I look like this some mornings before my first glass of OJ.

As ace reader Janice correctly guessed, the red velvety patches — really galls, or abnormal plant growths caused by the invasion of a parasitic organism — from the last post were created by a tiny erineum mite (Aceria sp.). I’ve seen many a gall in my time, and I *never* suspected that the scarlet patches were the product of gall-making critters. After several years of seeing these scarlet patches and having no bloomin’ idea what they were, I had to consult my old pathology of trees and shrubs professor (and author of “Magical Mushrooms, Mischievious Molds“) Dr. George Hudler, who clued me in.

So what might a mite be, anyway? Well, like the bio-faux pas of calling a mosasaur a dinosaur (Paleontologists: “It’s a marine reptile, d***it!”), never call a mite an insect. It’s a greatly evolved arachnid, like spiders, ticks and most scorpions (excepting the ones with power ballads). Most arachnids have eight legs, plus two pairs of special mouthparts called chelicerae and pedipalps. Mites, which properly include the ticks, are among the most successful invertebrates on earth, and are the only arachnids that have been found in Antarctica. Some are completely self-reliant. But because mites are (as their name accurately implies) so tiny, many others specialize in freeloading, which they have elevated to an art form. They cause mange (sarcoptic mange mites); they live in dust and cause allergies (dust mites); wreak destruction on colonies of honeybees (varroa mites); chew holes in, and cause untold agony among witless, unprepared southerners (chiggers); decimate house plants, including many of the prized specimens of this author (spider mites); and they frolic about your eyelashes, follicles, face, pores and skin, eating dead skin cells and sebum, going out for evening constitutionals on your sleeping face and, I’m sorry to reveal, making more mites (demodex mites).

And they make galls. Though not all plant galls are mite-induced (tiny gall wasps being the other major cause), many are. An entire family of mites, the Eryiophyidae, have adopted this lifestyle, and these galls can take on all sorts of fantastical forms and colors. Erineum mites have a few quirks; they have only two pairs of legs, for example, as you can see above. And they are REALLY tiny. without a dissecting microscope, you are unlikely to be able to see them, even with a hand lens, as they are only .05 to .2 mm long (i.e. 50 – 200 microns long! The spores of the fungus I published my first master’s thesis on where in that range!).

So how do erineum mites coax the plant into making those crazy galls? After overwintering on the tree, the females jump on young leaves and start feeding on the underside. Chemicals in their saliva stimulate the growth of the velvet patch, or erineum (pl. erinea, whence the mites get their name, though whether the scarlet pigment is mite-produced or mite-induced I have not been able to discover). Then they crawl inside. And guess what? The velvet patch is both maternity ward and love shack. That’s right: if this gall’s a rockin’ . . .

The good news for maples (Acer sp., the major target of the aptly named Aceria sp.), is that the galls rarely harm the tree. Instead, think of them as hip, festive forest decor. Without erineum gall, that copse of trees just has no “pop”. : )

To find these suckers in the tree of life, look for Eriophyoidea here, and back out by the arrow on the left to get a sense of where you are.

An additional source used in writing this post can be found here.

It’s a whip scorpion, in the order Thelyphonida, although this one has sadly somehow lost its long thin tail, or “whip” (called technically, like those of protists and sperm, a flagellum — but they are *not* evolutionarily-related structures). This one seems to be very well fed, though thankfully not on Jen. I’m taking a short arachnology class at the Denver Museum of Nature and Science right now, and this was one of our subjects. According to my classmate, these animals, also commonly called vinegarroons because of the defensive acetic acid (vinegar) glands they possess near their tails, are the nerds of the arachnid world: “They just kind of bumble along, smelling like a salad.” Raptoral pedipalps (big scary pincers) aside, the one I held did seem to be a sweet, gentle creature. I’ve now held a whip scorpion! Yay!

I haven’t talked about arthropods at this blog much yet, and a paper published in Nature a few weeks ago together with my play date with Stumpy, above,  provide the perfect opportunity to correct that. This post is called “The Creepy-Crawly Branch of the Family Tree”, but it could equally well be called the Floaty-Swimmy Branch, or the Bloody-Sucky Branch or the Borey-Eggs-Iny-that-Hatchy-and-Devour-the-Insides-of-your-Hosty Branch. There are arthropods that do all these things. So let’s have a look at the broad shape of the tree as revealed by this new analysis of the evolutionary relationships among members of Arthropoda:

Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences Jerome C. Regier, Jeffrey W. Shultz, Andreas Zwick, April Hussey, Bernard Ball, Regina Wetzer, Joel W. Martin & Clifford W. Cunningham Nature 463, 1079-1083(25 February 2010) doi:10.1038/nature08742

Now there are a lot of scary words on this diagram, it’s true. But take heart! Look how many drawings of awesome creatures there are! And it’s way better than the alternative that most biologists have to deal with, which I also had to learn to read in school. Before I get to what’s new and cool about this tree, let’s talk a little bit about what trees like this are, and then about the main groups you see on it.

This tree is called a phylogeny, or phylogram (you also hear cladogram). It is a hypothesis of evolutionary history. That doesn’t mean scientists are hypothesizing that these creatures evolved. That’s a foregone conclusion. The hypothesis is what the specific relationships are between the different groups. In other words, the question is, “How is everyone related?”, and this tree is one possible answer. In some trees, as appears to be the case here, the branch lengths are proportional to the evolutionary distance between the different groups. That is, the longer the branches, the more evolvin’ that’s been going on. Evolution, in this case, is measured in DNA nucleotide changes. DNA, as you’ll recall, is made of many base pairs called nucleotides. There are four kinds. When one changes to another, that is called a point mutation. The more of these changes that build up, the greater the evolutionary distance between groups.

