Getting ready for Darwin Day

You should mark your calendars now…oh, wait, you’re all godless neodarwinist stooges, so you’ve already got Darwin Day colored in with circles and arrows and hearts. OK, so you should add an annotation if you live somewhere near Minneapolis, because the Bell Museum is sponsoring a special Darwin Day Cafe Scientifique, which will combine art and science to tell the story of evolution.

LIFE: A Journey Through Time
North American Premiere /Darwin Day Opening Event
Thursday, February 12, 2009, 7 to 9 p.m.
Bell Museum Auditorium
$10/ free to museum members and University students

Celebrate the 200th anniversary of Charles Darwin’s birthday with a special preview of LIFE: A Journey Through Time. The event will feature top University biologists using Lanting’s photographs as a springboard to deliver a rapid-fire presentations relating their research on evolution to the images. From the big bang to the human genome, hear the newest theories on how life evolved and enjoy the North American premiere of one the world’s most celebrated photography exhibits. Think speed-dating – Darwin-style!

This event is also the premier of an exhibit of a stunning collection of nature photography. You should go to that, too.

LIFE: A Journey Through Time
February 14 – April 12, 2009

The University of Minnesota Bell Museum of Natural History is proud to host the North American premier of this internationally acclaimed exhibit. LIFE: A Journey Through Time, interprets the evolution of life on Earth through photographer Frans Lanting. Lanting’s lyrical photos trace Earth’s history from the beginnings of primordial life to the ascent of mammals through otherworldly landscapes and breathtakingly intimate portraits of animals and plants engaged in million-year-old rituals. Many of the exhibit’s 62 photographs are matched with real animal, fossil, and plant specimens from the Bell Museum’s collection. Born in the Netherlands, Lanting serves on the National Council of the World Wildlife Fund and is a columnist for Outdoor Photographer and has received the BBC Wildlife Magazine’s Wildlife Photographer of the Year Award and the Sierra Club’s Ansel Adams Award for Conservation Photography.

One other special feature is that the speakers (I’m one of them) are going to present in Pecha Kucha style. This could be interesting, too.

Pecha Kucha (usually pronounced in three syllables like “peh-chach-ka”) was started in Tokyo, Japan in February 2003 by Astrid Klein and Mark Dytham as a designers’ show and tell event to attract more people to SuperDeluxe, their multi-media experimental event space they had set up in Roppongi.

The idea behind Pecha Kucha is to keep presentations concise, the interest level up and to have many presenters sharing their ideas within the course of one night. Therefore the 20×20 Pecha Kucha format was created: each presenter is allowed a slideshow of 20 images, each shown for 20 seconds. This results in a total presentation time of 6 minutes 40 seconds on a stage before the next presenter is up.

I’m planning to talk about the evolution of multicellularity…with 20 slides in 6 minutes and 40 seconds. We’ll see how that goes.

Chemical replicators

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We’re one step closer to self-sustaining chemical replicators, similar to what would have existed a few billion years ago, before true cells evolved. Lincoln and Joyce have created a couple of relatively simple molecules that assemble themselves from even simpler precursors in a test tube.

It’s not as straightforward as the simplest scheme one might imagine. The simplest model would be for a single enzyme, E, to catalyze its own assembly from two smaller precursors, A and B. This formula would lead to a test tube full of A and B to be quickly converted to a test tube full of nearly nothing but E with the introduction of a single copy of E. The actual solution is a little more difficult to explain.

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Ancient spiders

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Spiders are amazingly sophisticated animals, and probably the premiere complex adaptation of modern spiders is the ability to spin silk. They have multiple internal glands that can produce multiple kinds of silk — webs contain different kinds, from structural strands to adhesive strands, and other kinds are used for spinning egg cases and for wrapping prey — and they are sprayed out through small spigots mounted on swiveling spinnerets, which are modified opisthosomal (abdominal) limbs. Obviously, these detailed features did not spontaneously appear all at once, but had to have evolved progressively. A couple of fossils have recently been described that reveal a) silk spinning is ancient, from at least the Permian, but that b) these early spiders did not have the full array of modern adaptations.

Here is a pair of fossils: Permarachne novokshonovi, from the Permian in Russia, and a more recent specimen, and Palaeothele montceauensis, from the Carboniferous in France. Both are eight-legged arthropods, and if you saw one scuttling about now you wouldn’t hesitate to call them spiders. There are some differences, though: Permarachne in particular shows a little less tagmosis, or fusion and specialization of segments, than we usually see in spiders, and it also has that prominent flagellum (which is completely different from a bacterial flagellum!), a long segmented ‘tail’ covered with sensory hairs that was probably a sense organ; it has no sign of a web-spinning function.

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(Click for larger image)
Paleozoic Araneae and Uraraneida. (A-C) Permarachne novokshonovi, Permian of Russia, PIN 4909/12. (A) Holotype part in rock matrix. (B) Explanatory drawing of A. (C) Close-up of flagellum showing whorls of setae. ch, chelicera; cx, coxa; fe, femur; mt, metatarsus; pa, patella; pl, ventral
plate; st, sternum; ta, tarsus; ti, tibia. (D) Palaeothele montceauensis, Carboniferous of France, In 62050a, X-ray CT scan showing appendages buried in the rock matrix; note, anal tubercle (arrowed)
is not a flagellum. (Scale bars: B, 1 mm; C and D, 0.1 mm.)

