What comes to mind when you think about insects? For a lot of people, the word sends a shiver up their spine as they imagine the tiny, creeping legs, buzzing wings, stinging tails, and biting fangs. But what those people may not know is that insects comprise one of the most important classes of animal; there are more species of insect than any other animal group, and they can claim being the first animals to achieve many things, including flight and social societies.
Insect evolution is historically poorly understood, and the lack of a well-resolved and supported tree of insects has left researchers with many questions about their evolutionary relationships. For example, how are grasshoppers, crickets, cockroaches, and termites related? Which species are the closest living relatives to Holometabola, the group containing beetles, moths, butterflies, wasps, bees, and ants? What is the timeline of insect evolution? Answering these questions could help us understand how different insect traits evolved, which could reveal insights into the mechanism of evolution itself.
Silverfish (left) evolved to lose their wings and other appendages independently from other insects like jumping bristletails (right), and they make up their own branch on the new phylogenetic tree of insects.
Images: Wikipedia
Scientists with the international 1KITE project set out to answer these questions and more by using phylogenomics to compare 1478 genes among 103 species of insect. First, they sequenced the DNA to find genes that were present in all the species, most of which coded for proteins involved in translation, protein transport, neurogenesis, and other basic cellular functions. Similar to the study of birds that we talked about last time, Misof et al. used improved methods of analysis to reduce errors from such a large dataset. Before analyzing the data, the researchers accounted for possible sources of bias by removing confounding factors; for example, they removed any data that violated the assumption that evolution is a time-reversible process. They then discarded any sequences that were misaligned and generated their tree with maximum likelihood models as well as a partitioning scheme to improve the accuracy of the assumed model of evolution. Using data from two sources, nucleotides and amino acid sequences, the researchers generated two matching phylogenetic trees.
The new phylogenetic tree was able to answer many questions about insects with a higher statistical confidence than previous studies:
Earwigs, ground lice, stoneflies, crickets, gladiators, ice crawlers, webspinners, stick and leaf insects, praying mantids, and termites comprise a branch on the tree (a monophyly) called Polyneoptera, a hypothesis proposed in previous studies.
The study proposed the new conclusion that lice are the closest living relatives to beetles, moths, butterflies, wasps, bees, and ants.
Insects originated around 479 million years ago, a finding that contradicts previous estimates of about 400 million years ago.
Insects inhabited land at about the same time as plants (around 450 million years ago) and developed flight after they had established colonies, corroborating a 2013 study.
Remipedia, a class of blind crustaceans found in caves, is the closest living species to insects, confirming prior studies.
Silverfish comprise their own branch on the tree, as other recent studies have proposed, implying that they evolved to lose their head endoskeleton, leg-like structures called styli, and the sacs on their legs (coxal vesicles) in parallel to but separately from winged insects.
While many of the conclusions drawn by the new study are not completely new findings, the history of insect evolution is controversial and relationships previously proposed lacked certainty. The ability of the 1KITE researchers to confirm and deny these relationships with such high confidence shows the power of genomic analysis. But as with the recent bird phylogeny paper, the methods of analysis had to change to accommodate a larger dataset; specifically, confounding factors that could lead to biased conclusions were a larger concern than for previous studies. Jarvis et al. chose with their bird analysis to modify their programs to create a better phylogenetic tree, while Misof et al. removed data with these confounding factors during analysis. It remains to be seen which genomic data analyses produce the best results, but what we do know is that genome sequencing will play a major role in future phylogenetic studies of all species.
This series is supported by NSF Grant #DBI-1356548 to RA Cartwright.
37 Comments
John Harshman · 29 January 2015
Unlike the bird paper, this one is paywalled. What's all this about silverfish losing their wings? And what's the evidence that they lost whatever independently of jumping bristletails?
mattdance18 · 29 January 2015
Quick question about the silverfish. The picture caption indicates that silverfish "lost their wings." Is there any evidence that they ever had wings? I thought that wings were one of the derived features of the Ptergygota, to whom the silverfish are the sister group.
The parallel losses of head endoskeleton, styli, and coxal vesicles seem to be implied by the tree, as the basalmost silverfish, Tricholepidion, still has them. But wing loss for the whole Zygentoma lineage, too? That would be news.
