Ecotoxicology of Morelet's crocodile in Belize

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Title: Ecotoxicology of Morelet's crocodile in Belize
Author: Rainwater, Thomas Robert
Abstract: Over the last two decades , population declines and reproductive impairment have been observed in American alligators (Alligator mississppiensis ) inhabiting Lake Apopka , a highly contaminated lake in Florida , USA . Juvenile alligators from the lake have exhibited altered sex -steroid hormone concentrations , abnormal gonadal morphology , and reduced phallus size compared to alligators from a reference lake . No direct cause -effect relationship has been established between these reproductive and endocrine anomalies and environmental contaminants , but results of laboratory and field investigations suggest the potential for contaminant -induced endocrine disruption at various levels of organization in these animals . Although various environmental contaminants considered to be endocrine disrupters have been found in eggs and tissues of crocodilians worldwide , no studies have yet investigated endpoints of endocrine disruption in wild crocodilians outside of Florida . The primary objective of this study was to address this data gap by examining ecotoxicological endpoints in another crocodilian species living in habitats contaminated with endocrine -disrupting chemicals (EDCs ) , and where appropriate , compare results from this study with those observed for alligators in Florida . During a pilot study in 1995 , multiple organochlorine (OC ) pesticides considered to be EDCs were found in eggs of Morelet's crocodiles (Crocodylus moreletii ) from three localities in northern Belize . Based on these findings and previous data from Florida showing egg contamination , population declines , and reproductive abnormalities in alligators exposed to many of the same chemicals , a multi -year study was initiated to examine various endpoints of contaminant exposure and response in Morelet's crocodiles living on contaminated and reference sites in northern Belize . Gold Button Lagoon , a man -made lagoon from which contaminated crocodile eggs were collected in 1995 , was selected as the contaminated site for this study , while New River Watershed , a more remote site with fewer anthropogenic inputs than Gold Button Lagoon , was selected as the reference site . Three primary endpoints of endocrine disruption were evaluated in this study . First , vitellogenin induction was examined as an endpoint of exposure to exogenous estrogens or estrogen -mimicking contaminants . Vitellogenin is an egg -yolk precursor protein expressed in all oviparous and ovoviviparous vertebrates . Male and juvenile females normally have no detectable concentration of vitellogenin in their blood but can produce it following stimulation by an exogenous estrogen , such as an EDC . Thus , the presence of vitellogenin in the blood of male or juvenile female crocodiles can serve as an indicator of exposure to an estrogen -mimicking EDC . Of 358 males and juvenile females sampled in this study , no vitellogenin induction was observed , suggesting these animals were likely not exposed to estrogenic xenobiotics . However , many of the animals sampled were later found to contain OC pesticides in their caudal scutes , confirming they had in fact been exposed to OCs (and EDCs ) . These data suggest the lack of a vitellogenic response should not necessarily be interpreted as an indication that no exposure or other contaminant -induced biological response has occurred . Second , plasma sex -steroid hormone concentrations were examined as an endpoint of response to EDC exposure in crocodiles from the two study sites . The selection of this endpoint was based on numerous studies reporting altered concentrations of estradiol -17P (E2 ) and testosterone (T ) in alligators from Lake Apopka and other contaminated lakes in Florida . In the present study , few inter -site differences in plasma hormone concentrations were noted . No significant differences in plasma E2 concentrations were detected between sites . However , juvenile males and females from the contaminated site exhibited significantly reduced plasma T concentrations compared to juvenile males and females from the reference site , respectively . This finding was consistent with results from previous studies on alligators in Florida . No other inter -site differences in hormone concentrations were observed . Relationships between body size and hormone concentrations were variable and showed no clear pattern . Third , male phallus size was examined as a second endpoint of response to EDC exposure in crocodiles from the two study sites . Concurrent with reductions in plasma T concentrations , male alligators from Lake Apopka and other contaminated lakes in Florida have exhibited smaller phallus size compared to animals from a reference lake . Researchers speculate that abnormal hormone concentrations during early life stages may affect anatomical structures dependent on these hormones for proper growth and development (i .e . , genitalia ) . p ,p ' -DDE , a known anti -androgen , has been detected in alligator eggs and serum from Lake Apopka and was also detected in eggs and scutes of Morelet's crocodiles from the two Belize study sites . Thus , in the present study , male crocodile phallus size and plasma T concentrations were examined as endpoints of response to p ,p ' -DDE exposure as well as exposure to other contaminants . No differences in mean phallus size were observed between sites , whereas mean plasma T concentrations in juveniles from Gold Button Lagoon were significantly reduced compared with those from New River Watershed . It was discovered late in the study that New River Watershed exhibited a contaminant profile similar to that observed at Gold Button Lagoon , with multiple OCs detected at similar concentrations in sediments , crocodile eggs , and crocodile caudal scutes at both sites . With the lack of a suitable reference site , it is thus unclear if steroid hormone concentrations and male phallus size observed in this study are within the normal range exhibited by Morelet's crocodiles living in non -contaminated habitats or if they are altered in some way (e .g . , increased , reduced ) . In addition , it is also unclear if inter -site differences in plasma T are the result of exposure to EDCs , natural variation , one or more undetermined factors (e .g . , stress ) , or a combination of these factors . In general , the results of this study indicate few or no effects of EDC exposure on Morelet's crocodiles inhabiting contaminated wetlands in northern Belize . However , multiple uncertainties encountered in this study make inter -site and inter -study (crocodile to alligator ) comparisons difficult and some results equivocal . Thus , the potential effects of EDCs and other contaminants on crocodiles inhabiting these sites should not be assumed to be negligible . Long -term studies are essential to adequately assess the effects of EDCs on crocodilian populations , as these animals are long -lived and many contaminant -induced effects are organizational in nature , occurring during embryonic development but not appearing until later in life .
URI: http : / /hdl .handle .net /2346 /8649
Date: 2003-08

Citation

Rainwater, Thomas Robert Ecotoxicology of Morelet's crocodile in Belize. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /8649 .

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