Plasma Vitellogenin in Free-Ranging Loggerhead Sea Turtles (Caretta caretta) of the Northwest Atlantic Ocean

Abstract

Vitellogenin is the egg yolk precursor protein produced by oviparous vertebrates. As endogenous estrogen increases during early reproductive activity, hepatic production of vitellogenin is induced and is assumed to be complete in female sea turtles before the first nesting event. Until the present study, innate production of vitellogenin has not been described in free-ranging sea turtles. Our study describes circulating concentrations of vitellogenin in loggerhead sea turtles (Caretta caretta) from the Northwest Atlantic Ocean. We collected blood samples from juveniles and adults via in-water captures off the coast of the Southeast USA from May to August, and from nesting females in June and July at Hutchinson Island, Florida. All samples were analyzed using an in-house ELISA developed specifically to measureCaretta carettavitellogenin concentration. As expected, plasma vitellogenin declined in nesting turtles as the nesting season progressed, although it still remained relatively elevated at the end of the season. In addition, mean vitellogenin concentration in nesting turtles was 1,000 times greater than that measured in samples from in-water captures. Our results suggest that vitellogenesis may continue throughout the nesting season, albeit at a decreasing rate. Further, vitellogenin detected in turtles captured in-water may have resulted from exposure to endocrine disrupting chemicals.

The physiology of lipid storage and use in reptiles

“…In reptiles, genes for vitellogenin have been reported for Anolis carolinensis (Alföldi et al., ). Additionally, vitellogenin proteins have been identified in several reptiles (Ho, L'Italien & Callard, ; Ho et al., ; Gavaud, ; Selcer & Pamer, ; Heck et al., ; Duggan et al., ; Morales, Pagán & Gómez, ; Romano et al., ; Smelker et al., ). Vitellogenin increases in plasma concentration during seasonal ovarian growth (Rostal et al., ; Duggan et al., ; Rosanova et al., ) and is produced in response to oestrogen stimulation (Hahn, ; Ho et al., ; Gavaud, ; Cree et al., ; Selcer & Pamer, ; Heck et al., ; Rosanova et al., ; Duggan & Callard, ; Herbst et al., ).…”

“…Although these egg‐laying events may be separated by several weeks, this inter‐nesting period is not used for vitellogenesis of later clutches; rather, vitellogenesis is complete for all clutches by the time females arrive from their migration at the nesting ground (Rostal et al., ; Limpus et al., ; Rostal, ). Nonetheless, levels of plasma vitellogenin and triglycerides continue to be elevated, but decline with successive nesting events (Hamann et al., ; Goldberg et al., ; Smelker et al., ).…”

“…If vitellogenesis is complete, why are these yolk precursors still circulating? Levels of vitellogenin and triglycerides may rise as a side‐effect of elevated oestrogen levels (Smelker et al., ). Oestrogen is involved not only in coordinating vitellogenesis, but also other events of reproduction including nesting (Owens, ; Kakizoe et al., ).…”

The current state and future directions of marine turtle toxicology research

“…Only one of the six publications that investigated vitellogenin (Vtg) as a biomarker of disruption to the reproductive process correlated Vtg levels with organic contaminant concentration (Keller, 2003). Two used exogenous E 2 injections to induce Vtg production (Herbst et al, 2003;Sifuentes-Romero et al, 2006), while three only examined the presence of vitellogenin in marine turtles (Valverde et al, 2008;Zaccaroni et al, 2010;Smelker et al, 2014). One publication investigated the application of the comet assay for assessing DNA damage in C. caretta for future use in toxicological studies (Caliani et al, 2014), and one publication correlated levels of metals with metallothionein production in two species of turtle (C. mydas and C. caretta) (Andreani et al, 2008).…”

“…Detection in wild populations is an important step in the process of identifying a biomarker, as baseline levels of a protein or enzyme in unexposed individuals must be quantified to validate biomarker use (Smelker et al, 2014). The most commonly investigated protein in marine turtles is vitellogenin (Vtg), which has been the focus of six publications.…”