I ask because I am not a subscribe and therefore cannot access the article. Does it discuss this? Not trying to be snarky, just wanting clarification.
mattdance18 · 29 January 2015
John Harshman said:
Unlike the bird paper, this one is paywalled. What's all this about silverfish losing their wings? And what's the evidence that they lost whatever independently of jumping bristletails?
Glad to see someone else wondered about the wing situation.
And yeah, I too am wondering about the bristletails comment. I thought that bristletails still had these, just like the silverfish Tricholepidion. It's one of the reasons why the placement of Tricholepidion matters. I've seen it claimed that it should be on its own lineage sister to [remaining Zygentoma + Pterygota]. So I'm very curious what the article itself actually says.
callahanpb · 29 January 2015
Sorry if I sound like a complainer, but I didn't like the intro to this article. I think most people who would want to read the content are strongly in the camp of those who find insects fascinating and associate them with hours of childhood bug-watching.
Joe Felsenstein · 29 January 2015
The link for "partitioning scheme" leads to a page on partitioning hard disks. No doubt important, but probably not what was intended.
DS · 29 January 2015
I was pleased to see that the crustaceans are shown as the sister group to the insects. This is a relationship supported by the mitochondrial gene order data.
I was also pleased to see that this study confirmed the sister group relationship between the Siphonaptera (fleas) and Mecoptera (scorpionflies). I have done some work on the sperm morphology of hangingflies and this is what the sperm morphology also indicates. Common design it is not.
Soon the trolls will appear to claim that it is just a line of reasoning, or circular reasoning, or whatever. I will ask them in advance to explain the congruence of the molecular and sperm morphology data and the distinct lack of any common morphological similarities between the groups. If they cannot, then any pissing or moaning that they do can be safely ignored.
John Harshman · 29 January 2015
DS: Clarification. Crustacea isn't the sister group of the insects. Crustacea is paraphyletic to the insects, whose sister group is the remipedes.
mattdance18 · 29 January 2015
DS said:
I was also pleased to see that this study confirmed the sister group relationship between the Siphonaptera (fleas) and Mecoptera (scorpionflies). I have done some work on the sperm morphology of hangingflies and this is what the sperm morphology also indicates. Common design it is not.
I'm actually a little curious about this one. I thought that recent molecular and morphological studies indicated that fleas were actually sister to one family of scorpionflies, the Boreidae -- whose common name is, coincidentally, the "snow fleas." So the Siphonaptera aren't sister to the Mecoptera: they are a very specialized lineage of Mecoptera. It does look like they included Boreus in the analysis, and it ends up being the basalmost line of scorpionflies. And then they've got the whole group, Boreus included, sister to the fleas. But I would be curious to see what the paper actually says about this.
Anybody able to read it?
callahanpb said:
Sorry if I sound like a complainer, but I didn't like the intro to this article. I think most people who would want to read the content are strongly in the camp of those who find insects fascinating and associate them with hours of childhood bug-watching.
From an interested layman's perspective, I found this article very interesting, and the intro quite apt. I used to be a tour guide in some of the caves of Derbyshire, which is an area nicely mixing Carboniferous limestones, sandstones and coal measures. Our visitors were usually polite when I enthused about brachiopod fossils in the walls, but their interest wasn't really piqued until we mentioned some of the big bugs found in the coal mines near Bolsover. As the intro to the article points out, many people can't stand them, and the thought of a dragonfly with a four-foot wingspan or a six-foot millipede really caught their imaginations. Hopefully they spent the rest of the tour half a mile into a hillside wondering when something was going to start scuttling towards them (though the biggest things living inside were cave spiders, chunky but harmless)!
DS · 30 January 2015
so booby, why is flea dna so similar to scorpion fly dna? is it like looks? if not answer then creation points disregarded as only line of reasoning with no biological evidences
DS said:
so booby, why is flea dna so similar to scorpion fly dna? is it like looks? if not answer then creation points disregarded as only line of reasoning with no biological evidences
This is not directed to any one person:
Is the similarity due to:
a) chance
b) natural constraints
c) design goals
d) none of the above
DS · 30 January 2015
John Harshman said:
DS: Clarification. Crustacea isn't the sister group of the insects. Crustacea is paraphyletic to the insects, whose sister group is the remipedes.
