Heterochrony Within Species: Craniofacial Growth in Giant, Standard, and Dwarf Rabbits

Abstract

Change in developmental timing is one source of heritable variation upon which selection can act. However, the amount of variation possible in ontogenetic trajectories is often unknown. We used three different-sized conspecific breeds of domestic rabbits to investigate the extent of variation in growth trajectories of craniofacial morphology. The growth and adult morphology of several structures (one soft tissue and 15 skeletal) were quantified and analyzed. We took two views of radiographs at close time intervals throughout ontogeny, from one week of age through adult size. Measurements from the radiographs were analyzed using a Gompertz growth model. Between-breed differences in model parameters were tested using one-way ANOVA. Few significant differences existed between the white and giant rabbits, but several differences were found between the white and dwarf breeds. Similarly, comparisons of adult morphology showed that white and giant rabbits are the same shape, while dwarf rabbits have shorter and broader snouts than white rabbits. The variation in size among breeds appeared to be due to differences in the length of time spent growing at rates near the maximum growth rate. While no one parameter of this model quantifies this pattern, differences in duration of maximum growth rate can be seen in the first derivative of the growth trajectory. Small changes in the model's parameters that measure rate and timing of growth have large morphological consequences, indicating that heterochronic changes are important sources of variation.

Sources of variation in the long-distance vocalizations of spotted hyenas

“…Ontogenetic variation in minimum fundamental frequency revealed a pattern similar to that for chest girth (N = 251; Figure 2a,b), suggesting that body size might influence vocal pitch. In both sexes, the development of chest girth and minimum fundamental frequency strongly conformed to the German Gompertz model for biological growth (Fiorello & German, 1997;Zelditch et al, 2003; Table 1). The asymptote of the model for male minimum fundamental frequency was greater than the respective asymptote for females, and the asymptote for chest girth among males was less than that among females.…”

Molecular heterochrony in the early development of Drosophila

“…[31][32][33][34][35]. However, Raff (15) has pointed out that heterochrony can be found in earlier as well as in later stages of development.…”

Post-weaning maternal effects and the evolution of female dominance in the spotted hyena

“…The formula used was xðtÞZ Af1Kexp K ðt 0 KtÞg, where x(t) is the measurement of interest at time t; A is the asymptotic adult value; K is the rate of approach to adult value; and t 0 is the age at which growth begins (Gaillard et al 1997;Zelditch et al 2003). For hindfoot length and ingestion time, the best-fitting model was the Gompertz growth model (as parametrized by Fiorello & German 1997): x(t)ZA e KkeKbt , where k is the initial growth rate and b is the decay of the growth rate ( Fiorello & German 1997;Zelditch et al 2003). We designated 95 per cent of the asymptotic value as age at maturity, and present the percentage of mature size or feeding performance achieved at each of five ages: 0, 8, 13, 24 and 36 months, based on the predicted values at each age from the fitted growth curve.…”