238 
Ferguson & Bohlen 
predictability to result in the evolution of any 
adaptive mechanisms in the adult, egg-pro- 
ducing females? W. Kenneth Derickson, as 
part of his comparison of lipid cycling in 
two species of Sceloporus (1976) demon- 
strated that females of a given body length 
(55 mm) contain roughly the same amount 
of energy in an early and a late clutch of 
eggs (Table 8). However, females sampled 
late in the egg-laying season produced sig- 
nificantly fewer but larger eggs than females 
sampled early in the egg-laying season. The 
larger eggs resulted in significantly larger 
hatchlings. Thus, there seems to be an adap- 
tive shift in energy allocation as the egg- 
laying season progresses. Early in the sea- 
son, females divided their energy into more 
but smaller packages which produce more 
but smaller offspring early in the hatching 
season when hatchling size does not corre- 
late with fitness significantly. Later in the 
season, females divide their energy into 
fewer but larger packages which produce 
larger offspring later in the hatching season 
when larger hatching size does correlate 
with a fitness advantage. 
Aggressiveness 
If dominance is responsible for a higher 
fitness, all predictors of dominance, such as 
size, should be correlated with fitness. Ag- 
gressiveness is also a predictor of dominance 
(Guhl, 1956). Although the quantitative as- 
sessment of degree of aggressiveness has 
proven elusive, ethologists generally agree 
that the tendency to behave aggressively 
toward a conspecific varies. Eisenberg 
(1967) and Philibosian (1975) have em- 
ployed crowding intolerance as a compara- 
tive measure of aggressiveness of different 
species of rodents and Anolis lizards, respec- 
tively. In spiny lizards the difference in sur- 
vivorship between crowded and isolated 
hatchling lizards was not significant at the 
.05 level in the experiment using early hatch- 
lings; but the grouped lizards survived sig- 
nificantly less in the experiment using later 
hatchlings (Table 9). Also, the survival of 
Table 8. Reproductive energetics of adult 
female and juvenile spiny lizards. Data 
are adapted from those of Derickson 
(1976). The first three parameters were 
taken from regression line equations of the 
parameters versus snout-vent length and 
are for females 55 mm in length. Signifi- 
ficance value designations same as in previ- 
ous tables and are those given by Derick- 
son for the probability of differences due 
to chance of the regression lines. 
Early Clutches Late Clutches 
Calories/ 
clutch 4335 4707 
Clutch size 6.5 eggs * 5.5 eggs 
Calories/egg 667 ** 854 
Mean 
hatchling 
size (mm) 22.8 ** 24.1 
grouped early hatchlings was significantly 
greater than that of grouped late hatchlings. 
In summary, a decreasingly plentiful food 
supply for later emerging hatchlings has re- 
sulted in the evolution of a variable energy 
allocation mechanism in females. This mech- 
anism results in fewer but larger, more ag- 
gressive hatchlings late in the season when 
the competitive environment of juveniles is 
more severe. 
VISIBILITY, PREDATOR DETECTION, 
CONSPECIFIC COMMUNICATION, 
AND GEOGRAPHIC VARIATION 
OF SIGNATURE DISPLAYS 
Introduction 
The signature display (Stamps and Bar- 
low, 1973) was originally described by Car- 
penter and Grubitz (1961). It is a stereo- 
typed species- or population-typical display 
performed by iguanid and agamid lizards of 
many species. The most common features of 
the display include pushup, nodding, and 
or dewlap extension movements. While seen 
