Biology Reference
In-Depth Information
CHAPTER
11
Evolutionary Developmental Biology (1):
The
Evolution of Onto
geny
Studies of evolving ontogenies are grounded in two important insights. The first is that
all evolutionary change arises from changes in ontogeny and therefore we need to under-
stand how ontogenies evolve in order to understand the origins of morphological diver-
sity, i.e. disparity (
Zelditch et al., 2003b; Adams and Nistri, 2010; Drake, 2011; Frederich
and Vandewalle, 2011; Gerber, 2011; Ivanovic et al., 2011; Piras et al., 2011
). What modifi-
cations of ontogeny are responsible for the disparity of a group, and whether those modifi-
cations increase or decrease disparity can be answered by comparative analysis of
ontogenies. As found in a study of damselfishes, disparity of both body shape and diet
increase over ontogeny (
Frederich and Vandewalle, 2011
). But disparity of body shape
decreases over ontogeny despite an increase in disparity of diet in piranhas (
Zelditch
et al., 2003b
). In European cave salamanders, foot shape and interdigital webbing both
decrease in disparity over ontogeny because some species maintain a webbed juvenile foot
(and juvenile foot shape) as they grow whereas others increase webbing and change foot
shape as they grow; the result is similar adult morphologies via different developmental
processes (
Adams and Nistri, 2010
). By combining comparative studies of ontogeny with
analyses of disparity at two or more developmental stages, it is possible to test hypotheses
about the developmental origins of disparity.
The second insight is that organisms have time-extended phenotypes. An organism's
phenotype is not static
it changes from age to age in both form and function. To com-
prehend that dynamic form and function relationship, as it evolves, we need to under-
stand how developing organisms negotiate the ontogenetic transformations in form and
function. Several studies have examined the relationship between ontogenetic transforma-
tions in shape and measures of performance such as bite-force or biomechanical para-
meters such as mechanical advantage of the masticatory apparatus (
Birch, 1999; Abdala
et al., 2001; Pfaller et al., 2010
; Tanner et al., 2010b;
La Croix et al., 2011a,b
). For example,
studies of carnivores found that feeding performance matures far later than skull size,
