the controversy
Remember how I told you that local adaptation is a slippery slope?
There are several reasons why local adaptation can be a difficult concept with which to work. Here are at least 3 that I have been grappling with:
1. Local adaptation is still a very controversal subject.
Remember that Edmunds & Alstad paper on on the black pine leaf scale that I mentioned in my last post (1978)? I said that it is a classic example of local adaptation. Well, that is not entirely correct. I should have said it was considered a classic example of local adaptation. Alstad has since recanted the results and conclusions of the study due some problems with the experimental methods (Alstad 1998). Other sceintist criticized the experimental methods, in particular the locations of the natal and novel plots relative to each other (Unruh & Luck 1987). Although this particular study has been strongly criticized, other scientists have gone on to design experiments that took these errors into consideration. Some of them were successful in finding evidence for local adaptation, while others were not.
2. The empirical evidence for local adaptation is not overwhelming.
By 1998 there were at least 17 studies on local adaptation in natural populations (Van Zandt & Mopper 1998). Even with more empirical evidence, the status on local adaptation remains controversal because the evidence is split in support and refuting the existence of local adaptation. This low number of empirical evidence in support of local adaptation may be due to the issues that confront those of us interesting in finding it. It is difficult to do reciprocal transplants and other experiments testing for local adaptation on natural populations in the field. Many problems are due to underreplication (Boecklen & Mopper 1998). The statistical power to detect a difference between the fitness on a natal or novel host is extremely difficult with low replication. Considering the difficulties in finding statistical evidence for local adaptation, I find it encouraging that it has been found. I also encouraged by recent evidence for genetic differentiation in a suite of insect species on 2 different species of goldenrod (Stireman et al. 2005). I will talk about this study at great length in future posts (I can tell you are at the edge of your seat).
Goldenrod photo from usn. This one is for you scott.
3. Local adaptation and adaptive deme formation - Is it merely a question of spatial scale?
Local adaptation is also termed adaptive deme formation. The Adaptive Deme Formation Hypothesis (aka ADF) was coined by the aforementioned Edmunds and Alstad in their 1978 paper. A deme is usually defined as an interbreeding population of the same species. ADF and local adaptation are used interchangabley by some. It is confusing whether they really mean the same thing. Afterall, when Edmunds and Alstad used it, they were referring to localized demes adapting to an individual tree. Local adaptation, on the other hand, can refer to any spatial scale. An organism can be locally adapted to a tree, to a host plant species or to a site. Are these terms interchangable? Or can you use ADF as long as you define a deme in your particular case?
That is all for today. Please leave comments and questions.
There are several reasons why local adaptation can be a difficult concept with which to work. Here are at least 3 that I have been grappling with:
1. Local adaptation is still a very controversal subject.
Remember that Edmunds & Alstad paper on on the black pine leaf scale that I mentioned in my last post (1978)? I said that it is a classic example of local adaptation. Well, that is not entirely correct. I should have said it was considered a classic example of local adaptation. Alstad has since recanted the results and conclusions of the study due some problems with the experimental methods (Alstad 1998). Other sceintist criticized the experimental methods, in particular the locations of the natal and novel plots relative to each other (Unruh & Luck 1987). Although this particular study has been strongly criticized, other scientists have gone on to design experiments that took these errors into consideration. Some of them were successful in finding evidence for local adaptation, while others were not.
2. The empirical evidence for local adaptation is not overwhelming.
By 1998 there were at least 17 studies on local adaptation in natural populations (Van Zandt & Mopper 1998). Even with more empirical evidence, the status on local adaptation remains controversal because the evidence is split in support and refuting the existence of local adaptation. This low number of empirical evidence in support of local adaptation may be due to the issues that confront those of us interesting in finding it. It is difficult to do reciprocal transplants and other experiments testing for local adaptation on natural populations in the field. Many problems are due to underreplication (Boecklen & Mopper 1998). The statistical power to detect a difference between the fitness on a natal or novel host is extremely difficult with low replication. Considering the difficulties in finding statistical evidence for local adaptation, I find it encouraging that it has been found. I also encouraged by recent evidence for genetic differentiation in a suite of insect species on 2 different species of goldenrod (Stireman et al. 2005). I will talk about this study at great length in future posts (I can tell you are at the edge of your seat).
