Using plasma vitellogenin in loggerhead sea turtles to assess reproductive maturation and estrogen-like contaminant exposure.

Vitellogenin (VTG), an egg yolk precursor, is abnormally produced by male and juvenile oviparous species upon exposure to estrogens. Plasma VTG in loggerhead sea turtles (Caretta caretta) helped us understand their reproductive maturation and investigate it as a biomarker of contaminant exposure. VTG presence was screened in plasma from 404 loggerheads from the Northwestern Atlantic Ocean using a freshwater turtle antibody in Western blots. VTG concentrations were semi-quantified using band intensities calibrated to results from a loggerhead-antibody ELISA. VTG detection and concentrations were highest to lowest: nesting females, in-water adult females, subadult females, smaller females, unknown sex, and males. Loggerheads from this region begin vitellogenesis ≅77 cm SCL. We classified VTG expression as abnormal in nine male or juvenile turtles. Organochlorine contaminant (OC) concentrations were measured in blood and/or fat biopsies of some turtles. One abnormal VTG female had the second highest fat polychlorinated biphenyl (PCB) and 4,4'-dichlorodiphenyldichloroethylene concentrations among 43 VTG-negative juveniles. The nine VTG-abnormal turtles had blood PCB concentrations 8.5 % higher, but not significantly different, than 46 VTG-negative juveniles (p=0.453). In turtles <77 cm, blood PCB concentrations were significantly, but weakly, correlated with semi-quantified VTG concentrations (tau=0.1, p=0.004). Greater blood OC concentrations were found in adult females than males, which motivated the creation of a conceptual model of OC, VTG and hormone concentrations across a reproductive cycle. A decision tree is also provided incorporating VTG as a sexing tool. Abnormal VTG expression cannot conclusively be linked to endocrine disruption caused by these OC concentrations. Studies should further investigate causes of abnormal VTG expression in wild sea turtles. This article is protected by copyright. All rights reserved. Environ Toxicol Chem 2023;00:0-0. © 2023 SETAC.