Thesis

Ecotoxicology of free-ranging western pond turtles (emys marmorata)

This study investigated the potential effects of cholinesterase (ChE) inhibiting pesticides and thyroid hormone changes from blood mercury (Hg) concentrations in western pond turtles (Emys marmorata) occupying streams in two regions of California, USA. The southern region is suspected of having increased exposure to atmospheric deposition of pesticides originating from Central Valley agriculture compared to the northern region. Total ChE activity of turtles was significantly depressed by 31% (p = 0.005) in the southern region after accounting for additional sources of variation in ChE activity. Male turtles had significantly increased ChE activity compared to females (p = 0.054), but cloaca temperature, length, mass, handling time, body condition, and lymph presence were not significant predictors of turtle ChE activity. Conversely, turtles in the northern region were suspected of having increased Hg exposure from historic gold mines compared to the southern region. Erythrocyte Total Hg (THg) concentrations in turtles ranged from 0.179 to 3.197 mg kg-1, with the highest mean concentrations found in the northern region and the lowest in the southern region. A positive correlation between mean turtle erythrocyte THg concentrations and the number of historic gold mines within a study watershed may exist (p = 0.057). Plasma triiodothyronine and thyroxine (T4) concentrations were not significantly influenced by THg concentrations, although T4 was significantly related to capture time of day (p = 0.042) and body mass (p = 0.031), and males had increased plasma T4 compared to females (p = 0.001).

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