That’s some tongue

Behold the spectacularly long-tongued glossophagine nectar bat, Anoura fistulata:

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Anoura fistulata feeding from a test tube filled with sugared water; its tongue (pink) can extend to 150% of body length.

This length of tongue is unusual for the genus, and there is an explanation for how it can fit all of that into its mouth: it doesn’t. The base of the tongue has been carried back deep into the chest in a pocket of epithelium, and is actually rooted in the animal’s chest.

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Ventral view of A. fistulata, showing tongue (pink), glossal tube and tongue retractor muscle (blue), and skeletal elements (white).

Across the glossophagine nectar bats, maximum tongue extension is tightly correlated with the length of their rostral components, such as the palate and mandible. Although the correlation holds for A. caudifer and A. geoffroyi, A. fistulata falls far outside the 95% confidence interval. Close examination of tongue morphology reveals the basis for this pattern. In other nectar bats, the base of the tongue coincides with the base of the oral cavity (the typical condition for mammals), but in A. fistulata the tongue passes back through the neck and into the thoracic cavity. This portion is surrounded by a sleeve of tissue, or glossal tube, which follows the ventral surface of the trachea back and positions the base of the tongue between the heart and the sternum.

Unsurprisingly, this adaptation co-evolved with the lengthening corolla of a tropical flower, Centropogon nigricans—observations suggest that this bat is the only pollinator of this particular flower.

I’m sure Gene Simmons would be jealous.

Muchhala N (2006) Nectar bat stows huge tongue in its rib cage. Nature 444:701-702.

Animations of urogenital development

I found these on youtube, a couple of nice cartoony animations of the development of the urogenital system. This is one of the weirder modules in organogenesis, I think; many strange things go on that are relics of ancestral states. We actually build three pairs of kidneys—pronephros, mesonephros, and metanephros—and throw each one away in succession, except the last. Both sexes form paramesonephric (or Müllerian) ducts, in blue in the animation, and these form the core of the female plumbing, but again, males basically throw it away and use a more primitive duct (the mesonephric or Wolffian ducts, in green). It’s a bizarre way to construct an organ, but what’s going on is that we have two systems, excretion and reproduction, tied together in ways that constrain the other’s development, and each is building on elements of the other.

It’s in French, but that shouldn’t slow anyone down. It’s easy to figure out what “paramesonephrique” must refer to, for instance.

Males:

Females:

The Cambrian as an evolutionary exemplar

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I’ve been reading Valentine’s On the Origin of Phyla(amzn/b&n/abe/pwll) lately, and I have to tell you, it’s a hard slog. This is one of those extremely information-dense science texts that rather gracelessly hammers you with the data and difficult concepts on page after page. I am convinced that James W. Valentine is ten times smarter than I am and knows ten thousand times as much, and it’s a struggle to squeeze that volume of knowledge into my miniscule brain pan.

One thing I would like to greatly condense and simplify is his discussion of the Cambrian ‘explosion’. Misinterpretation of the Cambrian is one of the many prongs of the creationist assault on science; both old school Biblical creationists and the new stealth creationists of the ID movement have seized upon it as evidence of an abrupt creation—that a Designer poofed the precursors to all modern forms into existence suddenly, and without precursors, and that this observation contradicts evolutionary theory.

It doesn’t. Valentine has an excellent diagram that shows how wrong the creationists are.

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MADS boxes, flower development, and evolution

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I’ve been writing a fair amount about early pattern formation in animals lately, so to do penance for my zoocentric bias, I thought I’d say a little bit about homeotic genes in plants. Homeotic genes are genes that, when mutated, can transform one body part into another—probably the best known example is antennapedia in Drosophila, which turns the fly’s antenna into a leg.

Plants also have homeotic genes, and here is a little review of flower anatomy to remind everyone of what ‘body parts’ we’re going to be talking about. The problem I’ll be pursuing is how four different, broadly defined regions of the flower develop, and what that tells us about their evolution.

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The eye as a contingent, diverse, complex product of evolutionary processes

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Ian Musgrave has just posted an excellent article on the poor design of the vertebrate eye compared to the cephalopod eye; it’s very thorough, and explains how the clumsy organization of the eye clearly indicates that it is the product of an evolutionary process rather than of any kind of intelligent design. A while back, Russ Fernald of Stanford University published a fine review of eye evolution that summarizes another part of the evolution argument: it’s not just that the eye has awkward ‘design’ features that are best explained by contingent and developmental processes, but that the diversity of eyes found in the animal kingdom share deep elements that link them together as the product of common descent. If all we had to go on was suboptimal design, one could argue for an Incompetent Designer who slapped together various eyes in different ways as an exercise in whimsy (strangely enough, though, this is not the kind of designer IDists want to propose)…but the diversity we do see reveals a notable historical pattern of constraint.

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The sea urchin genome

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Oh happy day, the Sea Urchin Genome Project has reached fruition with the publication of the full sequence in last week’s issue of Science. This news has been all over the web, I know, so I’m late in getting my two cents in, but hey, I had a busy weekend, and and I had to spend a fair amount of time actually reading the papers. They didn’t just publish one mega-paper, but they had a whole section on Strongylocentrotus purpuratus, with a genomics mega-paper and articles on ecology and paleogenomics and the immune system and the transcriptome, and even a big poster of highlights of sea urchin research (but strangely, very little on echinoderm development). It was a good soaking in echinodermiana.

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A summary of the MnCSE Science Education Saturday

My day was spent in the Twin Cities attending the inaugural public meeting of the Minnesota Citizens for Science Education (MnCSE), and I can safely say now that Science Education Saturday was a phenomenal success: a good turnout, two top-notch talks, a stimulating panel discussion, and an involved audience that asked lots of good questions. You should have been there! I expect that, with the good response we got today, that there will be future opportunities to attend MnCSE events.

I’ll just give a brief summary of the main points from the two talks today. I understand that outlines or perhaps even the powerpoint files will be available on the MnCSE page at some future date, but give the organizers a little time to recover from all the effort they put into this meeting.

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