The Water Exchange and Hydric Microclimate of Painted Turtle (Chrysemys picta) Eggs Incubating in Field Nests

Publisher Website
Google Scholar
Abstract
Freshly laid eggs of the painted turtle, Chrysemys picta, were located in northwest Iowa during the summers of 1985 and 1986. The eggs were weighe djust after laying and periodically throughout incubation. Near the expected time of batching, the eggs were removed from their nests and allowed to hatch in the laboratory, where hatchling wet and dry mass were measured. Soil water potential during incubation was measured with tensiometers placed near the nest. Soil water content was measured for a soil profile close to the nest. Nest temperatures were measured throughout incubation. On average, 12 eggs per clutch were laid, with an average initial egg mass of 6 6g. The eggs typically demonstrated constant increase in mass with time. The average daily water uptake ( ) was around 19-35 mg.d⁻¹. The average mass gain uwas 33% of initial mass over the period of measurement. Hatchling wet and dry mass were influenced by initial egg mass and by the duration of incubation but not by the quantity of water exchanged or by position in the nest. Water potential in the soil surrounding the nests averaged-29 kPa (±21 SD) and ranged from-0 kPa to-77 kPa. The soil column was typically drier in the top 4 cm (>-100 kPa) and at relatively constant wetness (approx.-10 to-50 kPa) from 5 to 20 cm below the surface. The tops of all nests were deeper than 4 cm and the nests averaged 5 cm from top to bottom. Maximum and minimum nest temperatures averaged 27°-29° C and 20°-21° C, respectively. There was a temperature difference between the top and bottom of the nest. The magnitude and pattern of egg mass changes of Chrysemys eggs infield nests are differentfrom those observed in the laboratory. These differences are likely due to the differences between the hydric and thermal environments of the field nest and those used during incubation in the laboratory.