Incubation Time and Rate of Embryonic Development in Amphibians: The Influence of Ovum Size, Temperature, and Reproductive Mode

Incubation time in amphibians can be mathematically partitioned into two other parameters as follows: Incubation time = rate of embryonic development⁻¹ X protraction of development. The latter parameter is important because it reflects the degree of development of the embryo at hatching. Protraction of development is defined as the ratio of incubation time to time taken to reach a neurula stage common to all amphibians, and it is directly correlated with Gosner stage at hatching in anurans (n = 30 species). This analysis assesses the influence of two covariates, ovum size and temperature, on the three parameters above for two orders of amphibians, anurans and caudates. The ANCOVA of 55 species in 17 families shows that incubation time scales to ovum volume0.444 · e−0.121 temp (multiple R2 = 0. 88), rate ofdevelopment scales to ovum volume0.435 · e0.115 temp (multiple R2 = 0.90), and protraction of development is not significantly related to either ovum volume or temperature. Ovum volume is inversely related to temperature, although r² is small (0.26). Incubation time of caudates is 2.47 times that for anurans for a given ovum volume and temperature. This difference can be attributed to both a slower rate of embryonic development in caudates than anurans (factor = 0.71) and a greater protraction of embryonic development (factor = 1. 76). This analysis provides a basis for evaluating the influence of reproductive mode onparameters of embryonic development. Examples are drawn from amphibians that breed in ephemeral bodies of water and amphibians that breed on land.