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 Developmental Biology Influence in Evolutionary Biology Molecular approaches allow study of developmental mechanisms within comparative evolutionary context Development shown to depend upon gene expression

Millions Years Ago How to Make an Organism Reptile Amphibian Fish Agnathan Ontogeny recapitulates phylogeny

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)

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

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

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

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

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

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 ( ) Macromutational Hypothesis

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?

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

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

paedomorph metamorph Wild Strain Proportion Lab Strain

Segregation of contig325 genotypes Cross TypeLCMHetHom Lab Met 52 5 Paed 2 39 Wild 1 Met Paed 1 16 Wild 2 Met Paed1 41

Continuous variation in metamorphic timing Wild 2 Cross

contig325 contributes to continuous variation Wild 2 Cross

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

Evolution in the Fossil Record Chapter 4

The Earth is Old

The Geological Time Scale is Based Upon the Principles of Relative Dating Younger rocks are deposited on top of older rocks Lava and sedimentary rocks were originally laid down in a horizontal position Boulders or cobbles found in a body of rock are older than their host rock Earlier fossil forms are simpler than more recent forms, and more recent forms are most similar to existing forms.

Geologic Column Earth’s history as told by rock strata

The Geologic Time Scale Chapter 4, p. 70

Fossils and associated rocks contain reactive elements that decay at known rates Uranium > Lead 235 = 7 x 10 8 years Carbon 14 --> Nitrogen 14 = 5730 years Parent Atom Daughter Atom Half-life Radiometric Dating

Time (half-lives) Surviving Parent Atoms Accumulating Daughter Atoms /1 1/3 1/7 Radioisotope Decay 1. Find fossil 2. Determine ratio of parent to daughter atoms 3. Determine number of elapsed half-lives 4. Estimate age of fossil

You are using C 14 (half-life = 5730 years) radioisotope dating to determine the age of rocks associated with a fossil. The percentage of daughter isotope atoms (N 14) ) is 87.5%. What is the age of the fossil? Try this problem 17,190 yrs