What about the production of silk and webs in these old spiders? Here’s another specimen, Attercopus fimbriunguis, a 376 million year old fossil. It’s a little less dramatic because these are fragments of cuticle that have been carefully extracted by dissolving the rocky matrix with acid; it means, unfortunately, that it is more fragmented, but the advantage is that now we can zoom in microscopically and see far more detail in the structure. What we can now see in pieces of the ventral plates of the opisthosoma are small spigots, and in a few cases, there are even strands of spider silk still extended from these pores. In F, there’s also a nice shot of a chelicera (fang) from the spider — it’s wicked sharp, but the small holes seem to be preservation artifacts, and there’s no sign that venom secretion, another important spider adaptation, has evolved yet.

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(Click for larger image)
Attercopus fimbriunguis, Devonian of New York (localities: G, Gilboa; SM, South Mountain), macerated from matrix with HF and slide-mounted. (A) First-described “spinneret,” G 334.1b.34; darkness of cuticle reflects number of layers, so this fragment is folded over
twice. (B) Palpal femur, SM 1.11.12; arrow indicates patch of distinctive spinules. (C) Piece of cuticle from corner of opisthosomal ventral plate showing setae, spigots, and possible silk strand, SM 1.11.4.
(D) Close-up of E showing possible silk strand emerging from spigot shaft, SM 1.11.4. (E) Flagellar structure with 12 segments (including possible distalmost) from original Gilboa locality; segments show distal
collars and setae, G 334.1a.4. (F) Close-up of cheliceral fang showing a number of holes (arrowed), the most distal of which had been interpreted as a venom-gland
opening, G 329.22.9. (Scale bars: 0.5 mm, except F, 0.25 mm.)

One of the critical observations here is very simple: no spinnerets. These spiders did not have the modified limbs with sets of spigots that we see nowadays, but instead, had a series of spigots arrayed across the bottom of the abdomen. They almost certainly were not able to make webs: what they could have done was produce sheets of silk, of the kind that could be used to make egg cases or wrap around prey. These are another example of a transitional fossil, forms that have only some of the capabilities of a later organism.

(via Cheshire, who promises to have his own post on this paper soon.)

Selden PA, Shear WA, Sutton MD (2008) Fossil evidence for the origin of spider spinnerets, and a proposed arachnid order. Proc Nat Acad Sci USA 105(52):20781-20785.

Evolutionary gems

This week, Nature magazine published a short list of recent important developments in evolutionary biology that support the theory of evolution, as a tool to help explain that evolution is definitely a dynamic and useful theory in our field and to demonstrate that the evidence is still growing. Here’s a short summary of the 15 stories the editors picked out, but you should also read the freely available article, 15 Evolutionary Gems. Teachers, put this in your classroom!

  1. The discovery of Indohyus, an ancestor to whales.

  2. The discovery of Tiktaalik, an ancestor to tetrapods.

  3. The origin of feathers revealed in creatures like Epidexipteryx.

  4. The evolution of patterning mechanisms in teeth.

  5. The developmental and evolutionary origin of the vertebrate skeleton.

  6. Speciation driven indirectly by selection in sticklebacks.

  7. Selection for longer-legged lizards in Caribbean island populations.

  8. A co-evolutionary arms race between Daphnia and its parasites.

  9. Non-random dispersal and gene flow in populations of great tits.

  10. Maintenance of polymorphisms in populations of guppies.

  11. Contingency in the evolution of pharyngeal jaws in the moray.

  12. Developmental genes that regulate the shape of beaks in Darwin’s finches.

  13. Evolution of regulatory genes that specify wing spots in Drosophila.

  14. Evolution of toxin resistance.

  15. The concept of evolutionary capacitance: the idea that environmental stress can expose hidden variations that are then subject to selection.

For those who think human bones would make a great gift

Here’s an interesting new blog, Moneduloides, that seems to have an emphasis on human evolution, if you’re into that sort of thing, and it currently has a short list of good texts for Christmas presents. <moan> I’ve done absolutely no Christmas shopping at all this year, so if the economy tanks and my family hates me, it is all my fault. I just have to get out from under this stack of grading first.

Amylase and human evolution

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I made a mistake that was quickly corrected by a correspondent. Yesterday, in writing about copy number variants in human genes, I used the example of the amylase gene on chromosome 1, which exists in variable numbers of copies in human populations, and my offhand remark was that the effect is “nothing that we can detect”, but that maybe people with extra copies would be “especially good at breaking down french fries”. Well, it turns out that we can detect this, that there was even a very cool study of this enzyme published last year, and that the ability to break down complex starches rapidly may have been a significant factor in human evolution.

So of course I have to tell you all about this now.

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Copy Number Variants are not evidence of design

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The Institute for Creation Research has a charming little magazine called “Acts & Facts” that prints examples of their “research” — which usually means misreading some scientific paper and distorting it to make a fallacious case for a literal interpretation of the bible. Here’s a classic example: Chimps and People Show ‘Architectural’ Genetic Design, by Brian Thomas, M.S. (Note: this is not the peer-reviewed research paper implied by the logo to the left — that comes later.) The paper is a weird gloss on recent work on CNVs, or copy number variants. Mr Thomas makes a standard creationist inference that I have to hold up for public ridicule.

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