164 
Crews 
gradually declines as territorial boundaries 
become recognized and that the territorial 
males’ behavior shifts to courtship with the 
arrival (emergence) of females (Brown, 
1975). This shift from male-male aggression 
to male courtship, then, would act in concert 
with the environmental stimuli to facilitate 
OR. Thus, females would effectively offset 
their increased vulnerability to predators by 
rapidly attaining reproductive condition. 
Simultaneous male-female emergence, on the 
other hand, would expose females to the high 
frequency of male-male aggression necessary 
for the establishment of territories — which 
I have demonstrated experimentally inhibits 
ovarian development. Similarly, courtship 
facilitation and aggression inhibition of 
environmentally induced ovarian activity 
might also act to insure breeding synchrony 
in the population (e.g., the “Fraser Darling 
Effect”). For example, vitellogenesis in fe- 
males which emerge early would be inhibited 
until the males had established their terri- 
tories. 
I would like to suggest, then, that while 
emergence from hibernation may be cued 
by both environmental and endogenous fac- 
tors, the rate at which females respond to 
these environmental cues may have been in- 
fluenced, through selection, to coincide with 
the waning of male-male aggression follow- 
ing the establishment of breeding territories. 
Thus, although these laboratory experiments 
do not demonstrate conclusively an adaptive 
significance of the facilitation and inhibition 
of environmentally induced ovarian activity 
by specific male behavior patterns in nature, 
they do suggest a possible function of dif- 
ferential emergence in temperate zone verte- 
brates that has not been suggested before 
and one that is amenable to field experi- 
mentation. 
CONTROL OF FEMALE SEXUAL 
RECEPTIVITY IN THE LIZARD, 
Anolis carolinensis 
I have also sought to identify the various 
factors controlling female sexual receptivity 
during the breeding season in A. carolinensis. 
When a female A. carolinensis is introduced 
into a cage containing a sexually active male, 
the male immediately challenges the intruder 
(Crews, 19755). If the female does not flee 
and/or attempt to hide from the male, the 
male will stop performing challenge displays 
and begin to court the female (see Table 1 
for identifying characteristics of these dis- 
play patterns). A female that remains stand- 
ing for the advancing male will invariably 
arch her neck, enabling the male to take a 
neck grip. The male then straddles the fe- 
male and, after pushing his tail beneath hers 
to oppose their cloacal regions, everts a single 
hemipenis. Once intromission has been 
achieved, the male and female cannot be 
separated easily, possibly as a result of hemi- 
penile tumescence. There is no noticeable 
pelvic thrusting by the male during copula- 
tion. Separation occurs when the male dis- 
mounts and moves away from the female. 
Females often remain immobile following 
the male’s withdrawal, sometimes for as 
long as 10 minutes. 
Cycles of Sexual Receptivity (Estrous) 
While there have been many experimental 
investigations relating often quite subtle 
ovarian changes with changes in sexual re- 
ceptivity, the vast majority of these have 
been confined to birds and mammals (Ber- 
mant and Davidson, 1974). In one of the 
few such studies with reptiles, Noble and 
Greenberg (1941) suggested a similarity 
between A. carolinensis and mammals in 
that there existed a direct casual relation- 
ship between maturation of the ovarian 
follicle and sexual receptivity. The approach 
of Greenberg and Noble was to ovariectomize 
females and later implant crystalline hor- 
mones and note changes in genital morphol- 
ogy and sexual behavior. This only demon- 
strated that sexual receptivity was depend- 
ent upon the presence of the ovaries. I set 
out to test Noble and Greenberg’s hypothesis 
more directly by comparing the changes in 
