Annual and local variation in reproduction in the red-eared slider Tucker, J. K., G. L. Paukstis, and F. J. Janzen. 1998. Annual and local variation in reproduction in the red-eared slider, Trachemys scripta elegans. Journal of Herpetology 32(4):515 526. Reprinted by U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin, April 1999. LTRMP 99-R006. 12 pp. (NTIS #PB99-152183) ABSTRACT We studied variation in reproductive traits among 789 red-eared sliders (Trachemys scripta elegans) from three sites in west-central Illinois from 1994 to 1996. Overall, mean clutch size ranged between 12.5 and 15.1 eggs, mean egg mass per clutch ranged between 10.03 and 11.68 g, and mean relative clutch mass (clutch mass/spent body mass) ranged between 0.079 and 0.097 for nine site-year cohorts. Maternal body size was the most important source of variation in all measures of reproduction because larger females laid larger eggs and larger clutches than smaller females. Reproductive output independent of body size was greater in 1995 than in 1994 or 1996. Clutch size and egg varied similarly among years at each site. Overall, clutch mass in 1995 was 15.8% and 17.8% greater than clutch mass in 1994 and 1996, respectively. This variation in reproductive output was primarily due to changes in egg number rather than changes in egg size, consistent with theories of egg optimality. Turtles at one site produced relatively small but relatively more eggs per clutch than turtles from the other two sites. This pattern persisted despite varying amounts of energy devoted to reproduction from year to year. However, an egg size- clutch size trade-off could only be weakly demonstrated among nine site-year cohorts. Geographic variation was confirmed for clutch size, which decreased with decreasing latitude, but not for egg mass and plastron length. KEYWORDS Clutch mass, clutch size, Illinois, latitude, optimal egg theory, red-eared slider, reproduction, Trachemys scripta elegans