Article Review: Seasonal variations in plasma vitellogenin and sex steroids in male and female Eastern Box Turtles, Terrapene carolina carolina

This is an article by Currylow, A. F., Tift, M.S Meyer, J.L Crocker, D.E., and Williams, R.N., that was written in General and Comparative Endocrinology. The researchers looked at reproductive physiology in the Eastern Box Turtle specifically, they looked at testosterone, estrogen, and vitellogenin levels. Vitellogenin is an egg yolk protein that is often used to assess if a female is reproductively active. Testosterone is a male sex hormone and estrogen is a female sex hormone. Recently, Eastern Box Turtle populations have been threatened due to habitat loss and human disturbances. According to the researchers, the reproductive physiology of free-ranging turtles has never been recorded, which can be very important in the recovery of this species.

The researchers selected a population of Eastern Box Turtles that were in central Indiana because this population was relatively undisturbed and also able reproduce successfully.  For methods, the researchers drew blood samples from the turtles and then would isolate and analyze the hormone and protein levels in the samples. They took samples from 111 turtles, 43 of the turtles were measured continuously every 2 months over a two-year period, while 68 turtles were encountered randomly.

The researchers found that across the year, males had two twin peaks of testosterone levels and the females had a single peak of estrogen and vitellogenin, usually these peaks occurred in the summer months when the turtles were most active. Males had two peaks of testosterone, one level when they go through spermatogenesis and when they are courting. Females had a peak in estrogen and vitellogenin when they were sexually active. Males tended to have higher overall testosterone levels if they had a smaller territory because they were more likely to encounter encroaching males or potential females. Some females that the researchers encountered had no presence of vitellogenin or estrogen, indicating that they were not sexually active at the time.

This data is useful because it establishes a base line of reproductive physiology for free-ranging Eastern Box Turtles. This data can now be used to compare to other populations that have suffered a greater amount of disturbance. Another useful part of this data was realizing that not all females were sexually active, indicated by lack of estrogen and vitellogenin. This means that it is likely that female Eastern Box Turtles, might not lay a clutch of eggs every year and thus the population at a whole will have a harder time recovering from disturbances. 

Article Link:http://dx.doi.org/10.1016/j.ygcen.2012.11.005 

Photo Reference: http://www.infoturtle.com/eastern-box-turtle/