Differential resource use, growth, and the ontogeny of social relationships in the green iguana

Growth rates, resource use, and ontogeny of behavior patterns were examined in captive groups of juvenile green iguanas (Iguana iguana). Four groups were housed in large arenas where supplemental heat and perch sites were limited, whereas two control groups were housed in similar arenas without limited resources. Growth, frequency and types of displays, behavioral interactions, and the use of resources were monitored. By 35-70 days of age, male hatchlings in arenas with limited resources could be classified into two groups: rapid growing dominant individuals and slow growing subordinate individuals. Growth and dominance were not correlated with size of individuals at hatching. Digestive efficiency of males was related to dominance and access to limited resources, but all lizards exhibited a similar digestive efficiency when maintained at a constant ambient temperature. Dominant males used the resources, especially supplemental heat sources, twice as often as subordinate males. The dominant/subordinate relationships and accompanying skew in body size were not evident in the control groups, or in females of any group. At 105 days, control groups were introduced to conditions with limited resources, resulting in increased aggressive interactions and divergence in growth rates. Onset of adult behavioral patterns was related to body size, and the species-specific signature display was observed in dominant males up to several months before subordinate males. These results indicate that male green iguanas establish a dominance hierarchy immediately posthatching when resources are limited, and as a consequence, both physiological and behavioral maturation are delayed in subordinate individuals.