Goldenrod photo from usn. This one is for you scott.
3. Local adaptation and adaptive deme formation - Is it merely a question of spatial scale?
Local adaptation is also termed adaptive deme formation. The Adaptive Deme Formation Hypothesis (aka ADF) was coined by the aforementioned Edmunds and Alstad in their 1978 paper. A deme is usually defined as an interbreeding population of the same species. ADF and local adaptation are used interchangabley by some. It is confusing whether they really mean the same thing. Afterall, when Edmunds and Alstad used it, they were referring to localized demes adapting to an individual tree. Local adaptation, on the other hand, can refer to any spatial scale. An organism can be locally adapted to a tree, to a host plant species or to a site. Are these terms interchangable? Or can you use ADF as long as you define a deme in your particular case?
That is all for today. Please leave comments and questions.
posted by bugheart at 3:00 PM
5 Comments:
This is great! I can't wait to be the world's "second most authority" on local adaption and what ever it is you do!
Keep on writing! I will keep on reading.
XOXOXO-
Mel
first of all, let me say that this is cool, and i am happy to see it, and to try my hand at this interweb i have heard so much about.
so, the controversy over local adaptation basically comes down to, does a separate gene pool exist for individuals of the same species in different (though maybe nearby) places? and, if so, is it reinforced by some adaptive significance, so that if they get taken out of their good and happy place and put in the bad place, they won't make it, due to some gene(s) that work better in the happy place?
obviously you're trying to give yourself the best chance for finding local adaptation in whatever system you pick. so proposal-wise, you should mention why people haven't found local adaptation who have looked for it, and why the magical system you're about to explore will avoid those problems. you mention that people haven't had good replication. is that because of the reduced reps you get when doing breeding experiments? do you need to do the good old sire-dam randomization type stuff in looking for local adaptation effects? can you avoid the replication problem by looking at a well-reared species (cough orgyia cough)?
also, the scale (spatial, not insect type) question is interesting and something we should talk about. to my mind the important thing is that the "locality" is big enough to encompass only one interbreeding population under similar pressures which might force it to adapt. if it's more than one pop, you won't see it, and if it's less than a full pop, then you're only getting part of the picture. this is in theory of course. in practice, it will pretty much be dependent on the dispersal capabilities of the organism you're interested in. for all a scale insect cares, a tree is a locality, but for a caterpillar it may or may not be, and for an adult moth it definitely isn't.
so i could go on. but like i said, this is cool. keep it up.
i keep thinking about the fact that the studies you mentioned where local adaptation has been observed involve species that in one way or another don't move around much, like scale insects (we talked about this once). i know that in the goldenrod study the species where some differentiation was found were somewhat immobile. i guess my question is, of those 17 works that support local adaptation, how many involve species that are not "stuck" in some way? i am very curious.....
i also have a question regarding the studies- are we mostly talking about plant feeders? or are there some predators in the mix. and do most of the papers discuss insects that are specialists, or generalists? would local adaptation be more likely to occur with a specialist? maybe these are no brainers, but that is what I am thinking about!
I think the range of dispersal is the spatial scale that is most important when considering local adaptation. If they can't get there, they should't be adapted to it. (Hence trees in some cases, flowers in others, fields in others.) This in itself is a huge problem because its often hard to know what is an appropriate scale for an organism.
I really like MikaJ's question: what role does specialization play in this? Part of me thinks that a specialist could be more likely to be locally adapted because of the dogma that specialists are specialists due to adaptation. However, it is interesting to note that more and more studies are showing species that are considered "generalists" are actually a collection of specialists to different hosts. (Local adaptation? I would say so.)
:) Julie
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