Effect of Incubation Temperature on Development of Crocodylus johnstoni Embryos

Abstract

The pattern of growth in wet mass of Crocodylus johnstoni embryos is sigmoid and can be modeled with the logistic equation. The inflection point (time of maximum absolute growth rate) occurs when the incubation period is 77%-81% complete. Growth constants (r) from the logistic equation increase significantly with incubation temperature (T₁) over the range 28°-33° C, but asymptotic mass decreases. High-temperature embryos grow relatively more quickly but hatch at a lower yolk-free mass than at lower temperatures. Absolute growth rates (g · d⁻¹) are most sensitive to T₁ early in development, during the period of differentiation and organogenesis. Rates of late-term somatic growth show no consistent trend with T₁. Rates of morphological change (differentiation) defined by development rate coefficients also increase at higher T₁, but the temperature effect differs from that on rates of growth in mass. Thus the relationship between rates of differentiation and growth in size may alter with T₁. Shifts in the relative timing of significant differentiation and growth events may alter the relative sizes and functional capacities of tissues and organs. Such variation among hatchlings is likely to be implicated in the long-term influence of the incubation environment on posthatch survival and growth in crocodilians.