May 7, 1998
Science. "How Male Animals Gain
an Edge in the Mating Game."
Article by Elizabeth Pennisi
Summary by Deependra Chhabra
During the summer '97, some 600 biologists gathered at the University
of Maryland for the annual meeting of the American Behavior Society.
Among the many talks included discussions of the lengths male animals
have gone to find a mate.
We have all heard of the mating calls of a bullfrog. The call has long
been thought to radiate from the large vocal sac that bulges from under
the frog's chin. But new studies by Alejandre Purgue, who studies
animal acoustics at the University of California, has traced it to a
different part of a bullfrogs anatomy: its ears. He found that the ears
acted as loudspeakers, amplifying the sounds of the frogs vocal cords.
Purgue discovered this unexpected use for bullfrog's eardrums while
trying to pin down how frogs use their vocal cords. He designed a
sound-generating device that could be placed inside frog's mouth that
could provide a reproductive sound for each test. He then turned it on
to see how various body part amplified it. He was surprised to find that
much of the stronger responses come from the eardrums. The measurement
implies that frogs not only hear but also call, through their ears.
There ears account for 70 to 80 percent of the total sound output.
Male bowers win females by dancing on and around their bowers-
platforms or towers made of sticks. It has been believed that the males
impressed the females by demonstrating their architectural prowess. But
evolutionary biologist Gerald Borgia of University of Maryland, reported
that they serve a different purpose. The bowers can provide a screen,
allowing the dancing and preening to be more vigorous without
frightening the females. He said that certain bowers have evolved in
certain ways to allow males to display in a more energetic fashion.
Thus the male spotted bowerbird makes an unusually wide bower with
see-through straw walls and approaches the females from behind them.
Extensive studies of a common insect pest, the Indian meal moth are now
showing scientist, how males can change the size of adult body parts to
optimize their sperms chances of success. Matthew Gage from the
University of Liverpool in United Kingdom raised larvae in jars. He had
jar with one, five, 10 and 20 larvae adjusting the food amounts
accordingly. When the larvae emerged as adults, they were the same size
but proportioned differently. Those who lived alone had small tested
and produced less sperm. They had larger heads and thoraxes. This was
because they had to face less competition and produce less sperm in
order to reproduce. They used their energy to produce other body parts
and also live longer. On the other hand the moths that live in jars
with competition had large testes. They had small body part because
most of their energy was spent in producing sperm. These insects also
tended to die sooner than their counterparts in uncrowned jars.
Elizabeth Pennisi (18 July 1997). How Male Animals Gain an Edge in the
Mating Game. Science. Vol.277, pp.317-318.