Environmental sex determination in a reptile varies seasonally and with yolk hormones.
نویسندگان
چکیده
Most hypotheses that have been put forward in order to explain the persistence of environmental sex determination (ESD) in reptiles assume a relatively fixed association of sex with temperature-induced phenotype and no maternal influence on offspring sex. Here we demonstrate the association of maternally derived yolk hormone levels with the offspring sex ratio and describe two new aspects of temperature-dependent sex determination (TSD), i.e. seasonal variation in both thermal response and yolk steroid levels. Eggs from painted turtles (Chrysemys picta) were incubated at 28 degrees C. The hatchling sex ratio at 28 degrees C (i.e. the phenotypic reaction norm for sex at 28 degrees C) shifted seasonally from ca. 72% male to ca. 76% female. Yolk oestradiol (E2) increased seasonally while testosterone (T) decreased. The proportion of males in a clutch decreased as E2 levels increased and the E2:T ratio increased. These new findings are discussed in relation to heritability and adaptive explanations for the persistence of ESD in reptiles. Maternally derived yolk hormones may provide a mechanism for the seasonal shift in the sex ratio which in turn may help explain the persistence of ESD in reptiles. They may also explain those clutches of other reptiles with TSD that fail to yield only males at maximally masculinizing conditions.
منابع مشابه
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متن کاملTemperature-Dependent Sex Determination in Reptiles
The sex of a reptile [6] embryo partly results from the production of sex hormones [7] during development, and one such process to produce those hormones [8] depends on temperature of the embryo's environment. The production of sex hormones [7] can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination [9], also ca...
متن کاملTemperature-Dependent Sex Determination in Reptiles
The sex of a reptile [6] embryo partly results from the production of sex hormones [7] during development, and one such process to produce those hormones [8] depends on temperature of the embryo's environment. The production of sex hormones [7] can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination [9], also ca...
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ورودعنوان ژورنال:
- Proceedings. Biological sciences
دوره 267 1454 شماره
صفحات -
تاریخ انتشار 2000