Assessment of organochlorine pesticide residues in scutes from Morelet's crocodiles (Crocodylus morletii) inhabiting Belize

It has been documented that exposure to organochlorine compounds (OC) can cause significant alterations in biological processes In animals including disruptions in endocrine and reproductive processes. Biomarkers used by toxicologists to assess pesticide residues in animals are generally limited to exposure. However, DNA can provide a way to look at exposure and actual effects on species. Determining the genetic structure of populations of endangered species Is a way to not only detect environmental effects but also to guide conservation of the species. Variation in genotypes can be attributed to a number of factors including reproductive behavior and population dynamics.

The purpose of this study was to determine whether OC residues were present in crocodile scute tissue and whether a relationship existed between loci variance and the OC residue concentrations found in the scutes. This study undertook a comparative analysis of OC concentrations in Morelet's crocodile scutes and variations in nine microsatellite loci of crocodiles within and among certain populations. Located primarily in Central American freshwater and brackish water areas, Morelet's crocodile provides a perfect sentinel, as it is a top predator in the food chain and a native aquatic animal. Crocodiles are considered to be a keystone species In their ecosystem. There was a need for statistical population monitoring among crocodiles in Belize. Previous work was completed on the genetic structure among wild populations of Morelet's crocodiles in Belize. Highly variable polymorphic markers called microsatellite loci were used to determine variation within and among populations. Samples were collected from Morelet's crocodiles located near Lamanai Research Center, Indian Church Village, Orange Walk District, Belize. The samples were collected primarily around the New River and New River Lagoon area from May through September during 1998 and 1999. Dorsal dermal scutes were clipped from the crocodiles as a means of marking the crocodiles and for later use as a tissue sample. These scutes were analyzed to determine OC levels in tissue. A blood sample was also extracted from the dorsal sinus of the crocodile in order to determine the genetic structure of the nine microsatellite loci for each individual crocodile.