belgareth
01-24-2006, 05:59 AM
I wonder if this also relates to us humans? :run:
Size Does Matter in Bats' Evolution By WILLIAM KATES, Associated Press Writer
Tue Jan 24, 2006
SYRACUSE, N.Y. - For some male bats, sexual prowess comes with a
price — smaller brains. A research team led by Syracuse University biologist Scott Pitnick found that in bat species
where the females are promiscuous, the males boasting the largest testicles also had the smallest brains.
Conversely, where the females were faithful, the males had smaller testes and larger brains.
"It turns out size does matter," said Pitnick, whose findings were
published in December in "Proceedings of the Royal Society: Biological Science," an online
journal.
The study offers evidence that males — at least in some
species — make an evolutionary trade-off between intelligence and sexual prowess, said David Hoskens, a biologist at
the Centre for Ecology and Conservation at the University of Exeter in England and a leading authority on bats'
mating behavior.
"Bats invest an enormous amount in testis, and the
investment has to come from somewhere. There are no free lunches," said Hoskens, who did not participate in the
study.
The relationship between the breeding system and relative
brain size has received little investigation, said Pitnick, who teaches evolution and population biology and
researches topics such as sexual selection and sexual conflict.
Bats
are the second largest group of mammals (behind rodents) with about 1,000 known species. Because of their
exceptional navigational and flying abilities, bats have been the subject of countless studies, providing Pitnick
and his colleagues — Kate Jones of Columbia University and Gerald Wilkinson of the University of Maryland — with a
bounty of data without having to slink off into caves.
Pitnick's
team looked at 334 species of bats and found a convincing contrast in testes size. In species with monogamous
females, males had testes starting at 0.11 percent of their body weight and ranging up to 1.4 percent. But in
species where the females had a large number of mates, Pitnick found testes ranged from 0.6 percent to 8.5 percent
of the males' mass (in the Rafinesque's big-eared bat).
"If female
bats mate with more than one male, a sperm competition begins," Pitnick said. "The male who ejaculates the greatest
number of sperm wins the game, and hence many bats have evolved outrageously big
testes."
Promiscuity is known to make a difference in testicle size
in some other mammals. For example, chimpanzees are promiscuous and have testicles that are many times larger than
those of gorillas, in which a single dominant male has exclusive access to a harem of
females.
Large brains, meanwhile, are metabolically costly to develop
and maintain. Pitnick's research suggested that in those bat species with promiscuous females, the male's body
used more of its energy to enhance the testes — giving it the greater adaptive advantage — and lacked the energy it
needed to further develop the brain.
The study found that in more
monogamous species, the average male brain size was about 2.6 percent of body weight, while in promiscuous species,
the average size dipped to 1.9 percent.
___
Size Does Matter in Bats' Evolution By WILLIAM KATES, Associated Press Writer
Tue Jan 24, 2006
SYRACUSE, N.Y. - For some male bats, sexual prowess comes with a
price — smaller brains. A research team led by Syracuse University biologist Scott Pitnick found that in bat species
where the females are promiscuous, the males boasting the largest testicles also had the smallest brains.
Conversely, where the females were faithful, the males had smaller testes and larger brains.
"It turns out size does matter," said Pitnick, whose findings were
published in December in "Proceedings of the Royal Society: Biological Science," an online
journal.
The study offers evidence that males — at least in some
species — make an evolutionary trade-off between intelligence and sexual prowess, said David Hoskens, a biologist at
the Centre for Ecology and Conservation at the University of Exeter in England and a leading authority on bats'
mating behavior.
"Bats invest an enormous amount in testis, and the
investment has to come from somewhere. There are no free lunches," said Hoskens, who did not participate in the
study.
The relationship between the breeding system and relative
brain size has received little investigation, said Pitnick, who teaches evolution and population biology and
researches topics such as sexual selection and sexual conflict.
Bats
are the second largest group of mammals (behind rodents) with about 1,000 known species. Because of their
exceptional navigational and flying abilities, bats have been the subject of countless studies, providing Pitnick
and his colleagues — Kate Jones of Columbia University and Gerald Wilkinson of the University of Maryland — with a
bounty of data without having to slink off into caves.
Pitnick's
team looked at 334 species of bats and found a convincing contrast in testes size. In species with monogamous
females, males had testes starting at 0.11 percent of their body weight and ranging up to 1.4 percent. But in
species where the females had a large number of mates, Pitnick found testes ranged from 0.6 percent to 8.5 percent
of the males' mass (in the Rafinesque's big-eared bat).
"If female
bats mate with more than one male, a sperm competition begins," Pitnick said. "The male who ejaculates the greatest
number of sperm wins the game, and hence many bats have evolved outrageously big
testes."
Promiscuity is known to make a difference in testicle size
in some other mammals. For example, chimpanzees are promiscuous and have testicles that are many times larger than
those of gorillas, in which a single dominant male has exclusive access to a harem of
females.
Large brains, meanwhile, are metabolically costly to develop
and maintain. Pitnick's research suggested that in those bat species with promiscuous females, the male's body
used more of its energy to enhance the testes — giving it the greater adaptive advantage — and lacked the energy it
needed to further develop the brain.
The study found that in more
monogamous species, the average male brain size was about 2.6 percent of body weight, while in promiscuous species,
the average size dipped to 1.9 percent.
___