Reptiles

One of the most influential studies concerned with endocrine disruption in aquatic wildlife is that of Guillette and co-workers on the alligators of Florida. The genesis of this ongoing study was the finding that one particular population of alligators (Alligator mississippiensis), living on Lake Apopka, showed a dramatic decline during the 1980s that continues to the present day [34]; population density on this lake is now only about one-tenth of what it was in the 1970s. Lake Apopka is a pollution "hot spot", due to the fact that it was contaminated by a major pesticide spill in 1980 (see [35] for details of exactly what pollutants were released). The lake is also located in a heavily agricultural area, and hence probably receives significant pollution via run-off.

Guillette et al. [3] studied juvenile alligators from Lake Apopka, and compared them with animals of similar age from Lake Woodruff, a control (unpolluted) lake. They found that juvenile female alligators from Lake Apopka had plasma oestradiol concentrations 50% higher than those in females from the control lake. The Apopka females also exhibited abnormal ovarian morphology, with large numbers of polyovular follicles and polynuclear oocytes. Males were also affected; juvenile male alligators from Lake Apopka had much lower plasma testosterone concentrations compared to the concentrations found in the control males. Further, males from Lake Apopka had poorly organised testes and abnormally small penises [3,36]. It is thought that these effects were induced by pollutants at a very early stage of development of the alligators, probably in ovo; that is, they are so-called organisational effects. Subsequent research has shown that at least some of these effects persist for years [37], and that alligators in other lakes subjected to man's influence also appear to have been affected [37].

As will be discussed later, it has proved very difficult to determine exactly what caused these effects on the reproductive axis of alligators.

Very little evidence for (or against) endocrine disruption in other reptiles has been published. However, these are often large, and hence difficult, species to study, so perhaps this is not too surprising. A few papers (e.g. [38]) have reported preliminary data which have been interpreted to suggest that environmental contaminants might be adversely affecting some, but not all, reproductive indices in other species of reptiles, such as snapping turtles (Chelydra serpentina), but presently the available data are too sparse to reach any conclusions.

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