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

3. Millions Years Ago How to Make an Organism Reptile Amphibian Fish Agnathan 0 325 500 600 Ontogeny recapitulates phylogeny

4. 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

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

6. 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. Karl Ernst von Baer’s Law

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

8. 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 Heterochronies can be defined at all levels

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

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

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

12. Allometry of skull and brain

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

14. A. mexicanum Richard Goldschmidt (1878-1958) Macromutational Hypothesis

15. Questions 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?

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

17. Interspecific crosses using A. t. tigrinum and A. mexicanum

18. 0.00 0.25 0.50 0.75 1.00 paedomorph metamorph Wild Strain Proportion 571 57 82 73 Lab Strain

19. Segregation of contig325 genotypes Cross TypeLCMHetHom Lab Met 52 5 Paed 2 39 Wild 1 Met 60 35 Paed 1 16 Wild 2 Met 219 196 Paed1 41

20. Continuous variation in metamorphic timing Wild 2 Cross

21. contig325 contributes to continuous variation Wild 2 Cross

22. Contig325: also contributes to continuous variation. Time Hatching Metamorphosis Paedomorphosis