Developmental Biology Influence in
Evolutionary Biology
1860
1900
2000
Darwin: “embryology is to me by far the strongest single class of facts in favor of a change of forms”.
Rise of experimental embryology vs genetics
Development shown to depend upon gene expression
Molecular approaches allow study of developmental mechanisms within comparative evolutionary context

Ontogeny recapitulates phylogeny
0 325 500 600
Millions Years Ago

Haeckel:
Development is a guide to understanding Evolution
- Descendants pass through the developmental stages of their ancestors
- New stages are added on to the end of ontogeny
- Earlier stages are condensed or lost over time

Bad Theory Can Kill: Case of the Emperor Penguin
(Robert Scott’s Expedition to South Pole)

Karl Ernst von Baer’s Law
Features common to a group of related taxa often appear in development before the specific characters of the more recently evolved taxa of the group.

Heterochrony: Dissociation of the relative timing of events in development between ancestral and descendant ontogenies.

Heterochronies can be defined at all levels
Global Heterochronies: At the level of the organism
Classical heterochrony relating development of somatic tissue to germ tissue
Local Heterochronies: At the level of individual traits
- Isometric Growth
- Allometric Growth
- Molecular heterochronies

Two general types of Heterochrony:
1) Paedomorphosis
2) Peramorphosis

Paedomorphosis
A
D progenesis
A neoteny
D
A
D post-displacement
Reproductive
Peramorphosis
D
A hypermorphosis
D acceleration
A
D
A predisplacement

Peramorphosis: Developmental extension/elaboration of the adult stage of the ancestral species, in the descendant.

Allometry of skull and brain

Paedomorphosis: Expression of juvenile, ancestral features in the adult stage of a descendent species.

A. mexicanum
Richard Goldschmidt
(1878-1958)

1. Do alternate life cycle modes evolve via genetic changes in developmental timing?
2. What is the relationship between discrete and continuous variation in developmental timing?

Evolution of developmental timing: metamorphosis vs paedomorphosis
Hatching
Time
Metamorphosis
Paedomorphosis

1.00
0.75
0.50
0.25
0.00
82
73
Lab Strain metamorph paedomorph
57
571
Wild Strain

Cross Type LCM Het Hom
Lab
Wild 1
Wild 2
Met
Paed
Met
Paed
Met
Paed
52
2
60
1
219
1
196
41
35
16
5
39

Wild 2 Cross

contig325 contributes to continuous variation
Wild 2 Cross

Hatching
Time
Metamorphosis
Paedomorphosis