The influence of the environment on the endocrine and immune systems has become an extreme example of the extent of human influence and human potential to disrupt biological systems. Many natural aspects of the environment (i.e., temperature, food availability, and predator interactions) modify both the endocrine and immune systems. Exposure to xenobiotic chemicals can also modify endocrine and immune parameters, especially when exposure occurs during embryonic development. Furthermore, the endocrine system is an important regulator of the immune system. Therefore, the interactions between exposure to xenobiotics in wild populations of alligators and the following variables were considered: sex hormones and seasonal variation in sex hormones, stress response, morphology of the spleen and thymus, mitogenic response, and phagocytic response.

Seasonal variation in sex steroids was found in juvenile alligators. Plasma testosterone concentrations differed in contaminant-associated alligators relative to alligators from reference lake and the difference was influenced by the season. Contaminant-associated alligators also had a modified plasma corticosterone profile during capture stress; and, this modified response appears to be from an activational influence rather than a developmental effect. Several differences were also noted in immune parameters associated with the contaminated alligator population: an increase in the cortical region of the thymus, a reduction in lymphocyte presence in the spleen, and a greater proliferation response of lymphocytes. Alligators from the reference lake had sexually dimorphic characteristics in the spleen; no such difference was present in contaminant-associated alligators. Additionally, a morphological effect on the spleen and thymus was found in eggs treated with trans-nonachlor, a contaminant present in higher concentrations at the contaminated study site.

In conclusion, all organisms, including the American alligator live in a dynamic environment. Changing biotic and abiotic factors—including anthropogenic changes such as the presence of contaminants—must be transduced by the endocrine and immune systems of an organism to enable homeostatic mechanisms. This research provides evidence of additional possible effects of contaminant exposure to the immune system and the endocrine-immune systems of wild, juvenile alligators. The data are particularly important because they suggest seasonality in reproductive steroidogenesis of wild, juvenile alligators.