Thanks for the clarification. I was not aware of that. My point was that the crustacea are more closely related to the insects than are the myriopods, as the phylogeny clearly shows, that was a big controversy for some time. It would certainly be interesting to know the mitochondrial gene order of the remipedes.
DS · 30 January 2015
TomS said:
DS said:
so booby, why is flea dna so similar to scorpion fly dna? is it like looks? if not answer then creation points disregarded as only line of reasoning with no biological evidences
This is not directed to any one person:
Is the similarity due to:
a) chance
b) natural constraints
c) design goals
d) none of the above
Well obviously it is due to constraints on design. Obviously the dna controls the sperm morphology and nothing else about the looks. god just cares about the looks of the sperm, nothin else. What is ya, ignorant?
DS · 30 January 2015
If anyone is interested, I did find this article about the remipedes:
http://decapoda.nhm.org/pdfs/38922/38922.pdf
DS · 30 January 2015
FRom the abstract of the paper cited above:
We significantly improved the quality of our data for predicting putative orthologous genes and for generating data subsets by matrix reduction procedures, thereby improving the signal to noise ratio in the data. Eight different data sets were constructed, representing various combinations of orthologous genes, data subsets, and taxa. Our results demonstrate that the different ways to compile an initial data set of core orthologs and the selection of data subsets by matrix reduction can have marked effects on the reconstructed phylogenetic trees. Nonetheless, all eight data sets strongly support Pancrustacea with Remipedia as the sister group to Hexapoda.
So it would seem that unsteady eddie was wrong. It isn't circular reasoning at all. The point is that knowledge of evolutionary processes can help to remove noise form the data, thus improving the signal to noise ratio. It DOES NOT affect the overall result, which is robust with regard to such data manipulation.
KlausH said:
Actually, it has been pretty well established that Biblical unicorn was a rhinoceros, the leviathan was a crocodile, and the behemoth was a hippopotamus.
"pretty well established" -- that's hilarious.
mattdance18 · 30 January 2015
Meanwhile, has anyone been behind the paywall to read the article? I am really curious about the details of their Zygentoma+Pterygota and Siphonaptera+Mecoptera findings.
callahanpb · 30 January 2015
DanHolme said:
their interest wasn't really piqued until we mentioned some of the big bugs found in the coal mines near Bolsover. As the intro to the article points out, many people can't stand them, and the thought of a dragonfly with a four-foot wingspan or a six-foot millipede really caught their imaginations.
I admit I used to be really afraid of spiders, though even then I enjoyed watching them from a safe distance. Dragonflies never bothered me, and I remember pictures of the giant ones from an illustrated encyclopedia in my childhood. Except for the spider thing, arthropods have always seemed very neutral to me, not at all sinister or icky (of course, you don't want cockroaches in the house). They remind me of little robots, because of the hard exterior, and can often be very beautiful (butterflies, obviously, but all kinds of metallic and colorful beetles as well).
So maybe the introduction is appropriate most readers. I really don't mean to nitpick. I just sort of don't get people who have an "ick" feeling about insects--with occasional exceptions like spittlebugs (mildly gross), maggots, and parasitic wasp hatchlings.
callahanpb · 30 January 2015
tomh said:
KlausH said:
Actually, it has been pretty well established that Biblical unicorn was a rhinoceros, the leviathan was a crocodile, and the behemoth was a hippopotamus.
"pretty well established" -- that's hilarious.
At least we know the walrus was Paul.
John Harshman · 30 January 2015
callahanpb said:
tomh said:
KlausH said:
Actually, it has been pretty well established that Biblical unicorn was a rhinoceros, the leviathan was a crocodile, and the behemoth was a hippopotamus.
"pretty well established" -- that's hilarious.
At least we know the walrus was Paul.
Semolina pilchard on the road to Damascus?
DS · 30 January 2015
so booby, what organism should the scorpion fly be most like in its dna? if like looks means like dna, i guess it should be most like a scorpion, right? what about the fleas? is they should be mostly similarity wise likened to lices? what does a creationist model predict?
i don't like the idea of like equals like, dna or likewise other stuffs
John Harshman · 30 January 2015
mattdance18 said:
Why is the silverfish more similar to winged insects than to bristletails in terms of DNA, Robert?
