Macroevolution: Its all around us...

I know Quig has left himself wide open on some of his posts,
and I suppose we could all gang up on him for it,
but what would that accomplish?He has to demonstrate a desire to understand first,
and make his commentary a bit more responsible.That is why I would appeal to all to discuss, supportively or critically, some of the more interesting examples of macroevolution that people have posted on this thread.The last really good one was the stick insect phylogeny from the Nature article posted by RazD. THAT is a macroevolution. I presume the cladogram in the chart is based on genetic distances calculated by molecular markers, but I don't have full access to the article out here on the high prairie.Do we accept this cladogram ?
Can we conceive of conditions that would lead to the loss of flight in an insect lineage once it had evolved?
If you can fly, what advantage could there possibly be to loss of the ability?Just some questions to try and get us back on topic, because I really don't think there is any rationale need to defend the fact that genomic information can increase - it's trivializing the discussion at this point.EZ

For those unable to access the Nature paper cited by RAZD, I've uploaded the important figure to a web server. At some point my server may bum out (I think it has a maximum band width per month) but if that happens i'll put it somewhere else.Reference: Whiting et al (2003) Loss and recovery of wings in stick insects. Nature 241: 264-267 The tree was generated from aligned18S and 28S ribosomal RNA, and histone 3 dna. The tree is a maximum likelihood tree. Character states were mapped onto internal nodes of the tree using maximum parsimony.The most parsimonious reconstruction of evolutionary events is that there were three wing losses and four wing gains in this clade. What's interesting is that the character states of the living species are very diverse. The Neohirasea lineage has undergone a loss, a gain, and onother loss of wings since divergence from Oligotoma (which is the outgroup to the tree, and is not a stick insect but a webspinner (Embioptera)).If I wanted to guess at the genetic architecture underlying these transitions, the fact that reversions like this are common suggests to me that the "genes" for being winged are not lost when the winged phenotype is lost. It strikes me that the genetic changes must be in the developmental system. As far as I know, stick insects only have wings in the reproductive stage of their life, so the maintenance of winglessness into adulthood represents an extension of the immature phenotype into the reproductive phase.But is it macroevolution? I suspect that some people here might say that, while the loss or gain of wings is a large phenotypic change, these species are all "still stick insects", and that we are only seeing microevolution here.For those people, it would be interesting to know what they make of the loss of wings that occured at the base of the tree (loss of wings in stick insects relative to web spinners). If wing gain or loss is microevolution when it occurs within the stick insect clade, does the initial loss of wings at the common ancestor of stick insects constitute macroevolution?Mick

thanks mick!I agree that it is just speciation, but I also note that if we parse the mechanism to it's most parsimonious minimum, all we have in evolution is speciation evolution: an accumulation of {physical\behavioral} changes sufficient to prevent previously related populations from interbreeding.In this regard the DNA evidence is the same: changes upon changes accumulating over time.Any attempt to create larger classes is just a result of subjective analysis due to apparent magnetudes of differences.In this I have been converted.

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

I agree with you on that, but I suspect those who aren't convinced by macroevolution would want to see the kind of analysis described for walking sticks carried out for a trait that is directly related to speciation, or a trait that is diagnostic of a major group of animals. Wings on stick insects isn't going to do it, because wingedness is characteristic of all sorts of insects, not unique to stick insects. Any variation involving wingedness is always going to be "variation within a kind".I wonder if there are any papers on the evolution of the hexapod body plan? Now that is a trait that is diagnostic of insects per se, and if its evolution can be explained then we have a clear example of macroevolution in a trait related to speciation of a major group.Other examples we might look for are: evolution of aquatic lifestyle in whales; evolution of eusociality in hymenoptera; the origin of flight in bats; loss of wings in worker ants; origin of desalination ability in mangroves; origin of year-long greenness in pines; origin of the cerebral cortex in crocodiles; etc.These are evolutionary events that are undeniably macroevolutionary transitions. There must be dozens of papers that deal with such issues in a phylogenetic context, similar to that used for wingedness in stick insects. I'll take a look in the databases at some point.Best wishes

have you seen the work by Jim Marden on the evolution of flight in stoneflies?http://www.rps.psu.edu/jun95/marden.html

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

very cool! I hadn't seen it. That is the kind of evidence we need, accompanied by knowledge of the phylogenetic position of stoneflies in insects (I think they're pretty primitive).Thanks!

