Transitional Species in Insect Evolution

In "On the Origin of Species" Charles Darwin listed as one of the gravest objections to his theory the apparent paucity of intermediate or transitional forms, which he attributed (at least in part) to the imperfection of the fossil record. Well over a century later this is still being raised as an objection to evolutionary theory but such objections are increasingly misinformed as a growing number of transitional species, both living and fossil, have been found. Transitional species in the evolution of various vertebrate groups (several of which have a surprisingly good fossil record) have been discussed on the web. Recent molecular studies, combined with some truly exciting fossil discoveries, have illuminated the origins of several major kinds of animals from previously existing groups: tetrapods (4-legged land-dwelling vertebrates) from fish, birds from dinosaurs, and whales from artiodactyls (land-dwelling hoofed mammals with 4 legs) (for more information see the Transitional Vertebrate Fossils FAQ and 29+ Evidences for Macroevolution at Talk Origins). These new discoveries have largely supported hypotheses of evolutionary relationships that were previously based on morphological and other evidence, but provide a much more vivid picture of the evolution of these groups that had previously been largely hypothetical, in many cases providing concrete and compelling fossils of intermediate or transitional species between the major groups.

Similar transitions can be found in invertebrate groups such as insects. Although the origin of insects, the largest group of animals on earth, is still unclear (current evidence suggests they evolved directly from crustaceans) they have left a good fossil record during their subsequent evolution. The evolution of insects is discussed in a recent book titled, appropriately enough, Evolution of the Insects by entomologists David Grimaldi and Michael Engel. If you have any interest in insects and their evolution, this is the book for you. This is a very big and very heavy book, but it is also extremely well-illustrated with both fossils and living insects. The authors present the current state of knowledge of insect evolution as known from morphological, molecular, and fossil evidence. Grimaldi's specialty is fossil insects, particularly those preserved in amber, and the book is abundantly illustrated with diagrams and photographs of fossils, of extinct insects, and of living insects. Detailed phylogenies of all the major groups are presented, with detailed discussion of the evidence upon which those phylogenies are based. The writing is clear and not excessively technical; it should be accessible to anybody with some knowledge of basic biology and/or entomology. One of the most fascinating things I discovered in this book is that current data strongly indicate that several of the distinct, well-defined, and traditionally recognized insect orders have evolved directly from within other existing orders. Examples are Siphonaptera (fleas) from Mecoptera (scorpionflies), true lice (Phthiraptera) from the order containing barklice and booklice (Psocoptera) (with chewing lice providing a transition to sucking lice), and termites (Isoptera) from cockroaches (Blattaria). It is this last transition that I will discuss here.

The differences between cockroaches and termites are dramatic. Cockroaches are more or less omnivorous detritivores and scavengers (as witnessed by the success of several species as household pests) whereas termites eat wood, digesting its cellulose with the aid of symbiotic bacteria and protists. Cockroaches are generally solitary; termites form huge colonies of related individuals founded by a long-lived "queen" and "king". Cockroaches vary little within a species (aside from age and sexual differences); termites have a marked differentiation into winged reproductive and unwinged non-reproductive "castes" (e.g., workers and soldiers). Cockroaches have 2 pairs of wings that are different and are retained through their adult life; termites have 2 pairs of wings that are similar ("isopterous") that are shed after mating. Cockroaches and termites are as well-defined and distinct as any two orders of insects; in colloquial terms they can be considered entirely different kinds of insects. Yet there is now compelling evidence that one of these "kinds"--termites--has evolved directly from the other--cockroaches. This conclusion is both surprising and unsurprising: unsurprising in that termites have always been acknowledged on the basis of internal and external morphology to have some relationship to cockroaches and other orthopteroid orders. What is surprising, beyond the obvious differences between termites and cockroaches, is that termites have evolved from a group within the order Blattaria, and in fact are more closely related to one particular living genus of cockroaches than that genus is to all other cockroaches. In other words, termites ARE cockroaches, albeit highly modified due to their specialized lifestyle that differs from that of their ancestors.

