266 
Carpenter 
ask, what is the relationship between the 
display-action-pattern (a time-motion phe- 
nomenon) and the central nervous system 
control, or how is this behavior programed 
in the brain? Experimental neurologists are 
beginning to delve into this problem. With 
respect to physiological measures, we have 
used a polygraph to record changes in heart 
rate of displaying lizards (Sassaman, 1974) 
and have shown that temperature does not 
have a strong effect on the display perform- 
ance (McCardell, 1971). 
The significance of differences or similiari- 
ties in display-action-patterns of closely re- 
lated forms to allopatry and sympatry and 
their function as an isolating mechanism 
need further study. 
With the evidence indicating that the dis- 
plays are genetically determined, is it pos- 
sible to produce hybrid or intergrade individ- 
uals with intermediate displays? This will 
take perseverance and time because raising 
newly hatched or newly born lizards to 
maturity is a difficult task. 
A fascinating possibility for understand- 
ing the relationship between the social be- 
havior patterns of a species and its ecological 
niche requirements lies in the study of 
ecological homologs and equivalents. When I 
examined the book by Donoso-Barros (1966) 
on the reptiles of Chile, I was impressed by 
the frequent similarities in appearance be- 
tween certain species of the South American 
iguanid genus Liolaemiis and some of our 
North American iguanid species in the 
genus Sceloporus. 
Do these similarities relate to particular 
ecological adaptations, and, if so, are the 
social structures and the agressive displays 
also similar? Likewise, there are species of 
agamids in Australia that appear to be 
ecological equivalents of certain North 
American iguanids, the most striking being 
the ant-eating Moloch and Phrynosoma. How 
similar are their social behaviors, including 
their displays? Perhaps the agamid Physig- 
nathus has social behaviors quite similar to 
those of the iguanid genus Iguana. 
The question is : How did these ritualistic, 
species-specific display-action- patterns origi- 
nate with the early progenitors of the 
iguanids and agamids? 
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