For this tree, scientists studied 62 genes in 75 arthropod species. They sequenced them all and compared the changes. They put all the data into a special computer program designed to figure out which sequences are most similar to which other sequences in the five-jillion possible combinations of relationships embodied by 62 genes in 75 species. Then they cranked the computers up to 11 and probably waited a few days (or maybe even weeks! I have heard stories of scientists locking computers in closets during this time) for them to churn out the solution to this hyper-space chess problem. The lone tree you see above is the result.

So what do we see? At the top is Hexapoda, which as you may guess are insects and friends — the six-legged among us. Below them you see an interesting group called Xenocarida. More on them later. Below that group are the Vericrustacea and Oligostraca, which are both, as far as I can tell, basically crustaceans. In both groups you see some old friends: the copepods (some freshwater species of which carry Guinea Worm larvae, a topic I covered in January), the ostracods (who we looked at in a post on deep-sea bioluminscent organisms last year), and the Decapoda, which has a high taxonomic tastiness index: it includes lobsters, crayfish, crabs, and shrimp.

Next are the myriapods: centipedes and millipedes. Below that are the chelicerates, or organisms with special mouthparts called chelicerae — sea spiders (pynogonids), horseshoe crabs, scorpions, ticks, mites, tarantulas, spiders, and Stumpy. And rounding out the base of the tree are the outgroups — the groups we use to “root” the tree, or give it a direction. They are usually the most closely related organisms not in the group of interest, here arthropods. In this case, they are the ridiculously cutely-named water bears or moss piglets — the tardigrades — and velvet worms, the onychophorans. Velvet worms are half of the subject of a crazy-*** theory that somehow got published last year hypothesizing that metamorphosing insects like butterflies were the result of an unholy chimerical union between velvet worms and a larva-less insect.

Also looming large in the arthropods but not on the tree simply for reasons of chronological discrimination (and also because, being extinct, we have no DNA to sample) are the the trilobites. According to my copy of Colin Tudge’s Variety of Life, they branched off somewhere between the Tardigrades and Chelicerates.

OK, so now that you’ve waded through all of that, what were the surprises in this new tree? Scientists also used to think millipedes and centipedes were closely related to insects. They’re both land arthropods, after all. My two college biology texts (published 1995 and 1996) show this relationship, though Tudge(2000) is agnostic on whether millipedes and centipedes or crustaceans are more closely related to Insects. Now it appears certain that, since all crustaceans are aquatic, insects and centipedes/millipedes represent a seperate evolutionary invasion of land by arthropods, much as seals and whales represent two seperate re-invasions of the sea by mammals.

This study also supports the hypothesis that insects evolved from a crustacean, which is why we can’t use the term “Crustacea” any more — the group as traditonally defined doesn’t include the insects, but this tree shows that it should (since the principles of modern evolution-based taxonomy require proper groups to include an ancestor and ALL of its descendants). The term “Reptiles” poses the same dilemma, because it should technically include  birds. So some scientists have stopped using that term as a taxonomic classification, too. Little-r reptiles is OK, though, as informal name for the group.

Finally, it appears hexapods’ (insects’) closest relatives are an obscure underwater-cave-dwelling group newly dubbed the Xenocarida. Carl Zimmer goes into that in admirable detail here.

But the take-home message of this tree for you is simple: look, admire, and marvel at the variety and abundance. In fact, I give you a homework assignment, should you choose to accept it: pick a group on that tree that looks interesting that you’ve never heard of before. Look it up. Find out what it is, what it does for a living, and where it directs its mail. You’ll be glad you did, I promise.

. . . and she knows how to use them. The harvestman (daddy long legs) Phalangium opilio. Credit: Dschwen/Creative Commons Attribution Sharealike 2.5 License. Click for link.

Sometimes evolution moves quickly and groups of organisms change radically over very short spans of geologic time. Think of modern horses, which evolved from dog-sized creatures over the course of the last few tens of millions of years. Or take humans — we only evolved about 150,000 years ago, and if you look at our ancestors ca. 3 million years BP, you’d find yourself looking at an unfamiliar face indeed. But sometimes, when a particular organism hits on a successful niche, it changes hardly at all.

I’ve previously mentioned that sharks and mosses fall into this category. But this week I found an interesting story about some amazing harvestman fossils that show they are in the same boat. Harvestmen, also called daddy long legs, are arachnids like spiders or scorpions. Scientists recently found two new species in fossils from north central China that date from 165 million years ago. That’s right — the Jurassic, When Dinosaurs Ruled The Earth.

The two new species, described by Selden and his colleagues in an upcoming Naturwissenschaften, were entombed in fine-grained volcanic ash that fell in what is now north central China about 165 million years ago. The harvestmen — and the ash — either dropped into a lake or were washed there soon after the ash fell, Selden notes. Little is left of those ancient harvestmen: The fossils are, for the most part, 3-D outlines of fragile bodies that disappeared long ago. Those tiny molds, however, preserved even small details of the creatures, including their mouthparts, genitals and the joints of their legs.

You just gotta love German science journal names. Wait . . . genitals? Yes. According to scientist Paul Selden, one of the authors of the paper, the details are so fine and the organism so similar to existing harvestmen, we can tell that if you saw one of the fossilized species wander through your back yard today, you wouldn’t even look at it twice. And this is a creature that once may have scuttled underneath T. rex or Stegasaurus!

I can’t publish the photo here for copyright reasons, but head on over to Science News to see the fossil and read the rest of the article and make sure to embiggen that fossil photo — twice.  With enough time, it is amazing what low-probability events can happen.