If termites have indeed evolved from cockroaches, then we should expect to find transitional living or fossil termite-like cockroaches and cockroach-like termites. In addition, other lines of evidence should be consistent with this relationships. For example, the derived taxa (termites) should not predate their ancestors (cockroaches) in the fossil record. Moreover, the earliest members of the derived group--that is, the ones closest to the evolutionary divergence--should be the most similar to the ancestral group. Finally, the phylogenetic relationships of their symbiotic bacteria and protists, which are utterly dependent upon their hosts for survival, should be similar to the phylogenetic relationships of their hosts.

Cryptocercus, a termite-like cockroach

While termites have generally been accepted as being related to other "orthopteroid" orders, different hypotheses had argued for their closest relationship being with either cockroaches or mantids. However, on the basis of morphology and other evidence some authors have suggested a particularly close relationship between one termites and a living genus of cockroaches, Cryptercercus. While typical cockroaches in many ways, the nine species of Cryptocercus share numerous characteristics with termites.

Termite-like characteristics of Cryptocercus:

* exhibit social behavior
* live and nest exclusively in dead wood
* eat and digest wood with the aid of endosymbiotic bacteria and protists
* harbor several genera of symbiotic protists found in termites but not other cockroaches
* live long and pair monogamously (most cockroaches short-lived, mate promiscuously)
* provide parental care for nymphs
* nymphs fed by anal secretions of the adults
* symbiotic protists and bacteria passed to nymphs in anal secretions
* nymphs strikingly termite-like in appearance




Cryptocercus punctulatus adult with nymphs (from Origins of Termites)


Mastotermes, a cockroach-like termite

Are there also termites that retain cockroach-like characteristics? Yes. The Australian "giant termite" Mastotermes darwiniensis, which has long been considered one of the most primitive termites, shares several characteristics with cockroaches that are not found in other termites.

Cockroach-like characteristics of Mastotermes:

* large size (other termites are much smaller)
* expanded pronotum ("shield" on the first thoracic segment, reduced in other termites)
* hind wings with an expanded anal fan (absent in other termites)
* ovipositor present (absent in all other termites)
* eggs laid in oothecae (clusters in a membrane-enclosed capsule; other termites lay solitary eggs)
* feet with 5 tarsal segments (all other termites have 4)
* harbor endosymbiotic bacterium Blattabacterium, a genus found in cockroaches but not other termites



Mastotermes darwiniensis, a cockroach-like termite (from Evolution of Insects)



Mastotermes darwiniensis, female reproductive after shedding wings (from Tree of Life)



Mastotermes darwiniensis nymphs, workers and soldier (from Termites as Structural Pests)

Evolution of termites from cockroaches

The molecular, morphological, behavioral and endosymbiont data show that the evolution of termites from cockroaches, while seemingly rapid in geological terms, has gone through several stages, with "typical" termite characteristics being acquired stepwise:

Stage 1: primitive roaches with long ovipositors (earliest roach-like fossils);
Stage 2: ovipositor shortened; typical cockroaches (plenty of those still around);
Stage 3: wood-dwelling cockroaches that mate monogamously, care for their nymphs, and can eat and digest wood. (Represented by the living genus Crytocercus);
Stage 4: development of a true social lifestyle with a caste system consisting of a reproductive "queen" and "king" and sexually suppressed nymphs differentiated into non-reproductive workers and soldiers; acquisition of some "typical" termite characteristics (e.g., forewings membranous and wings shed after mating). (Represented by the living genus Mastotermes);
Stage 5: acquisition of more typical termite characteristics (e.g., ovipositor lost, eggs laid singly, hing wings lose their anal fan, all 4 wings "isopterous"); represented by all other living termites.

Note that the genus Cryptocercus can NOT be considered directly ancestral to termites, as it has specializations of its own (e.g., loss of wings). This is to be expected as the lineage leading to Cryptocercus has had a long evolutionary history of its own since it diverged from the common ancestor with termites, and continued to evolve independently after that divergence. However, the termite-like characteristics of Cryptocercus and cockroach-like characteristics of Mastotermes demonstrate that evolution of termites from cockroaches has been relatively gradual, has occurred stepwise by a progressive loss of cockroach characteristics and accumulation of termite characteristics, and has left evidence of this evolution in the surviving descendants of at least two transitional species that occurred along the way.

