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Re: Size Does Matter in Bats' Evolution

I _knew_ there had to be a reason I am not as smart as y'all are... it is so 
obvious now that Dr. Kates has mentioned it.
Brain small, and getting smaller... 


----- Original Message ----
From: Allan Edels <edels@msn.com>
To: dinosaur@usc.edu
Sent: Tuesday, January 24, 2006 9:55:31 AM
Subject: Size Does Matter in Bats' Evolution

This might be of interest:

Size Does Matter in Bats' Evolution By WILLIAM KATES, Associated Press 
15 minutes ago  [i.e. 9:45 AM EST - 1/24/2006]

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 

"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 

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.


Allan Edels