Dr. Bortrum
04/02/2009
Butterfly and Asteroid Intruders
This has been a hectic two weeks filled with all kinds of medical tests and doctor visits in preparation for my wife’s knee replacement surgery yesterday and my own, hopefully in-and-out hernia surgery next week. Hence the following potpourri of easily understood subjects that don’t tax my feeble brain. (My wife’s knee replacement went well and now the long and demanding recovery and physical therapy begin.)
First, a note concerning our mention of the International Year of Astronomy, which marks the 400th anniversary of Galileo pointing his telescope skyward at the moon in 1609. According to a brief item by Eliza Strickland in the April issue of Discover magazine, we should really be celebrating Thomas Harriot, who beat Galileo to the punch almost four months earlier that year. Over the following years, Harriot made detailed maps of the moon but never published them. Speculation is that Harriot’s wealthy patrons had been imprisoned in the Tower of London and perhaps he and/or the patrons were concerned about keeping their heads attached to their bodies should he publish anything smacking of controversy!
There seems to be no question about this year being the 200th anniversary of Charles Darwin’s birth. Fittingly, we discussed an example of evolution in the case of a particular kind of katydid, which learned to mimic the sound of a female cicada replying to a male cicada’s call for dalliance. In the case of the katydid, the object was to lure the male cicada close enough to ensnare him for a meal. Last week I came across another case of mimicking in the insect world with a less deadly outcome.
Until I read an article by Francesca Barbero and colleagues in the February 6 issue of Science, I hadn’t considered that ants were a noisy bunch of insects. However, and I quote from the article concerning ants: "...the adults in 4 of the 11 subfamilies stridulate by scraping a plectrum located on an anterior segment of the abdomen (post-petiole) across a file (pars stridens) on the first segment of the gaster." I’m ashamed to say that there is more than one word in that quote that required me to go to the dictionary. To avoid total disgrace, I won’t say which one(s) but will point out the key word "stridulate", meaning, according to my dictionary, "to make a shrill grating or chirping sound by rubbing certain body parts together."
Barbero and her coworkers in Italy and the UK have measured the sounds produced by the ant species Myrmica schenki, a type of ant found in Western Europe. They find distinct differences in the sounds produced by the queens as compared to the sounds produced by the worker ants. Now an ants nest is apparently a pretty lush place to live if you’re one of the some 10 thousand different species of critters that worm their way into the nests and feed as social parasites. One of these social parasites is the butterfly, Maculinea rebeli.
Foraging ants feed on plants harboring the butterfly larvae, which the ants carry back into their nest. These larvae beg for food in a way that resembles ant larvae begging for food and the ants feed the butterfly larvae, which later hatch into pupae. Some of the chemicals produced in the butterfly larvae and pupae mimic those of the ant larvae, which accounts for the successful deception that prompts the worker ants to feed them. Not only do the worker ants feed the imposters but the ants treat the butterfly larvae and pupae like they were queens; this is the behavior that intrigued Barbero and her team.
As you may have guessed, the answer proposed by the researchers is that the butterfly larvae and pupae produce sounds that are more like the queen ant than the worker ant. The paper contains graphs of the acoustical signals as well as pictures of the sound-producing organs of the ants and butterfly larvae and pupae. One thing I noted is that the queen’s sounds are at frequencies of around 800 Hertz (cycles per second), while the worker ant’s emit sounds in the 1100 Hz range. The butterfly pupae and larvae sounds are roughly in the 400 to 530 Hz range, closer to the queen’s than the worker’s frequencies.
The deceived workers do give the butterfly pupae and larvae extra attention, as they do the queen ant. The queen ant isn’t happy with these guys competing for her attention and behaves in a hostile manner to both the butterfly pupae and larvae, recognizing them as rivals.
On a different note, I’ve written a number of times about the fact that we should be more concerned about objects falling from the sky. Just a few weeks ago, there was that asteroid flyby, a mere 40 thousand miles away from our planet. That’s scary! An article by Andrew Grant in the April Discover magazine is about another object or objects that didn’t fly by but crashed into Earth only about 1500 years ago, in 536 A.D. Accounts at the time mentioned a "dark sun" and a fog that persisted over Europe for 18 months, ruining crops. Evidence that a comet or comets were responsible has been found by Dallas Abbott at Columbia University and her colleagues. They looked at Arctic ice cores dating back to that time and the cores contain carbon spheres, which can form due to heat and pressure of a cosmic impact.
Another report, this one from Douglas Kennett at the University of Oregon and his colleagues found microscopic diamonds in sediments dating back some 13 thousand years. The diamonds were found in sediments ranging across the continent of North America, in what has been termed the "black mat". Such tiny diamonds are an indication of severe heat and pressure, a signature of meteoric impact. Mammoth fossils have been found below this "black mat", but not above the "mat". This raises the possibility that the mammoths were wiped out, like the dinosaurs, by a cosmic intruder.
To complete our falling-from-the-sky theme, last week’s March 26 Star-Ledger had an AP article by Seth Borenstein on the finding in the Sudan of nearly nine pounds of rocks that made it to Earth from the asteroid 2008 TC3, which was actually tracked last year as it fell through the atmosphere. I went on the NASA Web site and found photos taken from a satellite of the meteorite exploding as it fell into the Nubian Desert in Sudan. There are also photos of Peter Jenniskens and University of Khartoum students, who fanned out in the desert searching for and finding those fragments of the fallen asteroid.
A NASA press release dated March 25 says that the asteroid was SUV-sized when it entered our atmosphere at 27,700 miles per hour and that it exploded 121,000 feet from the ground. The chances of finding any chunks of the asteroid were small, since these asteroids are relatively fragile. However, armed with a map based on the tracking data, Jenniskens, Professor Muawia Shaddad and students and staff from the University set out on December 6 last year and found 15 fragments weighing a little over a pound. Since then they gone back twice and picked up some 280 pieces weighing about 11 pounds. The rocks are very black in color and porous.
Scientists are delighted with this first-ever finding of pieces of something tracked before entering Earth’s atmosphere (they tracked it for 20 hours). In the Ledger article the asteroid was described as "non-threatening". Looking at pictures of some of the pieces, I would not call it non-threatening if you got hit by one! And, what did they find inside the asteroid fragments? Minuscule diamonds, of course.
The finding of this tracked asteroid is a boon to scientists who have been hoping for years to get a space probe to an asteroid and retrieve samples for analysis back here on Earth. Now they have samples of an asteroid and know where it came from. The belief is that this was a rock from space left over from the time billions of years ago when other rocks were busy forming planets, but this one didn’t make it. Sometimes you’ve got to be lucky. And, hey, whether we’re celebrating Galileo or Harriot, the International Year of Astronomy is off to a great start.
Next column April 16 or before, assuming our medical stuff continues on schedule.
Allen F. Bortrum
