Miss USA 2011 contestants on whether evolution should be taught in schools. Just…wow.
This is fascinating. Especially Miss Hawaii’s line: “Everybody should have their opinions taught.”
This post is a continuation from my previous post, “Release the wasps (no, really, release the wasps) Part I,” which I put up on Wednesday. If you haven’t yet read it, please do, as it will provide a bit more context as to what I’m writing about today.
In my earlier post, I wrote about two parasitic, non-native wasps, which I released as a part of the USDA APHIS EAB Biocontrol program. This post will be used to provide background on the Emerald ash borer and why the decision was made to release non-native wasps in order to control it.
The Emerald ash borer (Agrilus planipennis) is a member of the sun-loving family,Buprestidae (~15,000 known species), commonly known as the Jewel beetles or the Flat-headed borers. These beetles can be found feeding from the crown downwards, on hardwoods, tending to be specialists, meaning that each beetle will often only feed on a particular species or genera of tree (This specialization is often emphasized in the common name of the beetle, e.g. the Bronze birch borer, Twolined chestnut borer, Bronze poplar borer, Emerald ash borer.) Behind this specialization are physiological and morphological implications for the beetles. Organisms that have spent a great deal of time feeding on one, or a few, closely related species will evolve mechanisms that improve their ability to feed upon that species, or genera.
I think it’s worthwhile to break this down and think about it. Evolution always favors adaptations that improve fitness.
In order to understand how the fitness of the beetle is being changed, I’m going to define a three words I have mentioned, to provide a more clear picture.
What is a mechanism? A mechanism is a process that achieves a result.
For instance, you may have seen numerous comics or jokes that involve this sort of setup (forgive me for using an academic setup here…),
Step 1. Read papers on topic of interest, decide to study it.
Step 2. ???
Step 3. Publish results!!!
Step 2., is what could be referred to as a “black box,” because one understands the input (the knowledge required to study a topic), as well as the output (publishing a paper on it), and does not necessarily need to know (unless YOU are the one performing the study), the mechanism (or work) that allowed Step 1. to proceed to Step 3.
To be more specific about my usage of mechanism now, I refer to mechanisms that improve a beetle’s ability to feed upon a tree. A general explanation could be, “evolution,” whereas more specific explanations could be, “larger or smaller mandibles” to chew with, or “chemicals specific to dissolve a particular wood tissue”, etc.
Mechanisms are what generally answer questions such as, “How does X species do Y?”
What is an adaptation? An adaptation is a particular change in an organisms biology specific to a certain situation. Examples of adaptations are: the ability to regulate body temperature (These organisms, of which we are one, are known as endotherms), coloration that assists in hiding from, or escaping predators, (also known as camouflage), and the evolution of cognition.
It is important to recognize that in the case of the beetles being able to feed more efficiently, these adaptations ARE the mechanisms which produce the resultant efficiency of particular beetle species performing well on particular trees.
What is fitness? Fitness can be defined in a few different ways, but they all fundamentally refer to the health of the organism. For the sake of synthesis, I am going to use the Emerald ash borer as an example. When the Emerald ash borer was first discovered in the United States, researchers performed a study to determine what the “host preferences” of the beetle were. These preferences refer to its propensity to eat the foliage of, as well as lay eggs upon, and chew into the phloem of particular tree species. (also see: 1,2) It was found that the Emerald ash borer would occasionally lay its eggs on species aside from ash (Fraxinus spp.), under both laboratory and field conditions, but would only eat ash foliage. In spite of laying eggs on these non-ash species, Emerald ash borer larave that attempted to bore into the phloem and construct galleries always failed, ultimately ending in death.
To be utterly facetious, death is the complete opposite of fit. I hope you’re beginning to see where I’m going- there is something about the nature of the tissues within the wood, specific to particular tree species, that makes it difficult, or rather, impossible, for an Emerald ash borer to develop on a non-ash species.
This evokes the concept of a trade-off: if you want one thing, you have to give something else up. A generalist is able to eat a little of a lot of things, whereas a specialist is able to eat a lot of a few, or one particular thing.
Since the Emerald ash borer is more of a specialist than a generalist, it would be adaptive for it to develop means to eat more ash, and less of other species. An example of a strategy it MAY (I put this in caps because there is no evidence to this claim, it is my speculation-but, if research were done, I believe results would fall along this line) employ is secreting chemicals via its saliva, that help detoxify tree defense compounds that are specific to ash species. If this speculation is true, then it would add some context as to why the Emerald ash borer performs so poorly and cannot develop on non-ash species: it doesn’t have compounds to detoxify tree defenses, the defenses overcome the beetle, and therefore, the Emerald ash borer dies.
To finally define fitness in terms of the Emerald ash borer, a fit beetle would lay more eggs and produce more of, and larger larvae, than an unfit, or less fit beetle. What I just explained above, in terms of fitness, are components that could leads to more fit beetles, with respect to the evolution of the beetle (I say this as I am not taking into account any abiotic or external biotic effects).
Now that I have defined those terms, and given context to the situation, you hopefully understand how beetles which tend to feed on and develop inside of, a few or particular species of tree, may begin to form a close evolutionary relationship with its host, over time.
