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Nabokov and Evolution

Carl Zimmer has a wonderful article at the New York Times on the confirmation of Vladimir Nabokov's once-ridiculed idea about the evolution of his favorite group of butterflies, the Polyomattus blues. In 1945, when Nabokov published his idea that the butterflies had made their way from Asia, across the Bering Strait, and down to Chile in five different waves, there was no way to test his hypothesis. Today, thanks to research methods built on the discovery in 1953 of the structure of DNA, it's possible to construct evolutionary trees by isolating and comparing genes from closely related organisms. And that's just what a team led by Naomi Pierce at Harvard has done with these beautiful insects. Zimmer's article explains why their findings confirm Nabokov's hypothesis.

Pierce's team used some of the most advanced tools available to biologists. But their research fundamentally relies on Nabokov's painstaking efforts to develop an accurate classification of the different species within the group--classifications that the team re-examined and found reliable. To me, this is an example of the most interesting kind of biological research: the melding of advanced investigation of molecules with old-fashioned close and patient observation of organisms, both fueled by passionate creativity.

Zimmer's blog post has links to his Times article, to the Pierce paper, and to Nabokov's monograph. Read More 
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David Pogue on Spider Silk's Strength Follow-Up

Here's an excerpt of David Pogue's Making Stuff: Stronger episode, taken from the PBS News Hour:



Later in the episode, Randy Lewis gives a nifty explanation of dragline silk protein's strength using Legos, springs, and zippers. If you want to learn more about how such an extraordinary material has evolved, read Chapter 6 in Spider Silk. And if you get a chance to catch the whole episode in future, it's well worth your time.  Read More 
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David Pogue on Spider Silk's Strength

CBS News has a preview of David Pogue's spider silk segment on his new Nova: Making Stuff series on PBS. This should be fun. I'm interested to see whether Randy Lewis or any other spider silk experts get a chance to explain why copying spiders' ability to make silk in the quantities we desire is so difficult.  Read More 
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Coyne on the BSC

We wrote Spider Silk for two reasons. First, we wanted to share the wonders of spider silk and reveal how it allows spiders to take advantage of their surroundings in surprising ways. But second, we believe spiders and spider silk can show nonbiologists, in concrete detail, how the theory of evolution explains the mind-boggling variety of living beings on Earth.

We found Jerry Coyne and H. Allen Orr's book Speciation invaluable as we wrestled with how best to present some of this information. For nonbiologists, the questions of what exactly defines a species and how species become and remain distinct from each other are often perplexing--just as they were for Charles Darwin and Alfred Russel Wallace before they independently arrived at their brilliant insight. Yesterday and today, over at his Why Evolution Is True site, Coyne explains why the "biological species concept" (BSC) is the most useful way to think about species:

"What is the origin of species? Under the BSC, that question becomes equivalent to 'What is the origin of reproductive isolating barriers between closely related species?' And that is a much more tractable question."

Highly recommended reading: Part 1 and Part 2Read More 
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BBC Wildlife Magazine and SB&F Like Spider Silk

In my experience working with third graders, they all love to get star stickers on their work. I'm not sure what this says about our psychosocial development, but so do we: we just got 6, plus some nice comments, and we're floating. The American Association for the Advancement of Science's Science Books and Film awarded us two out of two stars, and the BBC Wildlife Magazine gave us four out of five (five stars indicates "a classic," and we are first-timers, so we're not disappointed we didn't get full marks). To read excerpts from the reviews, please go to our press/links tab.

And if you want to spread the good cheer contained in these reviews, consider this: Spider Silk makes the perfect gift if you celebrate Christmas, and celebrate it with a Christmas tree. One legend has it that a poor family couldn't afford tree decorations. A spider they had treated gently spun silk all up and down the tree as they slept the night before Christmas. When the sun streaming through the window the next morning hit the threads of silk, they turned into silver. And, supposedly, this explains why people strew tinsel on their trees.  Read More 
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Venomous Mesotheles

If we're fortunate enough eventually to write a second edition of Spider Silk, we'll have to make a change: contrary to what we wrote, we now know that mesothele spiders do have venom glands.

Mesotheles are the oldest branch of the spider evolutionary tree. Arachnologists consider them "living fossils": these spiders remain outwardly virtually identical to a 290-million-year-old mesothele fossil found in France, so their characteristics and behaviors can provide insight about spiders' early evolutionary history. They share a common ancestor with the much more numerous mygalomorphs (tarantulas and their closest relatives) and araneomorphs (the "true spiders" most of us are more likely to come into contact with), which in turn share a more recent common ancestor that they don't share with the mesotheles. Mesotheles are difficult to study. They live only in Asia, they're hard to find, and they're long-lived, which means any researcher wanting to study their life cycle has to be awfully patient.

