threat. Our work on bird flu is in this spirit though not using the mechanism of breeding more resistant humans.

I would quibble that as a definition "...fittest is the individual that survives to produce the most offspring" omits such possibilities as social insects where most individuals are self-sacrificers but that trait is co-evolved with a fecund breeder they support: the individuals manifestly do NOT survive or reproduce yet their species thrives. You really have to have both competition and cooperation in the evolutionary model.

You do make it clear that host/parasite really is a very different set of rules from the competion of two parallel species in the same niche. The point that the range of variations within a species which sexual reproduction permits is a good strategy against selection pressures that vary rapidly is important. It complements my oversimple notion that major genetic shifts and whole new species require steady and continued selection pressure. Neither time scale is exclusively applicable. And yes, I owe Gould a good read.

I will have to find out if that fungus or any other bug [BT?] is already an effective natural pathogen for the winter moth. I certainly haven't worked with enough controls to certify that my application of the puree had any effect. And maybe it was just luck. The fungus may always be present as spores but only able to arise from dormancy and infect in damp conditions...nothing that I did would have impacted the results in that case.

Thanks for the thoughtful reply

Davo said...

um, the Cane toad (Bufo marinus) was introduced into Australia by humans ïn 1935 as a "control" against economic "pests".

Darwinian evolution operates very slowly in Australia. At this point there are still no "natural predators".

(Though as a bright note have heard that some herons are learning to turn the bastards onto their backs and peck out the belly .. but that is yet unconfirmed)

GreenSmile said...

In fact Davo, the gypsy moth itself was an introduction from europe. Some greedy nitwit thought they'd be able to make a silk industry in the chilly New England climate.

Seeing as how Oz has such "left behind" creatures as the platypus, you must be right that evolution is happening in slow motion there. But you may be better of than Canada, of which one of its native bloggers has asked "But does evolution believe in Canadians?"

jan said...

GS, Oh, I see what you meant about humans anticipating and manipulating. Right.
And yes, you are right that social insects are a separate case. Biologists look at a colony of social insects under one queen as a superorganism since the non-reproducing individuals do seem to sacrifice themselves for the whole. It seems to me it's been calculated that, percentage-wise, the genes of the infertile 'sisters' within a colony are still reproducing at a better rate than if they'd reproduced on their own...I can't remember much more. And of course being social apparently works.
The biological world (unlike the world of physics) is full of gradients rather than distinct categories, and it's always changing. This is what so many antiscience people can't quite get: science is a quest to understand and learn, but upon learning more we end up with more questions!
Chances are good that bt works with the winter moth larvae, but you'd have to apply it to leaves in the canopy since they have to eat the stuff for it to work.

Davo said...

um, actually meant to include this link as a sort of background to my previous comment, but forgot. Human beings have a peculiar propensity to meddle with the "natural" order of things, with sometimes unfortunate results .. heh.

Davo said...

and further to that comment .. we seem to have acquired this "need for speed", and one of the things that troubles me about "gene manipulation". Yes, we have been "selectively breeding" stud stock since agriculture began, but that happened over many generations of process allowing time for species to adapt. The sudden introduction of a "new" species may well fit into the concept of Darwinian evolution if it is predicated on the survival of "the fittest", since the new species has no predators, and may well "take over" to the exclusion of all others.

We tend to forget that the incredible and rich diversity that the earth contains (or used to contain)has adapted and managed to co-exist; developed over MILLIONS of years.

(Hopefully Walmart, Microsoft and George W. Bush are but passing phases .. heh)