Biology Reference
In-Depth Information
formalism requires that the same shapes appear in the ontogenies of all species being com-
pared, just at different ages/sizes. So we need an alternative formalism that can be used
when species follow species-specific ontogenetic trajectories.
Gould (1977; pp. 385
388)
sug-
gested one such alternative, which is to compare the rates and timings at which species depart
from their own juvenile forms, an approach similar to that used by Hingst-Zaher and collea-
gues (
Hingst-Zaher et al., 2000
), who measured the amount of shape change from age to age
by the Procrustes distance between successive ages. They showed that the distance declines
with age, meaning that the rate of development (like that of growth) decreases over time. To
linearize the relationship between size and age, they regressed size on log(age
1) and the
same transformation can be used to examine the relationship between development and age
(
Figure 11.23
). By linearizing the relationship between shape and age, we can compare the
developmental rates, which are 0.061 for the house mouse and 0.044 for the cotton rat.
1
FIGURE 11.23
A linear regression of the Procrustes distance between each specimen and the mean of the
youngest age class on log (age
1). (A) House mice; (B) cotton rats.
1