With the exception of the araneomorph family Uloboridae, (which clearly lost them during evolution) all other spiders have venom glands. So whether or not mesotheles also have them is an important spider evolution question, especially as researchers work to figure out how spiders first evolved along a different path from their closest arachnid relatives. Depending on the answer, researchers would look for the origins of the venom glands in one of two different time spans. If the mesotheles don't have venom glands, it probably means that this characteristic evolved after the original mesotheles but before the mygalomorph and araneomorph lineages diverged, between about 300 million years ago and 250 million years ago. But if all three major branches of the spider evolutionary tree (mesotheles, mygalomorphs, and araneomorphs) have venom glands, it means that the common ancestor of all the spiders probably also had venom glands. This common ancestor lived in its burrow at least 300 million years ago, and perhaps even more than 350 million years ago. (A third possibility, that the common ancestor of all spiders had venom glands but the mesotheles lost theirs during evolution, has usually been considered much less likely than these other two possibilities.)

The best single source of information on mesotheles is Joachim Haupt's 2003 monograph. In his studies, Haupt couldn't find either venom glands or the duct openings in the fangs that would indicate the presence of glands.

But now Rainer Foelix (author of the standard text Biology of Spiders) and Bruno Erb report in the latest issue of the Journal of Arachnology that they have indeed found such openings in nine different mesothele species by using stronger magnification. It wasn't easy. The openings measure only 5 to 10 micrometers in diameter (about the same size as a single red blood cell), and they lie not at the tip of the fang, where they would be easier to locate, but along its length. Having found the opening, Foelix and Erb were pretty sure they would find the gland, but this also proved challenging. Their description of how they had to tease out individual muscle fibers with watchmaker's forceps in order to expose the gland makes performing root canal look easy.  Read More 
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Talking Bugs

Dr. George McGavin and BBC Wildlife Magazine features editor Ben Hoare and staff writer James Fair have a fun and illuminating talk about insects, spiders, and other arthropods, as well as evolution, habitat loss, insects as food, and something I hadn't heard of and hope never to encounter, terrestrial leeches. About a third of the way through, listen for a nice mention of Spider Silk. Read More 
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Potter Wasps

As you know if you've read Spider Silk, spiders' most voracious predators are wasps. Over at Jerry Coyne's Why Evolution Is True blog, Matthew Cobb has an illuminating post about potter wasps. Potter wasps don't prey on spiders; they prefer caterpillars. But like araneophagic wasps, they guarantee their young get their meals in an ultra-fresh state: mother wasps sting and paralyze caterpillars and stock them live in the nests where they lay their eggs. The growing wasp larvae chew through prey that's not yet perished.

The core of Cobb's post is his explanation, based on a 1978 paper by Andrew P. Smith, of the decision-making process the wasp goes through as it builds the fortress and feeding chamber for its offspring. Experiments and observations of the type Cobb outlines give us tremendous insight into many of the behaviors of minute organisms--including spiders--that at first seem inexplicably complex.

Cobb first wrote this post for Pestival, the insect arts festival, which I hope is coming to a venue near you soon. Read More 
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Spider Silk Cited

Milestone: An academic paper has cited Spider Silk. We wrote Spider Silk for nonscientists, and it's been gratifying to receive reviews praising our book as "conversational," "easy to read," and "difficult to put down." But it's also great to know that other biologists recognize the validity of the science supporting our narrative. Although spiders make and use silk in unique ways, many other arthropods also use silk for various purposes. Miki Kanazawa, Ken Sahara, and Yutaka Saito of Hokkaido University in Japan have discovered that female Stigmaeopsis longus, a species of social spider mites, use silk threads to clean their communal nests. If you're interested in what it might be like to live in a highly humid, capsule-like nest with tens of others of your kind, the eye-opening introduction to their paper gives a glimpse of some of the grittier aspects. But of course, if you were this self-regarding co-author, the true frisson would kick in at footnote #27.  Read More 
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Touching

A new paper on how assassin bugs play on the web strings of spiders to lure them to their untimely end got a lot of publicity this week for good reason: "aggressive mimicry," in which a predator imitates something (for example, prey or a potential mate) that its prey is instinctively primed to approach, is intriguing on a number of counts. The paper, by Anne Wignall and Phillip Taylor of Macquarie University in Australia, details experiments they conducted to discover how the araneophagic Stenolemus bituberus tricks spiders into coming along the web to have a closer look. Mark Kinver at the BBC, Duncan Geere at Wired Science, and Jennifer Viegas at Discovery News all have good summaries.

But these summaries all focus on the assassin bug and its remarkably skillful underhandedness. I can't help but focus on the spider. Read More 
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