Journal of Theoretical Biology 2 s

d fo ine tion ast e o an beneficial effects. If sex determination is predominantly genetic but environmentally reversible, as is the case in many amphibia, reptiles, and fish, Trojan sex chromosomes could be introduced into populations in order to change sex ratios towards more females. We analyse the possible consequences for the introduction of XX-males (XX individuals that have been changed to phenotypic males in a XY/XX Courchamp et al., 1999; Stephens and Sutherland, 1999). population that loses genetic variability at the same rate as the real population (Falconer and Mackay, 1996). With family sex ratios and producing a higher ratio of the et al., 2006). The aim is to lower the sex ratio, defined here as the proportion of males, and hence to increase the production of females if they are the limiting factor for ARTICLE IN PRESSpopulation growth. Male-biased sex ratios have recently been modelled as a strategy for controlling the population sizes of non-nativ