This close evolutionary relationship is termed, coevolution, also known as the Red Queen Hypothesis. The Red Queen posits that if one organism is high specialized to another, so that, it could potentially cause the other to go extinct, the second organism must evolve (like a counter-defense), in order to persist. This leads to the famous Lewis Carroll quote (from which the Red Queen is named),
“…it takes all the running you can do to keep in the same place.”
This implies that the two organisms, continue to counter-evolve to each other’s evolutionary adaptations to improve their respective fitness’, in an endless struggle. Can you imagine ash trees and the Emerald ash borer, over generations upon generations, struggling against one another for dominance?
Most likely you can’t imagine this, because you probably live somewhere in the United States. One thing I haven’t mentioned yet (that if you are familiar with the Emerald ash borer, you already know), is that the Emerald ash borer is not a species native to North America, it is endemic (native to), East Asia. Because it isn’t native consider the situation above, regarding coevolution. There are two possible outcomes: (1) The Emerald ash borer is too specialized upon Asian ash, that it will fail to survive on North American ash or (2) The Emerald ash borer will be able to use its adaptations and feed very heavily upon ash that have NOT evolved defenses to it like its East Asian hosts.
Before I respond to the obvious answer above, I want to note that the Emerald ash borer in East Asia responds to East Asian ash just like our North American Agrilus respond to their respective hosts (you can find some context a few posts back, here), they become noticeable only during stressful events. What I mean, is that, Agrilus only become a problem when there is a drought, or a flood, or an outbreak of another insect, that weakens the host trees of Agrilus. Once the trees has less vigor, the beetles go to work attacking the trees. After the area has had time to recover, the beetles are maintained at low levels and are not an issue until the next big stressful event.
In North America, the Emerald ash borer does not wait until trees are weakened to attack, because it does not need to. That is why the Emerald ash borer has been deemed invasive and dangerous to the North American ash.
Look at this map of where the Emerald ash borer is as of May 2nd, 2011. It was only found in Detroit, MI in 2002 (was likely around since 1992, just unnoticed), and has spread rapidly through its own feeding, and most likely, transport of firewood.
Because the Emerald ash borer is so voracious and moves quickly due to various factors, is why biological control (the wasps I released), in conjunction with systemic insecticides, cutting of ash, and environmental education, is being used to slow the spread of the beetle; so that it may be able to be more effectively managed in the future.
Some Emerald ash borer resources:
An excellent resource.
In March 2011 issue of Trends in Ecology and Evolution (TREE), Partel, Szava-Kobets and Zobel, of the Institute of Ecology and Earth Sciences, University of Tartu, Estonia, posit a very interesting and novel way of looking at local-species diversity and the absence thereof. I feel that this timely paper will spark much contention and work over the next few years, especially considering that climate change is occurring as I write this, and species shifts/migrations beginning to be large issues. Thinking about both the observed diversity, as well as what species might be absent from a particular area, is going to be of increasing importance.
The three term “dark diversity” as the absence of species from a suitable habitat when the species exists in the local species pool. Therefore, a simple calculation of dark diversity is subtracting the local observed species from the total number of species that exist in the region that could occupy the suitable habitat. The authors acknowledge that their definition of local species diversity is similar to the definition of alpha-diversity, drawing upon the local species pool, but their definition of dark diversity is much different from the concepts of beta- and gamma- diversity. Beta-diversity is the turnover between the gamma and alpha pools of species diversity, where dark diversity only deals with species existing in a particular type of habitat. (For a brief overview of alpha-,beta-gamma- diversity, go here)
What is the take-home message about this concept? It provides a dimensionless indicator that we can use to compare different habitats or regions around the world. Three examples the authors provide are of a plant diversity across grasslands, fish diversity in different lakes, and birds in a tropical forest. A final and interesting point the authors bring up, with respect to their now dimensionless indicator, is that temperate ecosystems have higher numbers of the available species from regional pools than tropical ecosystems.
I am not the only person that finds this concept interesting. In the most recent issue of TREE are two responses to the original paper, and a third by the authors. You can find them below.
One thing that I am fascinated with more than anything else is is strategy. Usually equated with games of the mind such as chess, rather than everyday life, strategy can both subtle or overt, but when it comes to the end of the day, it’s all-encompassing.
Another thing I’m pretty head-over-heels for is public radio. If you don’t listen to public radio, honestly, you should. There is so much variety and tons of quality programming. So now you’re wondering why I’ve completely changed the subject and have gone off on a tangent…Well, it’s because, by the glory of all things good in public radio and science, there just happens to be a show that took on this very issue. That show, RadioLab, does an absolutely excellent job not only on this one specific episode, but in general. I won’t ramble too much more about it, but know that it’s a worthwhile listen for anyone interested in science, be it on those actual radio things, or as the free podcast.
Finally, the show, entitled, “The Good Show” covers a few of the basics regarding what strategy is, what strategies there are, and a few of the key players that and involved in furthering research on the subject.
On that note- you should go listen to it…
But before I end this brief post, let me just introduce you to a simple thought experiment that has been foundational to research on strategy.
