Alligators and Endocrine Disrupting Contaminants: A Current Perspective

Abstract

SYNOPSIS. Many xenobiotic compounds introduced into the environment by human activity have been shownto adversely affect wildlife. Reproductive disorders in wildlife include altered fertility, reduced viability of offspring, impaired hormone secretion or activity and modified reproductive anatomy. It has been hypothesized that many of these alterations in reproductive function are due to the endocrine disruptive effects of various environmental contaminants. The endocrine system exhibits an organizational effect on the developing embryo. Thus, a disruption of the normal hormonal signals can permanently modify the organization and future function of the reproductive system. We have examined the reproductive and developmental endocrinology of several populations of American alligator (Alligator mississippiensis) living in contaminated and reference lakes and used this species as a sentinel species in field studies. We have observed that neonatal and juvenile alligators living in pesticide-contaminated lakes have altered plasma hormone concentrations, reproductive tract anatomy and hepatic functioning. Experimental studies exposing developing embryos to various persistent and nonpersistent pesticides, have produced alterations in gonadal steroidogenesis, secondary sex characteristics and gonadal anatomy. These experimental studies have begun to provide the causal relationships between embryonic pesticide exposure and reproductive abnormalities that have been lacking in pure field studies of wild populations. An understanding of the developmental consequences of endocrine disruption in wildlife can lead to new indicators of exposure and a better understanding of the most sensitive life stages and the consequences of exposure during these periods.

Morphological abnormalities in gonads of the Baltic herring (Clupea harengus membras): Description of types and prevalence in the northern Baltic Sea

“…However, they may also remain unnoticed, if for instance the sexual maturity is determined without taking the entire gonad out so that its morphology can be seen properly. Beside the lake whitefish (Bernet et al 2004(Bernet et al , 2008, gonad anomalies have been found also in some tropical fish (Omotosho 1987), and especially frogs and reptiles suffer from this condition (e.g., Guillette et al 2000;Hecker et al 2006). In many cases, the anomalies are causally linked with the chronic exposure to herbicides (Coady et al 2005) or other environmental contaminants disturbing the endocrine system of an animal.…”

Hormonally mediated maternal effects, individual strategy and global change

“…For example, red-eared slider turtles exposed experimentally to pesticides or their metabolites display altered sex ratios at hatching, and the males are demasculinized as demonstrated by an increased oestrogen/androgen ratio of testicular hormone synthesis [100]. American alligators (Alligator mississippiensis) naturally or experimentally exposed to various oestrogens or pesticides (or their metabolites) exhibit altered gonadal steroidogenesis and abnormally developed phalli [101][102][103].…”

Evolutionary Perspectives on Sex Steroids in the Vertebrates

“…In cases of endocrine disruption, exposure levels are typically too low to have toxic or acute effects on adults (Colborn et al 1993), but affect organisms during critical organizational periods of early life stages (Guillette et al 1995). Tissue contaminant levels previously considered safe are sufficient to alter endogenous chemical mediation in fish Jobling et al 2006), amphibians (Hayes et al 2002;Hayes et al 2006;Hayes et al 2010), reptiles (Crews et al 1995;Guillette et al 2000), birds (Ottinger et al 2009), and mammals (Colborn et al 1993). …”