I just want to clarify some inferences from Micks original response first. I concur. This would make repeated gain and loss in the lineage so much easier. Exactly. It would be an example of 'neotony' - the maturation of a larval form. Far easier to accomplish in Phasmids than in other insect orders such as beetles and moths because they don't have complete metamorphosis - they are 'hemimetabolous'. Juveniles forms are not 'larvae' but nymphs - small versions of the adult already.On the genetic level, the loss / gain events become much easier to explain. They simply represent changes in the end-point of development to an earlier (loss) or later (gain) stage. The deeper inference is that ALL the genes encoding wing development do not need to be gained or lost for each event. They could (most parismoniously) be just expressed or not expressed depending on whether or not a single operon gene is switched on or off.{Added in edit} So now we can gain some perspective on why this whole 'loss' or 'gain' of information on the genome crap is so irrelevant. These changes require neither ! It's just a toggle switch being thrown back and forth !{end}Now the more interesting question is whether these gain / loss events could have had implications for speciation patterns via reproductive isolation events.
I submit they certainly could have, but they would have to affect mate choice.{added in edit} If wingedness DID after mate choice, it could result in almost instantaneous speciation events, and possibly be a driving force in determining the cladistic pattern observed. {end}And RazD is exactly right - the only bifurcations in a lineage of any REAL consequence are speciation events. After that, relatedness is simply some function of genetic distance or 'similarity', however you choose to measure it.But no one has answered this question:What are the ecological conditions that would favor these neotonic aperous (wingless) taxa over their alate winged counterparts ?I have an idea myself but I want to hear others first.On another tack, Mick - could you perhaps clarify this procedure of character mapping to the genome ? How is the correspondence established between 'gene' and 'trait' ? Always been a mystery to me.EZThis message has been edited by EZscience, 05-14-2005 07:33 PMThis message has been edited by EZscience, 05-14-2005 07:47 PM

I would think that a very thick {undergrowth\'jungle'} environement would select against flight as a waste of developmental energy when you can't fly further than you can walk, but that more open environments would select otherwise.and it would be logical for some environments to evolve back and forth depending on climate changesmy "tutu sense" worth of the dance ...

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

I submit that we might have to consider the 'ecology' from a life-history perspective.Wouldn't there be some physiological costs to having wings...
(hint)

Hi EZscience, Do you mean to ask how we map a character onto a phylogenetic tree in order to infer the existence of historical transitions? If so, I can answer your question.If you really do mean "how do they map the phenotype to a gene", i.e. physical mapping of a trait to a specific chromosomal location, that is not something I can help you with! (It's also not something the athors of the walking stick paper did).Mick

Yes, the first.
I assume that the tree is inferred from mtDNA sequence homology, but then how is the trait superimposed on the tree ?
Do they just examine extant forms of these lineages ?
How can they determine the character states on the extinct lineages ?

okay, I'll post an overview some time over the next day or so. It's not that complicated, but if I just give a quick answer it will likely seem unconvincing.cheersMick

one big advantage to being wingless is you are not limited in size.but then the "Goliath Walkingstick" Phasma gigas flies (well the male does, the female doesn't).Page not found - Bugs In Cyberspacethis stick is about 7" long.

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

Well I would say you are on the right track.But size is also relative.If you develop wings, you are partitioning resources to wings and wing muscles, resources that could be used to get bigger OR, perhaps more importantly, to devote to reproduction.So winglessness would pay in rich environments where food was consistently available (perhaps your jungle) and where dispersal capability was not worth the physiological cost of wing development.However, in poor or unpredictable environments dispersal becomes more important to find food, and the reproductive tradeoff for wing development quickly becomes worth it.Note that in your Phasma gigas the female remains flightless.
This is significant.
That way she can produce more eggs. The male produces inexpensive sperm and can more easily 'afford' to develop wings.After all, the finding and mating of females is all that matters and wings would be of greater benefit to males than females here.
Same story for the gypsy moth, Lymantra dispar.In parallel, most of the aphid species I study produce both winged and wingless morhs (and sometimes some other forms as well), but the apterous morphs always have 3-5 times the fecundity of the alate morphs. And the alate morphs are only produced when the colony is losing/destroying its food source and needs to find another."the finding and mating of females is all that matters..."
Some guy should use that as a signature...This message has been edited by EZscience, 05-15-2005 09:45 PM

yeah, that ties in with "select against flight as a waste of developmental energy" in a previous message. and that is what makes sexual selection significant in it's own right, as this need can trump mere survival if there are no mates left.

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}