Modelling Development of Reptile Embryos under Fluctuating Temperature Regimes

Abstract

An increase in temperature, within bounds, will accelerate development of reptile embryos, and morphogenesis can be normal over a range of temperatures despite those varying rates of development. Less well understood is the form of the relationship that best describes variation in developmental rate with temperature. In this article, we apply a linear degree.hour model, an empirical curvilinear model, a biophysical model, and a polynomial model to data on rates of embryonic development and temperature in the pig-nosed turtle Carettochelys insculpta from northern Australia. The curvilinear models, which have been applied with success to development of insects, describe the embryonic development of turtles well. When fluctuating temperatures extend beyond the constant temperatures that support successful incubation, the curvilinear models continue to perform well, whereas the linear model predictions fail. Sensitivity analysis indicates that under some circumstances, incubation duration may be increased by diel temperature fluctuations, independent of an influence of mean temperature. In other circumstances, incubation duration may be decreased, and in still other circumstances, diel temperature fluctuations will have no impact on incubation duration. This adds an additional dimension to our understanding of how thermal regimes can be selected or manipulated by reptiles to optimise incubation duration and the timing of offspring emergence.

Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara?

“…Cycling soil temperatures were converted to a constant temperature equivalent (CTE) for each month, rather than a mean temperature, because CTEs are better predictors of offspring sex (Georges et al 2005). In brief, a CTE is calculated by first computing the amount of development completed at small, proportion of male hatchlings 0 0.05 These models assumed that eggs were deposited in unshaded sites 100 mm below the soil surface.…”

“…The temperatures and their corresponding developmental weightings are then ranked to determine a 'developmental median'-the temperature above which exactly half of the predicted development occurred (the CTE). We improved the resolution of our CTE calculations by integrating our hourly temperature predictions using a cubic spline, and we used a nonlinear development rate function (see §2f ) to predict development rates (refer to Georges et al 2005 for a detailed methodology). Because averaged monthly climate data were used to predict soil temperatures, we assumed a stable CTE for each month, from which we calculated daily development using the nonlinear development rate function described in §2f.…”

“…Degree-day functions do not produce realistic CTEs when temperatures cycle beyond the linear region of the temperature/ development rate function, so we developed a nonlinear function as recommended by Georges et al (2005). We used the programs DEVAR and DEVARA (Dallwitz & Higgins 1992) to respectively fit a linear-with-threshold (degree-day) function and various nonlinear (Dallwitz Higgins) functions to the S. punctatus data, with starting parameters b 1 Z0.06 and b 2 Z 12.5 (DEVAR) and b 1 Z0.8, b 2 Z13.0, b 3 Z25, b 4 Z6 and b 5 Z0.4 (DEVARA).…”

Mutual information reveals variation in temperature-dependent sex determination in response to environmental fluctuation, lifespan and selection

“…Because temperature varies in natural systems, the mean of temperature may not accurately predict clutch sex ratios (Georges 1989). For application to a particular TSD system, a different measure, such as a constant temperature equivalent (Georges 1989;Georges et al 2004Georges et al , 2005, may provide a better predictor of sex ratio and be the variable of interest for measuring intra-and interannual variation.…”

Effects of incubation temperatures on embryonic development in the Asian yellow pond turtle

“…In reptiles, temperature is an important ecological factor, and incubation temperature has been demonstrated to have profound effects on embryonic development and husbandry outcomes (Piña and Larriera, 2002;Georges et al, 2005). Significant data on the influence of incubation temperature on embryonic development are available in some turtles (Packard and Packard, 1988;Congdon and Gibbons, 1990;Booth, 1998;Grant et al, 2003), but no studies of the Asian yellow pond turtle have been undertaken.…”