PhD ceremony: ms. B.V. Feldmeyer, 14.45 uur, Academiegebouw, Broerstraat 5, Groningen
Thesis: The effect of temperature on sex determination
Promotor(s): prof. I. Pen, prof. F.J. Weissing, prof. L.W. Beukeboom
Faculty: Mathematics and Natural Sciences
Barbara Feldmeyer studied the interaction of temperature and genes leading to sexual development. She used the housefly as experimental model and developed evolutionary models based on new insights. In most animals the genes dictate whether an individual develops into a male or a female. For example, in humans and other mammals maleness is determined by the Y chromosome. However, in many cold-blooded animals, such as reptiles and fish, the sex of an individual is determined by the temperature of its environment. Recent work on the molecular basis of sex determination challenges the classical dichotomy between genetic sex determination (GSD) and temperature dependent sex determination (TSD). Underlying gene networks are quite similar and small changes can convert a GSD system into TSD and vice versa. Moreover, several species have been discovered where both genes and temperature affect sexual development. Feldmeyer developed based her evolutionary models on these new insights. Her models show that mixtures of GSD and TSD can evolve easily and that rapid evolutionary transitions between GSD and TSD are expected, in agreement with observations. A detailed model based on field data from the snow skink, a live-bearing lizard where some populations have TSD and others GSD, correctly predicts the evolved sex determining system based on local temperature variation and demography of the lizards. In the housefly, different GSD systems coexist and are distributed along a north-south cline on the northern hemisphere. Feldmeyer discovered a very similar but opposite south-north cline on the southern hemisphere, and analysis of climatic conditions of the different housefly populations showed that temperature is an important but not the only climatic factor that can explain this.
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