Genetic Variation in AhR Gene Related to Dioxin Sensitivity in the Japanese Field Mouse, Apodemus speciosus

Human beings have developed many tools, technologies, and chemicals for their convenience and comfort. For example, herbicides and/or insecticides that are sprayed on crop lands prevent damage from pests and have resulted in remarkable increases in crop yield. Polychlorinated biphenyls (PCBs), which have insulating properties and are incombustible, were widely used in the past in electronic instruments and by the electric industry. However, some of these chemicals have harmful effects on organisms. In Seveso, Italy, a large amount of dioxins was emitted by explosion of an agrochemical factory. This accidental release of dioxins killed a lot of farm animals and many people living near the factory developed skin inflammation due to exposure to the high concentrations of dioxins. As seen above, many similar chemical spill disasters have occurred and new chemicals are still being produced. Dioxins are one of the most toxic groups of manmade chemicals known. Dioxins are not only highly toxic, but they also insidiously disrupt reproductive function by mimicking the actions of hormones in the body. Their effects on reproduction, such as reducing the number of sperm and affecting the sex ratio in offspring, may impair the fitness of individuals. Decreased reproductive success of individuals in a population may result in the extinction of local populations and eventually species extinction. In this chapter, we describe the effects of the most toxic chemical pollutant, dioxins, on the Japanese field mouse, Apodemus speciosus. We also discuss the diversity of dioxin sensitivity and attempted to identify dioxin sensitivity in mice using a molecular indicator. Our findings suggest that it is important to take into consideration the differences in dioxin response in each mouse for an accurate estimation of the impact of the pollution.