Fossil record

Grimaldi & Engel place the first appearance of true cockroaches in the fossil record as early Cretaceous, and termites at about the same time. Although appearing at about the same time in the fossil record, the Cretaceous termite fossils belong to the primitive (although still extant) families Mastotermitidae, Hodotermitidae, and Termopsidae. However, the earliest cockroach fossils are already diverse and represent several modern families, suggesting a much earlier origin and evolutionary divergence. This earlier origin is also suggested by "roachoid" fossils that occur from the Carboniferous into the Jurassic. Although it is often claimed that cockroaches first appeared in the Paleozoic era in more or less modern form and have changed little since, these early "roaches", dubbed "roachoids" by Grimaldi, while similar to cockroaches general appearance and sharing many characters with them, differ in having elongate ovipositors more like those found in the closely related order Orthoptera, rather than the reduced ovipositors of cockroaches (and Mastotermes)--in other words, they comprise an entirely different set of transitional species between primitive orthopterans and true cockroaches. Some of these "roachoid" fossils are so roachlike that the difference is little more than semantic, and there can be little doubt that modern cockroaches evolved directly from one of the "roachoid" lineages sometime during the Jurassic. The discovery of trace fossils interpreted as termite nests in the early Jurassic also suggests that the evolution of both true cockroaches and termites may have occurred considerably earlier than the Cretaceous although this is consistent with both the appearance of diverse cockroach and termite body fossils in the early Cretaceous, as well as the occurrence of "roachoid" fossils into the Jurassic.



A Carboniferous "roachoid" (from LARGEST FOSSIL COCKROACH FOUND)


Molecular evidence

Molecular phylogenies have supported morphological and other evidence (e.g., social behavior) in showing that Cryptocercus is more closely related to termites than it is to other cockroaches, and that Mastotermes is primitive with respect to all other termites. An interesting test of the phylogenetic relationships between cockroaches and termites is the phylogenetic relationships of their symbionts. As stated above, there is a strongly suggestive overlap of symbiotic protists and bacteria between cockroaches, Cryptocercus, Mastotermes, and other termites. These bacteria and protists are incapable of living apart from their hosts, and are passed from one generation of hosts to the next via anal secretions. Their utter dependence upon their hosts means that they have evolved in parallel with their hosts, and indeed the molecular phylogenies of the symbionts have proven to almost perfectly parallel the host phylogeny: the symbionts of Mastotermes and other termites are most closely related, are next most closely related to the symbionts of Cryptocercus, and are next most closely related to those of other cockroaches.

Summary

1. Cryptocercus is a cockroach with social characteristics of termites.
2. Cryptocercus shares endosymbionts with termites that are not shared with other cockroaches.
3. Molecular evidence shows that Cryptocercus is more closely related to termites than it is to other cockroaches.
4. Molecular evidence shows that the endosymbionts of Cryptocercus are more closely related to those of termites than to those of other cockroaches.
5. Mastotermes is a termite with numerous morphological characteristics of cockroaches that are not shared with other termites.
6. Mastotermes shares certain endosymbionts with cockroaches that are not found in other termites.
6. Molecular evidence shows that Mastotermes is primitive with respect to other termites.
7. The oldest termite fossils belong to Mastotermitidae and other primitive families.

Creationists might make the typical claim that "Cryptocercus is still just a cockroach, and Mastotermes is just a termite" but this would be a gross oversimplification that conveniently ignores the evidence. It does not address why Cryptocercus has so many termite-like characteristics, and Mastotermes has so many cockroach-like characteristics, when the molecular evidence indicates that Cryptocercus is the closest living relative of termites, that Mastotermes is the most primitive living termite, and even the relationships of their endosymbionts support this relationship. In other words, the data from several different kinds of evidence point toward the conclusion that termites evolved directly from cockroaches. Taken individually these data could be argued or interpreted in different ways; taken together they point to the unavoidable conclusion that, as Grimaldi says in a review of insect evolution, "Termites are highly modified, social, myopic, wood-eating roaches."

