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08/07/2003
Potpourri of Bugs and Fish
With microbursts, power outages and now monsoon conditions
here in Jersey, I’m not up to tackling any deep subjects such as
black holes or multiple universes. (Yesterday, my wife and I
thought we might have to bail out of her car and swim for it, our
town’s streets were so flooded in a sudden cloudburst.) Hence
this week’s column consists of a potpourri of miscellany, some
relating to subjects of earlier columns. For example, in one
recent column, I discussed the romantic escapades of certain
dung beetles.
However, I didn’t touch upon the preparation and transport of the
dung in that column. Let’s rectify that omission by considering
one species of African dung beetle. Typically, he starts scouting
for dung in the evening when the sun is about ready to set. When
he finds a sample, he shapes some into a ball and moves the ball
in a straight line towards his home base. That way he gets home
in the fastest time, avoiding those who might filch the tasty
morsel and perhaps surprising any other male beetle making
advances to his spouse(s). Surprisingly, the beetle continues the
straight line even after darkness has set in.
Marie Dacke and her colleagues at the University of Lund in
Sweden, together with workers in South Africa, studied the
beetle and published their results in a recent issue of Nature. (I
haven’t seen the Nature article but found mention of it in the
Newscripts feature by K. M. Reese in the July 21 issue of
Chemical and Engineering News). It turns out the beetle only
continues on its linear path on a moonlit night. If it’s cloudy or if
there is no moon, the beetle’s path is erratic. There’s about a
million times less light than when the sun is shining. But it isn’t
just the moonlight; it’s the polarization of that light that the
beetles follow. The researchers put a polarizing filter over the
beetle. The filter shifts the polarization of the moonlight by 90
degrees and, sure enough, the beetle makes a right angle turn.
Various animals use the polarization of sunlight to navigate but
the dung beetle is the first found to navigate by moonlight.
Reese also mentions a situation that has a familiar ring to it. In
many areas of the U.S., there is an increasing problem with deer
and moving vehicles. The JR West Railway in Japan has the
same problem. According to an article by Kohtaro Matsuo in the
June 15 Asabi Daily news, the railway had 869 accidents
involving deer last year. What to do? Well, if you’ve had
problems with deer eating your trees and shrubs, have you tried
applying some lion dung?
That was one approach tried by JR West. They procured a
couple hundred pounds of the stuff from a zoo, diluted it and
spread it on roughly a quarter-mile section of a track linking a
couple of mountain stations. There were no deer hits on the dung
section but there have been 13 hits on the rest of the track. The
railway also tried a less odiferous approach. One of their
employees, a hunter, had heard that hunters shouldn’t wear white
clothing because deer don’t cotton to the color white. So they
strung white Styrofoam bars on a rope along the tracks and,
although no statistics were given, an engineer who had
experienced numerous deer hits previously said the results were
spectacular. This sounds like a work in progress.
Enough about dung and such. Are you familiar with the word
“gynogen”? I wasn’t until I read a very brief item by Jennifer
Steinberg Holland in the August issue of National Geographic. It
seems that both the Amazon molly and the desert grassland
whiptail lizard are gynogens. The Amazon molly is a fish found
in southwestern U.S. and Mexico. What is peculiar about a
gynogen? It only comes in the female variety. The molly’s eggs
only give rise to female clones. You’ve probably spotted the
problem – there are no male Amazons! You might conclude that
these gals reproduce on their own, having no males with which
to mate.
However, there are a couple of closely related species of fish that
behave in a more normal fashion and the Amazons are quite
willing to get together with the males of those species. Indeed,
the Amazons have to mate in order to start their reproductive
process going. It seems that the male’s sperm merely serves as a
catalyst to start the embryos on their way. None of the male’s
DNA gets transmitted to the offspring. This would appear to be
a wasted effort for the male. However, mating with those
Amazons somehow makes the male more desirable to the
females of its own species. Strange indeed! Or is it? Sometimes
it seems that females of our own species are more impressed by
males with a reputation for getting along well with other women?
In the “good old days” (a truly sexist phrase), the wife was
expected to stay at home, tend to the children and serve good
meals to the lord of the house upon his returns from work. Those
days may be long gone, but not for the male zeus bug. The July
25 issue of Science reports on the zeus bug studies of Goran
Arnqvist of the University of Uppsala in Sweden and his
colleagues Theresa Jones and Mark Elgar at the University of
Melbourne in Australia. Do you notice a trend here? Swedish
researchers seem to enjoy collaborating with workers in the
Southern Hemisphere countries such as South Africa and
Australia. I suspect a ploy to get away from those long dark
Scandinavian winters, especially when the subjects are dung and
a tiny bug found on Australia’s east coast.
When I went on the Internet to find out more about the zeus bug,
I found that the researchers’ work had made the headlines all
over the world. The male zeus bug is variously described as the
ultimate male chauvinist or as the luckiest bug in the world.
Typically, in the animal world (our own species included), the
male tends to court the female by offering various inducements
ranging from dinners at fancy restaurants to baubles or displays
of male prowess. But not the male zeus bug, which is already
somewhat unusual in that it belongs to the class of bugs that can
walk on water, skimming up insects or other food items.
What intrigued the Scandinavian and Aussie workers was the
male zeus bug’s habit of hitching a piggyback ride on a female’s
back. The male zeus doesn’t just hop on and off her back but
may hang on for a week or more. OK, there’s some sex involved
but this apparently is a relatively quick affair and some males
hop on board even before the female is mature. It would seem
that the female could easily shake off her hitchhiker, only half
her size. The researchers decided to look more closely and found
that, where the male’s head is positioned, the female’s back has
some kind of unusual gland.
Was the female was being the ultimate wife, cooking up gourmet
meals for her spouse? To find out, the researchers fed the female
fruit flies labeled with radioactive tracers. The male was soon
setting off the Geiger counters himself. He was sponging off the
wife all along, dining on a waxy protein-rich substance delivered
from this gland. Some of the males were removed from the
backs of the females after mating. These males only lived half as
long as those who stayed on board. On the other hand, the
females didn’t produce any more or any fewer eggs when the
males were removed. There was no obvious benefit.
What does the female get out of all this? She’s already done
more than her share, producing the eggs, feeding her spouse and
carrying him around, possibly for the whole period of her
reproductive life. All these activities take energy. The workers
don’t know the answer but Elgar is quoted on a University of
Melbourne Web site as speculating that the female might have to
expend more energy if she throws out her suitor, only to have
another one or even a bunch of other males try to jump on. She
may just want to avoid the harassment and possible injury. Did I
mention the male zeus is only a millimeter long – he can’t eat too
much! As for the male, hey, free food and lodging, free transport
plus a bit of sex. How good can it get?
Allen F. Bortrum
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