Characteristics of nest soil, but not geographic origin, influence cold hardiness of hatchling painted turtles

We investigated environmental factors influencing cold hardiness in hatchli ng painted turtles (Chrysemys picta) indigenous to northeastern Indiana and the Sandhills of west-central Nebraska. In both locations, hatchlings over winter in their natal nests. Survival of hatchlings chilled to minimum temp eratures between -2.5 and -6.0 degreesC inside explanted natal nests ranged from 30 to 100%. Mortality likely was caused by freezing of the turtles th at was induced by contact with ice nuclei in the surrounding soil. Suscepti bility to inoculative freezing was strongly influenced by moisture content (7.5-25%, w/w) of the frozen soil in which hatchlings were cooled. When chi lled in soil containing 15% moisture, turtles from Indiana resisted inocula tive freezing better than hatchlings from Nebraska, but this variation was due to physical characteristics of the soils indigenous to each locale rath er than genetic differences between populations. Soil in which the Indiana turtles nested contained relatively higher amounts of clay and organic matt er. and bound more moisture, than the loamy sand at the Nebraska site. Soil collected from both locales contained potent ice nuclei that may constrain supercooling of the hatchlings, even in the absence of soil moisture. In a ddition to temperature and precipitation, local and regional variation in s oils is an important determinant of overwintering survival of hatchling C. picta. (C) 2001 Elsevier Science Ltd. All rights reserved.