References available on the web (in no particular order):

Colony composition, social behavior and some ecological characteristics of the Korean wood-feeding cockroach (Cryptocercus kyebangensis)

Origins of Termites

Termites and trees: a review of recent advances in termite phylogenetics

Evidence from multiple gene sequences indicates that termites evolved from wood-feeding cockroaches

Phylogeny of Mantodea based on molecular data: evolution of a charismatic predator (supports paraphyly of roaches with respect to termites)

Mantophasmatodea and phylogeny of the lower neopterous insects

Insect evolutionary history from Handlirsch to Hennig, and beyond

Evidence for Cocladogenesis Between Diverse Dictyopteran Lineages and Their Intracellular Endosymbionts

Advanced early Jurassic termite (Insecta: Isoptera) nests: evidence from the Clarens Formation in the Tuli Basin, southern Africa.

The Garden in Winter

Winter is always a bit depressing for a gardener, but even more so for those of us who grow tropical plants. It has stayed cold and the snow we got over a week ago still hasn't melted yet. Here's a view of the back yard from a second floor window taken last weekend; looking at this photo I realize that one thing I need to work on is planting more evergreens so the garden will not be so dead and depressing all winter (note that the fatsia is about the only thing still green in the lower garden; redtip and aucubas are still green at the top of the hill near the garage):



Compare this to how the same view looked back in August:



Oddly enough, Isabella loves the snow. Here she is romping in the garden; remains of my hardy banana (Musa basjoo) are in the middle and on the right you can see my hardy windmill palms, which incredibly enough made it through last winter:



Here's a closeup of the palms, looking beautiful and green against the snow (although they won't look quite this nice by March):



BRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR!

So here's to warmer times past and future, a shot of my hardy banana in August:

A Cat's-Eye View of the BNA Holiday Party

I'm getting this out rather late (which seems to be becoming a pattern of my blogging) but Dan's company holiday party was as always a nice chance to get dressed up, eat some good food, enjoy some drinks and chat with Dan's co-workers. Dan works with a great bunch of people at BNA and as it turns out, they've all read this blog and LOVE the entries by Isabella. Funny, I haven't gotten nearly as much feedback on my own entries!

This was supposed to be another guest blog by Isabella, but she expressed no interest whatsoever in doing it. She's always a bit miffed when we go somewhere without her. Not that she wants to come along; rather, she just wants us to stay home all the time and worship her. Or it could be because she smelled fish on me but I didn't bring any home for her. Or maybe it was the photos. Since she couldn't go (and even if she didn't want to go, she still would have appreciated the invitation--maybe that was teh problem) I had to promise to take some photos for her, so of course I thought I would take some photos that a cat would appreciate. She took one look at them and didn't say anything, but from the look on her face I could tell she was thinking, "I've always suspected you're mildly retarded and of course you've proven me right." Oh well, even if she didn't appreciate all the trouble I went to for her, here they are:













The guys all thought it was pretty funny. Little did they know I would go after their wives. Or maybe they dared me to. I can't remember, I did have a glass of wine or two. So I went to track down the ladies. I'm sure they all thought I was either drunk or crazy.



Sometimes I even had to be a bit sneaky about it:












Whether it was the wine or that I was by now drunk with power, by this point I was apparently photographing everything that looked even vaguely like a foot with a shoe on it:



Sorry Isabella, I'll do better next time and take the photos you really wanted to see. I know how much you like to lick people's ears...

APOCALYPSE SNOW

Okay, I know the title is a bad pun (all right, it's not a pun at all because "now" and "snow" aren't even similar in pronunciation) but the fact is, in Washington an inch of snow is considered the First Horseman of the Apocalypse (with four or more inches making up the entire apocalyptic posse). Whenever as little as a half inch of snow is forecast, you'd think nuclear armageddon was upon us because the entire region goes crazy. People stampede the grocery stores to buy bread, milk, toilet paper, diapers, you name it, apparently because they expect to be trapped in their houses for at least a month. Folks, this is NOT New Orleans and the dikes ARE NOT BREACHING. Last night we got maybe an inch of snow and a bit of freezing rain but as of 7:30 am the sun was shining, the snow and ice were melting, and all the roads were clear. But of course all the schools were closed, the city and federal governments opened two hours late (with an unscheduled leave policy, meaning you can just stay home if you want although it does come out of your annual leave), and our visiting friend David's 8 am flight to Portland out of National Airport was cancelled. I guess stories like this one make them antsy. Heck, I'm surprised they didn't shut down the entire airport for the entire day.

