Possible ecological risks of transgenic organism release when transgenes affect mating success: Sexual selection and the Trojan gene hypothesis

Widespread interest in producing transgenic organisms is balanced by concer n over ecological hazards, such as species extinction if such organisms wer e to be released into nature. An ecological risk associated with the introd uction of a transgenic organism is that the transgene. though rare, can spr ead in a natural population. An increase in transgene frequency is often as sumed to be unlikely because transgenic organisms typically have some viabi lity disadvantage. Reduced viability is assumed to be common because transg enic individuals are best viewed as macromutants that lack any history of s election that could reduce negative fitness effects. However, these argumen ts ignore the potential advantageous effects of transgenes on some aspect o f fitness such as mating success. Here, we examine the risk to a natural po pulation after release of a few transgenic individuals when the transgene t rait simultaneously increases transgenic male mating success and lowers the viability of transgenic offspring. We obtained relevant life history data by using the small cyprinodont fish, Japanese medaka (Oryzias latipes) as a model. Our deterministic equations predict that a transgene introduced int o a natural population by a small number of transgenic fish will spread as a result of enhanced mating advantage, but the reduced viability of offspri ng will cause eventual local extinction of both populations. Such risks sho uld be evaluated with each new transgenic animal before release.