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[Vol. 85 
classes comprising 30, 20, and 50% of the total colony, there is no 
age polyethism if those age classes perform 30, 20, and 50% 
respectively of any task. The data show that the age classes of both 
physical castes do not perform tasks in proportion to their numbers 
(Table 3). On the basis of X" comparisons, for most tasks with 
adequate sample sizes the null hypothesis can be rejected because 
there are significant differences between the observed and expected 
frequencies. This indicates that there is age-based division of labor 
in both physical castes (Table 4). Four tasks by minors (assist ecol- 
sion, allogroom majors, trophallaxis with minors, and carry exu- 
viae) are performed without apparent age bias, and eight behaviors 
by minors and one by majors were observed too rarely to permit 
assessment. 
Thus of behaviors with an adequate sample size, for P. hortensis 
minors 13 of 17, and for majors four or five, behaviors show age- 
based division of labor. 
4. Continuous versus discrete age castes. 
Wilson (1976a) states that division of labor is discretized if there is 
an exclusive association between (sets oO tasks and age class(es) and 
that it is continuous under all other conditions of age class/task 
association. The general question of age polyethism has two parts. 
Given that some tasks are performed more or less often by certain 
age classes, can adjacent age classes be combined because they show 
similar performance patterns? And second, are such associations 
between age class(es) and tasks exclusive? To test for associations, 
we calculated relative performance measures (RPM) for each age 
class by behavior. This descriptive way of treating the data controls 
for variation in age class size and in number of performances 
observed per age class, and it permits comparison between fre- 
quently and rarely occurring behaviors, as well as comparisons of 
age class performances within and between behaviors. 
Figure 1 shows that there are no consistent similarities between 
the relative performance probabilities for any pairs of adjacent age 
classes. This implies that no pair of age classes can be combined, 
and that these age classes do differ behaviorally, representing real 
castes. It is also clear that the associations between age castes and 
tasks or groups of tasks are not exclusive: the age-based division of 
labor is continuous rather than discretized in both the minor and 
