Plasma Vitellogenin and Testosterone in Diamond-backed Terrapins (Malaclemys terrapin) during the Nesting Season in Coastal New Jersey
>Vitellogenesis is the process in which female oviparous vertebrates synthesize the protein vitellogenin to develop egg yolk. In some species, vitellogenin has been used to investigate reproductive status, as a biomarker of clutch size and nesting frequency, and as a biomarker of exposure to endocrine-disruptive chemicals. The Diamond-backed Terrapin (>Malaclemys terrapin>) is an obligate coastal species that in the northern extent of its range nests in the spring and summer months. Diamond-backed Terrapins serve as a key indicator species of coastal ecosystem health; thus, furthering our understanding of the endocrine control of reproduction may inform biologists of the health and status of coastal ecosystems. The objective of this study was to quantify baseline values of vitellogenin and testosterone in Diamond-backed Terrapins during the nesting season, in the northern part of their range. Blood samples were taken from adult female terrapins from two populations in coastal New Jersey from June–August. Enzyme-linked immunosorbent assays (ELISAs) were used to quantify vitellogenin (VTG) and testosterone (T) across the nesting season. VTG concentrations showed peak values in the earliest part of the nesting season, significantly declining through the summer before reaching basal values in August, with T showing a similar trend. This suggests that terrapins in New Jersey follow a similar reproductive cycle to other turtle species from temperate latitudes. Additionally, we found that larger females exhibited higher concentration of T and VTG than smaller females. This suggests that VTG and T are useful biomarkers of reproductive output in these animals. Lastly, we also noted that larger females tended to nest earlier in the nesting season than smaller females. We hypothesize that larger females may compete for resources more effectively and efficiently than smaller females, which may confer larger individuals a fitness advantage.
Mean plastron length (± SEM) of Diamond-backed Terrapins captured during early (June), middle (early July), and late (late July–early August) nesting season. Dashed lines within each box indicate mean of data, while solid lines inside the boxes indicate the median. Varying letters indicate significant differences (P < 0.05) between sampling periods. Mean and median overlap in some categories, and both lines may not be visible.
Mean circulating plasma (A) testosterone concentration (± SEM) and (B) vitellogenin concentration (± SEM) of Diamond-backed Terrapins captured during early (June), middle (early July), and late (late July–early August) nesting season. Dashed lines within each box indicate mean of data, while solid lines inside the boxes indicate the median. Varying letters indicate significant differences (P < 0.05) between sampling periods. Mean and median overlap in some categories, and both lines may not be visible.
Plasma testosterone (A) and vitellogenin (B) concentrations in relation to midline plastron length in Diamond-backed Terrapins captured during early (June; green triangles), middle (early July; blue squares), and late (late July–early August; red circles) nesting season at the Cape May Peninsula, New Jersey and the Hackensack Meadowlands, New Jersey.
Contributor Notes
Associate Editor: J. Kerby.