| Since the early 1900s, the lakes of the Ocklawaha Basin in central Florida have experienced ecological degradation due to anthropogenic development. One species affected by degradation has been the American alligator ( Alligator mississippiensis). Decreased clutch viability (proportion of eggs in a nest that yield a live hatchling) was observed in the years after a chemical spill in which large amounts of sulfuric acid and dicofol, an organochlorine pesticide (OCP), flowed into Lake Apopka. Lake Apopka and other lakes in the Ocklawaha basin have also been contaminated by urban sewage and agricultural chemicals, with agricultural chemicals entering the lakes via rainfall run-off or back-pumping of water from agricultural lands). Decreased hatch rates are a problem at Lake Apopka, as well as at other OCP-contaminated sites in Florida. The purpose of my study was to determine the causes for decreased clutch viability, and to test the hypothesis that maternal exposure to OCPs is associated with embryonic mortality in alligators.; Field studies involved collecting and artificially incubating eggs from reference sites (Lake Lochloosa) and from OCP-contaminated sites (Lakes Apopka, Griffin, and Emeralda Marsh Restoration Area) to evaluate clutch viability as a function of egg and maternal OCP concentrations. Nutrient content of eggs and histopathology and morphometrics of embryos were also evaluated to identify potential factors associated with embryo mortality. In addition, a novel laboratory experiment exposed a captive population of adult alligators to an OCP mixture, and compared OCP burdens in eggs and clutch viability with a captive control group.; Results of field studies suggested that OCP concentrations (ng total OCP/g egg yolk, Mean +/- SE) in reference site clutches (n = 19; 102 +/- 16) were significantly (a = 0.05) lower than those of Apopka (n = 23; 7,582 +/- 2,008), Griffin (n = 42; 1,169 +/- 423), and Emeralda Marsh (n = 31; 15,480 +/- 2,265). Clutches from reference sites also had significantly higher clutch viability (70 +/- 4%) than those of Apopka (51 +/- 6%), Griffin (44 +/- 5%), and Emeralda Marsh (48 +/- 6%). Furthermore, decreased thiamine concentrations in eggs may play a role in decreased clutch viability in wild clutches. Results of the captive study suggested that treated females produced eggs containing higher OCP concentrations (n = 7; 13,300 +/- 2,666) than controls (n = 9; 50 +/- 4). Eggs of treated females also exhibited decreased viability (9 +/- 6%) as compared to controls (44 +/- 11%). These field and laboratory studies support the hypothesis that maternal exposure to OCPs is associated with decreased clutch viability in American alligators, and that thiamine deficiency may also be a contributing factor in reduced clutch viability. |