This though experiment is something you may very well have heard of before, it’s called, “The Prisoner’s Dilemma.”
Imagine two crooks, bank-robbers,murders, or some other type of criminal offenders have been caught for a crime. Although apprehended, the police don’t have quite all the evidence they need to really put the two in the slammer for committing the aforementioned crime(s). So, what the police decide to do is split the two prisoners up for a period of time then take each one, individually into a room and say…”your other guy, you know he ratted you out, you’re going to go away for 5 years in prison…But, if you spill the beans on him, we’ll make you a deal, cutting that time, to only a year.” The prisoner ponders this offer and has to decide whether he is going to reciprocate against his partner, or if he is going to keep silent and not say anything. These two options are now to be referred to as “defect,” and “cooperate,” respectively.
Here’s the kicker, the police don’t actually have much evidence at all, and-they’re liars. The other prisoner did not say anything, in fact, the police have yet to even meet with him yet. They are trying to trick the prisoner into giving them the testimony they need in order to convict him and his accomplice.
So let’s step back away from the thought experiment for a moment and consider that each prisoner has two unique choices he can make. We can therefore look at all the possible outcomes just like a Mendelian punnett square
There are four possible outcomes:
(C,C), (C,D), (D,C) and (D,D)
where C= cooperate and D= defect
It’s easy to understand the outcomes of each of these situations by assigning a value to each decision and outcome. The graphic to the left (which I’m so graciously borrowing) assigns the most logical values for this situation, “years in prison.”
So lets run through these situations:
(C,C) where both prisoners cooperate they both get 2 years in prison
(C,D) Prisoner 2, Henry in the case of the graphic, defects, squealing on his partner, leaving him with a quick 1 year in prison and his partner with 5 years in prison.
(D,C) Prisoner 1, Dave, defects, and ends up with the same deal as Henry would have if he defected, 1 year in prison for the rat, and 5 years for the transgressed.
(D,D) Both Prisoners 1 and 2 defect, giving testimony that the other was the leader of the crime, and they were simply the accomplice. Due to the contradiction, neither can be fully convicted, but they still both end up with 3 years in prison each.
SO. What is a prisoner to do? It’s obvious if this testify that their partner was in charge that they will receive the least amount of time in prison. If they say nothing, they will end up with more time in the slammer. This is where the dilemma comes in. Both prisoners are told that their partner ratted them out. This means, if they believe the police officers words, then they will go away for 5 years and their partner will get off with a much reduced sentence. So what is to be done?
None of the options are really obvious to the prisoners as they are not privy to exactly what evidence is held against them. They also cannot speak with their accomplice to confirm or deny the statements made against them.
Again, I ask, What is a prisoner to do? Well, Robert Axelrod, a professor of public policy at the University of Michigan, wondered the same thing. Except, he approached the problem with a little more robust treatment than just thinking and anecdote. Axelrod decided an excellent way to determine what to do was to hold a contest. The guidelines of this contest were relatively simple, contestants would write a program that would “play out” this situation a number of times, against a program of another contestant. Instead of “years in prison,” point values would be assigned to the programs, based upon their decisions, respectively. The highest point value would be assigned to the best outcome, or the least amount of time in prison. Therefore, the prisoner who defected against his cooperating accomplice would receive the most points.
By running these simulations over time, particular strategies, or (sometimes) conditional behaviors would be highlighted as good, bad, better, etc. Therefore, one could use these as guides as to what to do in the Prisoner’s Dilemma. I’m not going to elaborate too much on these strategies, except for the winning one, was known as “Tit-for-Tat,” which I believe Wikipedia does a good job of explaining (this is verbatim from the site):
- Unless provoked, the agent will always cooperate
- If provoked, the agent will retaliate
- The agent is quick to forgive
- The agent must have a good chance of competing against the opponent more than once.
In the last condition, the definition of “good chance” depends on the payoff matrix of the prisoner’s dilemma. The important thing is that the competition continues long enough for repeated punishment and forgiveness to generate a long-term payoff higher than the possible loss from cooperating initially.
A fifth condition applies to make the competition meaningful: if an agent knows that the next play will be the last, it should naturally defect for a higher score. Similarly if it knows that the next two plays will be the last, it should defect twice, and so on. Therefore the number of competitions must not be known in advance to the agents.
Therefore, always cooperate, and if someone burns you, burn them back; but be forgiving.
That’s the Prisoner’s Dilemma, foundational for a basic understanding of strategy, and a central tenet of game theory.
Thanks for sticking with me for the rather lengthy explanation. Now if you haven’t already, GO LISTEN TO RADIOLAB. It’s a great show and the episode features Robert Axelrod, who does a much better job explaining his own work than I.
If you’d like to pursue this subject a little bit further I’d suggest two books, one which is rather technical (read: full of math) and the other, which is written towards a popular audience, but still features all of the meaty bits of science (sorry I can’t equate science to veggies folks)
Read: “Evolution and the Theory of Games” by John Maynard Smith
Read: “The Selfish Gene” by Richard Dawkins
Just got this on ECO-LOG. Free video lectures. Check it out.