Dissertation Research: Theoretical and Experimental Investigations of Fisher's Sex Ratio Theory

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R.A. Fisher first proposed that there is a mechanism of selection for the evolution of a sex ratio of 1/2 males and 1/2 females in populations in which there is equal investment in males of females. Although the principles suggested by Fisher are widely accepted, no one has provided test results supporting them. Experimental testing of this theory is important to basic scientific research, but it requires an animal system with genetic variation in sex ratio. Variation of this type is found in the platyfish, Xiphophorus maculatus, a tropical freshwater fish which has three sex chromosomes (W,X,Y). This experiment will investigate sex ratio changes from one generation to the next in populations of platyfish which are initiated with sex ratios other than 1/2. The results will be compared to those predicted by computer simulations. This project will provide quantifiable results supporting a generally accepted theory of sex ratio evolution. This research is important not only to basic science, but also has potential applications to aquaculture. A thorough understanding of sex ratio evolution is necessary if sex ratio manipulation techniques are to be applied as a means to increase production. Manipulation of population sex ratios could greatly increase production by increasing the number of offspring produced in the following generation.