The Allometry of Reproduction: An Empirical View in Salamanders

In order to distinguish important variations in some life history traits, body size must be subtracted by constructing allometric null hypotheses. We present interspecific empirical models that describe the relationship among salamanders between body size and three variables: clutch volume, clutch size, and egg size. The relationship between log clutch volume and log body volume for 74 species of salamanders has a correlation of .899 and a slope of 0.64. The significance of this interspecific slope and lack of identity between it and intraspecific slopes is discussed. The relationships between log clutch size versus log body volume and log egg volume versus log body volume are largely determined by the mode of reproduction of the species. Data for four populations of salamanders of the genus Ambystoma are presented and compared with the models. The usefulness and necessity of first determining how a particular reproductive trait is expected to change with body size is made clear, for example, by observing that individuals of two of the populations studied have the same percent of their body volumes occupied by ova. In comparing the two populations with the empirical model, however, individuals are shown to contain very different clutch masses relative to what is expected for salamanders of their respective sizes. Constraints of size and shape must be considered in order to properly evaluate reproductive adaptations.