Variation in sex determination and the application of the YY male technology for the production of all-male populations of the tilapia Oreochromis mossambicus

[摘要] ENGLISH ABSTRACT: Tilapia is presumed to have a well-defined genetic mechanism of sex determination, but notall sex ratios are compatible with a monofactorial sex determination model. A theory ofautosomal gene influence, as well as temperature sex determination (TSD) has been proposedin order to explain large variations in sex ratios. This study assessed the variation in progenysex ratio in O. mossambicus as a basis for the application of YY male technology in theproduction of all-male progeny groups.Three populations of O. mossambicus were sampled that are representative of thegeographical distribution of the species in Southern Africa. Progeny groups were producedfrom randomly selected parents and maintained at constant temperature during the labileperiod of sex differentiation. Variation in sex ratios between different families of the samestrain as well as between different strains was calculated. No significant differences wereobserved in sex ratio between strains, though a significant intra-group variation wasidentified. This study identified both male and female-biased sex ratios. The data in generalconform to a monofactorial sex determination model. Male-biased sex ratio observed in onestrain can possibly be ascribed to temperature sex determination (TSD). This strain ofO. mossambicus originated from an area with different annual temperature patterns and thepossibility of TSD having an adaptive advantage is discussed.This thesis also presents the results of a program to produce monosex male tilapiathrough the application of the YY male technology in O. mossambicus. Viable XY femaleand YY male genotypes were produced. XY females sired progenies ranging from 68-94%male ofspring, while YY males sired a mean progeny of 94% male phenotypes. From theseresults it is concluded that YY male technology provide a viable method for the production ofall-male progeny in O. mossambicus. Once available on a commercial scale, the technologycan be made more reliable through the application of the appropriate selection methods.

[发布机构] Stellenbosch University