Well (and you knew it was coming), I grew up in Buffalo, NY and we were HAPPY to get an inch of snow because it meant we didn't have to go out and shovel two FEET of snow from the driveway, and then have to go to school anyway. So when it snows in Washington I just sit back and enjoy the show.

WATCH THIS BLOG

I haven't been blogging lately and now I know for a fact that people who blog regularly have no lives away from their computers. But WATCH THIS SPACE for these exciting blog entries:

Isabella's Review of the BNA holiday party WITH PICTURES
"Happy holidays" vs. "merry Christmas"
Transitional Species in Insect Evolution
An Archeological Dig Through My Life

On The Intelligent Design Of Mice (guest blogging by Isabella)

I know my daddies are smart, but sometimes they do things that just aren't very intelligent. Like leaving me home alone all day. Well of course I sometimes get in trouble. Helloooo? I'm home alone without supervision and I'm bored! What do they expect? I have no idea what they could possibly be doing when they're not home with me. It must be terribly important for it to take them away from ME because I'm the most important thing in their lives. I know it's true because of all the special things they do just for me!

One thing I like about my daddies is when they make toys for me. They make something they call a "mouse" which is a little toy covered with fur and stuffed with catnip, pointy at one end and with a little tail sticking out the other. Everything fits together so well! Without the catnip it wouldn't be nearly as much fun, and without the fur it would all fall apart. And without the tail... well, without the tail it just wouldn't be a mouse, would it? Sometimes they give the mouse to me, and sometimes they put it where they know I will find it while they're gone. They're so much fun to play with but they don't last very long. Every time I chew one up they make me another one. I don't know how they make them, or what they make them out of, because I've never seen them do it. I don't ask too many questions because I'm just so happy they keep making them for me. (And besides, if my daddies don't make them, where could the mouses possibly be coming from? They're no good for anything except me playing with them.)

Well, a few weeks ago they really outdid themselves. I found a new mouse under the sofa. I didn't see them put it there, but I know they left it there just for me. There isn't anybody else in this house they could possibly have made it for! But this one was different from all the others they ever made for me. I always had to bat the old ones around myself, but this one MOVED. And not from somebody pulling it on a string either (I checked); it moved all on its own! It didn't have any catnip in it, but it smelled delicious in a completely different way. I don't know how they did it, but they figured out how to make something that smells even better than catnip. They're so clever! It was just about perfect and I could tell everything about it was made JUST for me, smell and all. It had eyes and ears, so it see and hear me and run away from me, and it was SO much fun to chase around the house! It had a cute little tail like the others, but whenever I touched the tail of this one, it jumped and tried to run away! But best of all, when I played with it, it made the most delicious little squeaking noises! How did they know this was EXACTLY what I wanted when I didn't even know it myself! It was even better than the cicadas they made for me last year, and those were so much fun. I guess all they needed was a little practice. My daddies do surprise me sometimes, and that's one of the things I love about them.

The biggest problem with the old mouses was that eventually they just fall apart. First the tail comes off, then their fur gets icky after I slobber all over them, the catnip loses its smell, and they come apart at the seams and the catnip starts leaking out (and it doesn't even taste good). I thought they might fix some of those problems with the new model, but this one didn't last even one night. First it stopped running around, and then it stopped squeaking. I kept poking it and batting it around, hoping it would start working again, but it was no use, it was broken. I was so sad. It was the very best gift they EVER made for me, and I broke it. I left it in the middle of the living room rug so they would see it and make me a new one. I saw them pick it up the next morning and they looked quite concerned about it. I don't think they realized it would break so quickly. I guess they still need more practice making toys. I know they'll make me a new one but they must not be easy to make because it's already been a few weeks and I'm still waiting. If they think the stick-under-the-newspaper game is going to keep me entertained, they'd better think again.

Oops, gotta go! I think I hear the stick!

Isabella