madame scientist's not-so-mad musings

The Master Archer

▶ Lurking under the water surface in the estuaries and mangroves of India and Polynesia, the archer fish Toxotes (from the Greek Τοξοτης for archer) precisely aims a ballistic jet of water that knocks off a hapless insect from the shrubbery above, sending it tumbling into the water where it is promptly devoured. To dislodge prey anchored firmly to the vegetation with forces up to 10 times their body weight, the water jet must achieve a power of 3000 Watts/kg within a fraction of a second. Since this intrepid hunter was first described 250 years ago, scientists have puzzled over this mastery of archery.

▶ Fishy Physics: Biologists first considered a mechanism similar to the chameleon, where energy is stored in coils of collagen inside the tongue (explained in the Chameleon Catapult post http://goo.gl/B5fPVS). But dissection of the archer fish revealed no such specialized structure. Besides, they calculated that muscle power could maximally account for ~15% of the observed force of the water jet. Researchers then resorted to analysis of high speed video recordings of the archer fish in action. What they saw was a thin jet of water with a “head” that becomes increasingly bigger during flight. Surface tension and inertia hold the head together, pushing the tail jet into the head forming hammer-like pellet which strikes with deadly force. A fancy term for this is hydrodynamic amplification, and the physicists among you may enjoy reading about the “Ohnesorge number” and “Rayleigh-Plateu Instability” in the referenced paper. The rest of us will be intrigued by the similarity to Drop on Demand Inkjet Printing which similarly uses an explosively ejected drop of ink, as in Canon’s Bubble Jet printer (http://en.wikipedia.org/wiki/Inkjet_printing). The archer fish achieves all this at a low evolutionary cost by gulping a small amount of air into a gun-barrel shaped groove in its mouth and closing its gills before delivery. Just like Diana the huntress amplified her muscle power with a bow, this little fish also exploits an external hydrodynamic lever to capture its prey.

REF: Vailati et al. (2012)  PloS ONE; open access http://goo.gl/DHZ1C 

H/T to PJ Rosenberg for inspiring this post with the gif image he shared to the Science on Google+ community (http://goo.gl/fPDy2u).

#ScienceSunday  

Do You Like Green Eggs And Ham?

Yes, I like them, Sam-I-Am

White eggs, Brown eggs,  Pink ones too

But Tell me, how Do they turn Blue?

(With apologies to Dr. Seuss) 

♦ Egg color in birds evolved for obvious reasons of camouflage and recognition, and for less obvious reasons such as thermal regulation, protection against UV light, and even antimicrobial defense. Chicken eggs are commonly white (no pigment), or brown (protoporphyrin). Rare breeds from China and Chile lay blue eggs, colored by the bile pigment biliverdin, a breakdown product of the hemoglobin in red blood cells.  Biliverdin is normally excreted by liver cells into the bile. So how does it end up in the egg shell? 

♦ Organic anion transporters are proteins that move a large number of compounds- drugs, toxins, hormones and bile pigments, across cell membranes, as part of the liver’s detoxifying day job. Genetic sleuthing mapped the blue color trait to a region of a chicken chromosome. Here was a gene for a transporter protein, SLCO1B3, that could provide blue-green biliverdin to color the shell. But why was the gene inexplicably turned on only in the shell gland of the blue egg laying chicken?

♦ Endogenous retroviruses (ERV) are ancient viruses that inserted randomly into the genomes of prehistoric birds. One such viral fragment inserted right next to the SLCO1B3 gene in blue egg laying chickens, where it behaved like an accidental transcription enhancer, or “on switch”. Because of its sequence, scientists speculate that it mediates estrogen specific regulation, accounting for the high levels of the biliverdin transport protein in the shell gland. Although this story nicely explains our Seussian curiosity about green eggs and ham, it also shows how viruses shape diversity in the living world. For example, an insertion of the avian leukosis virus inside a gene for the enzyme tyrosinase results in white plumage in chickens. Viral insertions can also be incredibly harmful, triggering cancer when they accidentally turn on oncogenes.

REFS (open access papers): http://goo.gl/3yJ1FS and http://goo.gl/ypZyCF

Fun Fact: Green Eggs and Ham, published in 1960, is one of the best selling and most beloved children’s books of all time. It has just 50 words, and was written by Dr. Seuss in response to a bet by his publisher. 

Photo: Tammy Riojas, Elgin, TX;

H/T to Lorna Salgado for posting the news story that led to this   #ScienceSunday  post. 

Rattler!  Did you know that the western diamondback rattlesnake Crotalus atrox can rattle its tail continuously for hours at frequencies approaching 90 Hz (90 times per sec)? This is twice as fast as a hummingbird’s wings. 

● Nailing the Noise: The tail-end of the rattlesnake has a series of hollow “buttons” linked together, each made of keratin (found in our nails) and modified from the snake’s scales. At birth, there is only one pre-button, but each time a snake sheds its skin, another button emerges at the end. It’s a myth that one can tell the age of a rattlesnake from the number of buttons, because a snake may molt variably in a year and the buttons do break off with use.  

● Sound production in animals, is energetically expensive. But the rattler is an evolutionary marvel, optimized for minimal cost and maximal efficiency (for the aficionados, only 0.015 micromoles ATP consumed per gram muscle per twitch). Surprisingly, energy use is independent of temperature and rate of rattling. There are six sets of tailshaker muscles, arranged at 45 degree angles to the axis of the tail. All six are active during rattling, with muscles on one side contracting while those on the other side relax. This out of phase contraction generates an oscillating motion seen in the gif image. 

● Once you’ve heard a live rattler, you’ll never forget it, says Gnotic Pasta, who has plenty of snake stories to share. Do you have any cool facts or anecdotes about rattlers? Also check out Buddhini Samarasinghe scary post on Bite Reflex of a Snake here: http://goo.gl/Lz7oBN

▶ BBC Video (3:50 min) on high speed filming of the rattle (look behind the rattle for the forked tongue darting out!): Slow motion rattlesnake – Slo Mo #3 – Earth Unplugged

▶ Great basin rattlesnake Crotalus viridis lutosus filmed by our intrepid G plusser Gnotic Pasta  :  http://vimeo.com/64675533

▶ REF (old, but free): Structural correlates of speed and endurance in skeletal muscle: the rattlesnake tailshaker muscle. Schaeffer et al. http://jeb.biologists.org/content/199/2/351.long

H/T to Amy Robinson Sterling  for sharing the gif that inspired this post (http://goo.gl/pzi4Yv). 

#ScienceSunday