It is not known whether the temperature sensitivity resides in the aromatase gene or protein itself or in other proteins that regulate it. Sex determination and differentiation. Location-dependent sex determination in Bonellia and Crepidula As mentioned in Chapter 3, the sex of the echiuroid worm Bonellia depends on where a larva settles.
Physiological and Biochemical Zoology.
Hatchlings from single-sex producing temperatures also had higher first-year survivorship than the hatchlings from the temperature that produces both sexes. Synergism between temperature and hormones has also been identified in these systems. The eggs are affected by the temperature at which they are incubated during the middle one-third of embryonic development.
For instance, polychlorinated biphenyls PCBs are pollutants whose molecules are structurally similar to some estrogens. However, there is no evidence thus far that sex ratio is manipulated by parental care. Spencer and Janzen found that hatchlings from mixed-sex nests were less energy efficient and grew less than their same-sex counterparts incubated in single-sex producing temperatures.
Charnier, Madeline. In this case—which governs all snake species—males are the homogametic sex ZZ and females are the heterogametic sex ZW. Developmental Dynamics. Although few previous studies had supported the theory in reptiles, Pieau proposed TSD as an alternative to genotypic sex determination.
Variations on this theme also exist. Temperature-dependent aromatase activity is also seen in diamondback terrapins, and its inhibition masculinizes their gonads Jeyasuria et al. The distinction between chromosomal sex-determination systems and TSD is often blurred because the sex of some species — such as the three-lined skink Bassiana duperreyi and the central bearded dragon Pogona vitticeps — is determined by sex chromosomes, but this is over-ridden by temperatures that are tolerable but extreme.