Couple of problems here. First, "bristletail" is used for two different groups on the tree: Diplura ("two-pronged bristletails") and Archaeognatha ("jumping bristletails"); it's not a group, and the first isn't even considered part of Insecta.
Second, I don't actually know if the silverfish (which is by the way similar to referring to humans as "the mammal") is more similar to winged insects in terms of DNA. As I hope everyone knows, phylogenetic analysis doesn't run on raw similarity. That would require us to believe in an absolutely perfect molecular clock. It's the fit of the data to a tree with particular topology and branch lengths that counts. (The tree in the figure has been massaged to calibrate the branches to time, so it all comes out even; but I guarantee that the actual tree resulting from analysis had widely varying branch lengths.) It's fully possible that silverfish are more similar, in terms of raw sequence similarity, to one or more bristletail groups than to any winged insects.
mattdance18 · 30 January 2015
John Harshman said:mattdance18 said:
Why is the silverfish more similar to winged insects than to bristletails in terms of DNA, Robert?
Couple of problems here. First, "bristletail" is used for two different groups on the tree: Diplura ("two-pronged bristletails") and Archaeognatha ("jumping bristletails"); it's not a group, and the first isn't even considered part of Insecta.
Second, I don't actually know if the silverfish (which is by the way similar to referring to humans as "the mammal") is more similar to winged insects in terms of DNA. As I hope everyone knows, phylogenetic analysis doesn't run on raw similarity. That would require us to believe in an absolutely perfect molecular clock. It's the fit of the data to a tree with particular topology and branch lengths that counts. (The tree in the figure has been massaged to calibrate the branches to time, so it all comes out even; but I guarantee that the actual tree resulting from analysis had widely varying branch lengths.) It's fully possible that silverfish are more similar, in terms of raw sequence similarity, to one or more bristletail groups than to any winged insects.
Thanks for the clarifications, John. I hadn't realized that "bristletail" was part of a common name applied to Diplurans. I should've been more careful and said "Archaeognatha" instead. As for the second point, yes, I understand that as well, so I should probably be more careful in terms of how I'm parsing things. But I do hasten to add, in Robert's case, I don't exactly think more careful parsing would help him correct his misunderstanding; it's much more a gross failure than that.
harold · 30 January 2015
its cute about the 400 being corrected to 470m years. Why the previous failure??
Did anybody not see this coming?
I almost bothered to predict it as soon as I saw the fine tuning of the dates, but I figured if I predicted it I'd be accused of causing it.
mattdance18 said:
Thanks for the clarifications, John. I hadnât realized that âbristletailâ was part of a common name applied to Diplurans.
Neither had I. I've never seen that used anywhere other than the linked tree.
Reed A. Cartwright · 30 January 2015
I moved a bunch of comments to the BW. Let me know if I missed anything or sent something there that I should not have.
37 Comments
John Harshman · 29 January 2015
Unlike the bird paper, this one is paywalled. What's all this about silverfish losing their wings? And what's the evidence that they lost whatever independently of jumping bristletails?
mattdance18 · 29 January 2015
Quick question about the silverfish. The picture caption indicates that silverfish "lost their wings." Is there any evidence that they ever had wings? I thought that wings were one of the derived features of the Ptergygota, to whom the silverfish are the sister group.
The parallel losses of head endoskeleton, styli, and coxal vesicles seem to be implied by the tree, as the basalmost silverfish, Tricholepidion, still has them. But wing loss for the whole Zygentoma lineage, too? That would be news.
I ask because I am not a subscribe and therefore cannot access the article. Does it discuss this? Not trying to be snarky, just wanting clarification.
mattdance18 · 29 January 2015
callahanpb · 29 January 2015
Sorry if I sound like a complainer, but I didn't like the intro to this article. I think most people who would want to read the content are strongly in the camp of those who find insects fascinating and associate them with hours of childhood bug-watching.
Joe Felsenstein · 29 January 2015
The link for "partitioning scheme" leads to a page on partitioning hard disks. No doubt important, but probably not what was intended.
