Separating the Effects of Vapor Pressure and Heat Exchange on Water Exchange by Snapping Turtle (Chelydra serpentina) Eggs

When turtle eggs are incubated on media at different water contents, both the water potential and thermal conductivity of the medium change. Snapping turtle eggs were incubated fully buried in sand at constant water content (θ, 4% by mass) but different water potentials (ψ) to assess the effect of ψ on egg water exchange independent of medium thermal conductivity (k). Treatment ψs were fixed using an isopiestic technique. Over the course of incubation, change in fractional egg mass was positively correlated with Ψ. Total egg water exchange ranged from 0.0 to +0.5 g × g⁻¹ of initial egg mass for viable eggs. Hatching success averaged 0.94 for the four highest Ψs but decreased for the two lowest Ψs. Hatchling and yolk mass were independent of water exchange above egg mass gains of +0.1 g × g⁻¹ (Ψs ≥ −542 kPa) but decreased for egg mass gains less than +0.1 g × g⁻¹ (Ψs < −542 kPa). Hatchling and yolk water content and incubation period were independent of egg water exchange for all treatments. The results are consistent with the hypothesis that the thermal conductivity of the incubation medium influences the water exchange of eggs.

Fig. 1.

The change in mass of snapping turtle (Chelydra serpentina) eggs incubated in sand at−7 kPa (A) and −188 kPa (B). The upper and lower curves represent the 95% confidence limits for the (central) 3° polynomial regression model, fitted to the data as described in the text

Fig. 2.

The 3° polynomial models from the each of the six treatment groups compared. The fit of the model to the dataset as see in Figure 1 is about the same for each treatment

Fig. 3.

The influence of total egg water exchange (g × g^-1) of initial egg mass on hatchling wet mass. (A) presents all the data. (B) presents data truncated above a total water exchange of + 0.1 g × g^-1. The curves represent linear regression models and their associated 95% confidence intervals

Fig. 4.

The influence of total egg water exchange (g × g^-1) of initial egg mass on hatchling wet content (A) and incubation period (B). Linear regression models (together with the 95% confidence limits on the model) are shown for the respective datasets

Fig. 5.

The influence of total egg water exchange (g × g^-1) of initial egg mass on hatchling yolk (A) and hatching success (B) in various treatments as a function of total water uptake

Received: 14 Jun 2001

Accepted: 22 Mar 2002