The annual ovarian cycle of Chrysemys picta: Correlated changes in plasma steroids and parameters of vitellogenesis

Seasonal variation in plasma and corpus luteum oestradiol-17β and progesterone concentrations of the lizardCordylus p. polyzonus(Sauria: Cordylidae)

“…During this time oviducLI, fat bodies and livers also show weight increases in Cordylus p. polyzonus (Flemming & Van Wyk 1992). Similar results reported for other reptiles (Lance & Callard 1978;Callard & Ho 1980;Licht 1984) suggest regulation of vitellogenesis by oestrogens in Cordylu.< p. polyzonus. Although progesterone is believed to be primarily associated with ovulatory and post-ovulatory evcnLI, it may play an important role in the preovulatory phase of vitellogenic activity (Licht 1984).…”

“…There was evidence of an increase in plasma progesterone concentrations during late vitellogenesis in female Cordylus p. polyzofllts, but concentrations during this Lime did not differ significantly from that of prcvitcllogenic and early vitellogcnic females. Significant incre<>scs in progesterone concentrations during vitellogenesis were reported for some reptiles (Callard, Lance, Salhanick & Barad 1978;Bona-Galla, Lich~ Veith 1974;Lance & Callard 1978). It has been illustrated that in many reptiles, progesterone docs not act synergistically with oestrogens and has an inhibitory effect on the growth of ovarian follicles and vitellogenesis (Callard & Doolittle 1973;Callard & Klotz 1973;Klicka & Mahmoud 1973;Veith 1974;Yaron & Widzer 1978;Licht 1982).…”

Environmental sex determination in a reptile varies seasonally and with yolk hormones

“…Similar variation between clutches has been found for other reptiles with TSD (Conley et al 1997;Janzen et al 1998). We expected hormone levels within a clutch to be strongly correlated among eggs (Conley et al 1997;Janzen et al 1998) because all ovarian follicles contributing to a clutch undergo vitellogenesis simultaneously (Callard et al 1978). Indeed, the correlation between clutch mates was positive and very high for E 2 (mean rˆ0.872 and pˆ0.0001) and positive but not signi¢cantly so for T (mean rˆ0.335 and pˆ0.129).…”

Temperature-Dependent Sex Determination in Vertebrates

“…A strong correlation between initial E 2 and T levels was also reported for painted and snapping turtles (Elf et al 2002a), indicating that female yolks with greater E 2 concentrations usually have greater T as well. In the painted turtle, Callard et al (1978) reported large increases in plasma E 2 and T during the preovulatory period, but the T levels were approximately four times greater than E 2 levels. They hypothesized that T was important as a precursor for E 2 in tissues expressing aromatase activity.…”

“…They found that implanted females had increases in systemic circulation of the respective hormones and subsequent increases in yolk hormone content in developing follicles compared with controls. Callard et al (1978) reported a direct relationship between circulating plasma E 2 levels and vitellogenin in the painted turtle (Chrysemys picta), with the largest E 2 peak occurring in the spring at the time of preovulation. They also document peaks in T and progesterone (P) just slightly later, during ovulation.…”