DS · 29 January 2015
I was pleased to see that the crustaceans are shown as the sister group to the insects. This is a relationship supported by the mitochondrial gene order data.
I was also pleased to see that this study confirmed the sister group relationship between the Siphonaptera (fleas) and Mecoptera (scorpionflies). I have done some work on the sperm morphology of hangingflies and this is what the sperm morphology also indicates. Common design it is not.
Soon the trolls will appear to claim that it is just a line of reasoning, or circular reasoning, or whatever. I will ask them in advance to explain the congruence of the molecular and sperm morphology data and the distinct lack of any common morphological similarities between the groups. If they cannot, then any pissing or moaning that they do can be safely ignored.
John Harshman · 29 January 2015
DS: Clarification. Crustacea isn't the sister group of the insects. Crustacea is paraphyletic to the insects, whose sister group is the remipedes.
mattdance18 · 29 January 2015
Robert Byers · 30 January 2015
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stevaroni · 30 January 2015
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Dave Luckett · 30 January 2015
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TomS · 30 January 2015
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DanHolme · 30 January 2015
DS · 30 January 2015
so booby, why is flea dna so similar to scorpion fly dna? is it like looks? if not answer then creation points disregarded as only line of reasoning with no biological evidences
KlausH · 30 January 2015
This comment has been moved to The Bathroom Wall.
TomS · 30 January 2015
DS · 30 January 2015
DS · 30 January 2015
DS · 30 January 2015
If anyone is interested, I did find this article about the remipedes:
http://decapoda.nhm.org/pdfs/38922/38922.pdf
DS · 30 January 2015
FRom the abstract of the paper cited above:
We significantly improved the quality of our data for predicting putative orthologous genes and for generating data subsets by matrix reduction procedures, thereby improving the signal to noise ratio in the data. Eight different data sets were constructed, representing various combinations of orthologous genes, data subsets, and taxa. Our results demonstrate that the different ways to compile an initial data set of core orthologs and the selection of data subsets by matrix reduction can have marked effects on the reconstructed phylogenetic trees. Nonetheless, all eight data sets strongly support Pancrustacea with Remipedia as the sister group to Hexapoda.
So it would seem that unsteady eddie was wrong. It isn't circular reasoning at all. The point is that knowledge of evolutionary processes can help to remove noise form the data, thus improving the signal to noise ratio. It DOES NOT affect the overall result, which is robust with regard to such data manipulation.
Scott F · 30 January 2015
This comment has been moved to The Bathroom Wall.
mattdance18 · 30 January 2015
This comment has been moved to The Bathroom Wall.
mattdance18 · 30 January 2015
Obviously, since "like looks equals like DNA," the two people pictured here:
http://www.newprophecy.net/George_W._Bush_and_lookalike_comic_Steve_Bridges-001.jpg
will be more genetically similar than the two people pictured here:
http://georgewbush-whitehouse.archives.gov/news/releases/2005/07/images/20050722-6_w9w7031jpg-515h.jpg
Right, Robert?
Can you see your ongoing error yet?
tomh · 30 January 2015
mattdance18 · 30 January 2015
Meanwhile, has anyone been behind the paywall to read the article? I am really curious about the details of their Zygentoma+Pterygota and Siphonaptera+Mecoptera findings.
callahanpb · 30 January 2015
callahanpb · 30 January 2015
John Harshman · 30 January 2015
DS · 30 January 2015
so booby, what organism should the scorpion fly be most like in its dna? if like looks means like dna, i guess it should be most like a scorpion, right? what about the fleas? is they should be mostly similarity wise likened to lices? what does a creationist model predict?
i don't like the idea of like equals like, dna or likewise other stuffs
John Harshman · 30 January 2015
mattdance18 · 30 January 2015
harold · 30 January 2015
harold · 30 January 2015
This comment has been moved to The Bathroom Wall.
TomS · 30 January 2015
This comment has been moved to The Bathroom Wall.
callahanpb · 30 January 2015
This comment has been moved to The Bathroom Wall.
John Harshman · 30 January 2015
Reed A. Cartwright · 30 January 2015
I moved a bunch of comments to the BW. Let me know if I missed anything or sent something there that I should not have.