immunoreactivity. Habitat and distribution The eastern fence lizard is found in Alabama, Louisiana, Arkansas, Colorado, Georgia, North Carolina, South Carolina, West Virginia, Virginia, Indiana, Kentucky, Southern Illinois, Southern Indiana, Tennessee, Ohio, Pennsylvania, Maryland, Missouri, Mississippi, Delaware, northern Florida, southern Wyoming, northeastern Pennsylvania, southern New Jersey, and southeastern New York. It prefers open woodland and the edges of forests. There are some introduced populations of eastern fence lizards, the most well known in Staten Island, New York. In 1942, Carl Kauffeld released 29 of the lizards near Rossville where they still persist today in post oak-blackjack oak barrens. This introduction was done so Kauffeld could have an easy source of food for the lizard-eating snakes at the Staten Island Zoo, as he would otherwise have to drive to the Pine Barrens to collect the lizards for the snakes. There have also been sightings of the fence lizards in northern Pennsylvania and southern New York (in the Hudson Valley and Long Island), suggesting that their range may be expanding north. Despite its broad geographic distribution, these lizards tend to prefer temperatures that optimize their digestive performance. Their locomotive performance is optimal at ranges of 28–38 °C and 25–36 °C. Regional variation The eastern fence lizard has several adaptations to better survive in colder regions of its distribution, including larger eggs, more efficient embryonic development, and shorter incubation times. The larger egg sizes are not a result of greater maternal investment — even when forcibly made smaller, efficiency and incubation time were similar to the originally larger eggs. On the other hand, female lizards in southern regions produce second clutches more often, although their clutches are smaller than northern ones. The season at which eggs can incubate and lizards may be active is longer in the southern regions. The overall reproductive success of both northern and southern lizards are approximately equal, given that all else (i.e. body size) is equal. Behavior and ecology When climate conditions are stable, fence lizards prefer to sleep in the same site over short periods of time. The site selected is within the lizard's home range or territory. When climate conditions are not stable, it has been found that some eastern fence lizards have been able to survive small frozen periods, and then return to normal after the period is over. Locomotion The running speed of these lizards is not limited by their mechanical power output. As the