Ernst Heinrich Haeckel (1834-1919) Influential German evolutionist ...

Ernst Heinrich Haeckel (1834-1919)
Influential German
evolutionist, morphologist,
and developmental biologist.
He argued that "ontogeny
recapitulates phylogeny"
and therefore that
phylogeny should be
reconstructed on the sole
basis of ontogeny.

Wilhelm Roux (1850-1924)
“….conclusions drawn from the
investigation of individual
development throw light on the
phylogenetic processes.”

Richard Owen (1804-1892)

Charles Darwin (1809 –1882)
“Unity of Type” vs. “ Conditions of Existence”
“Common ancestor” vs. “ Descent with modification”

Figure 23.1(1) Relationships among Phyla

The search for the Urbilaterian ancestor
Sean Carroll 1997
—“paleonotology without fossils”
—find homologous genes that are performing the same functions
in both a deuterostome and a proteostome.
Examples:
1. Pax6 protein in eye development;
2.tinman/Nkx2-5 in heart formation;
3.transcription factor in head formation.
4. anterior-posterior polarity based on Hox gene expression.

Extopic expression of Pax6
induce eye formation

Figure 23.2 Expression of Regulatory Transcription Factors in Drosophila and in
Vertebrates Along the Anterior-Posterior Axis

Figure 9.28 Homeotic Gene Expression in Drosophila

Hox genes: Descent with modification
Slack et al (1993) - Hox gene expression pattern defines the development of all
animals and that that pattern of Hox gene expression is constant for all phyla.
Ways of modification:
1. Changes in the Hox protein responsive elements of down stream genes;
ex: fly’s halteres & butterfly’s hindwings; Ultrabithorax (Ubx);
2. Changes in Hox gene transcription patterns within a region of the body;
ex: abdominal prolegs in caterpillars; Distal-less (Dll)
3. Changes in a Hox gene that give its protein new properties;
ex: why arthropods varies in the numbers of legs?
Ubx and Dll interaction is changed in the insect group.
4. Changes in Hox gene transcription patterns between regions of the body;
Ubx and abdA interaction in determine formation of locomoter limbs and
feeding appendages.
5. Changes in the number of Hox genes;
**mutation in the Hox gene can produce “Atavistic” condition—the organism
resembles an earlier evolutionary stage.

Figure 23.3 Differences in Larval and Adult Morphology Due to Hox Gene Differences

Figure 9.29 A Four-winged Fruit Fly Constructed by Putting Together Three
Mutations in cis Regulators of the Ultrabithorax Gene

Figure 23.4 Distal-Less Gene Expression in the Larva of the Buckeye Butterfly, Precis

Figure 23.5(1) “Holes” in the Expression of abdA and Ubx in the Abdomen
of the Larval Butterfly Precis

Figure 23.5(2) “Holes” in the Expression of abdA And Ubx in the Abdomen
of the Larval Butterfly Precis

Figure 23.6(1) Changes in the Ultrabithorax Protein Associated with the Insect Clade

Figure 23.7(1) Hox
Gene Expression and
Morphological
Change in
Crustaceans

Figure 23.8 Schematic Representation of the Expression of Ubx and abdA (Green) in the
Thoracic Segments of Different Types of Crustaceans

Figure 23.11 Postulated Ancestry of the Hox Genes From a Hypothetical Ancestor

Figure 23.10 Representation of Skeletal Elements:
exmple of atavistism

Figure 23.13 Three Modifications of the Wnt Pathway
Homologous pathways of development

Figure 23.15 Homology of Signaling Pathways in the Formation of the Anterior-Posterior
Axes in Drosophila and Chick Appendages

Figure 23.16 Deep Homology of the Limbs

Figure 23.17 Allometry and Modularity in the Vertebrate Eye

Modularity
Modularity allows three processes to alter development:
(1) Dissociation:
Heterochrony: shift in the relative timing of two developmental
process
ex: 1. eye development in reptile;
2. larval stage in salamanders;
Allometry: different part of the organism to develop in different rate;
important in forming variant body plans within a phylum
ex: toes of horse;
(2) Duplication and divergence
(3) Cooption: one gene for multiple function.
ex: 1. engrailed and distal-less to form eyespot in butterfly wing
2. jaw part become middle ear in mammals

Figure 23.18 Heterochrony in Bolitoglossa Can Create a Tree-Climbing Salamander

Figure 23.19 Allometric Growth in the Whale Head

Figure 23.20 Co-Option of Signal Transduction Pathways in the Formation
of Butterfly Eyespots

Figure 23.21(1) Evolution of the Mammalian Middle Ear Bones From the Reptilian Jaw

Figure 23.21(2) Evolution of the Mammalian Middle Ear Bones From the Reptilian Jaw

Generation of evolutionary novelty
Accumulation of small genetic changes
OR
Combining existing part in new ways rather than creating new parts
(Francois Jacob, 1977)

Figure 23.22 Regulation of Chick Limb Apoptosis by BMPs

Figure 23.23(1) Expression Patterns of BMP2 and Shh in Feathers and Scales

Figure 23.23(2) Expression Patterns of BMP2 and Shh in Feathers and Scales

Figure 23.24 GIS Analysis of Gene Activity in the Formation of the First Set
of Cusps in Mouse and Vole Molars

Figure 23.25(1) Basic Model for Cusp Development in Mice and Voles

Figure 23.25(2) Basic Model for Cusp Development in Mice and Voles

Figure 23.26 Neural Crest Cell Migration Patterns in Lampreys and Gnathostomes

Developmental constraints
1. physical constrains
2. morphogenetic constraints
--reaction-diffusion model to explain limb formation.
3. phyletic constraints
Gould and Lewontin, 1979”once a structure comes to be generated by
inductive interactions, it is difficult to start over again.”
--the phylotypic stage of embryo development
** Cannalization:
buffering capacity of organism;
new mutations do not alter development;
through gene redundancy.

Figure 23.27 Relationship Between Cell Number and Number of Digits in Salamanders

Figure 23.28 Mechanism for the Bottleneck at the Pharyngula Stage
of Vertebrate Development

Figure 23.30 A Newly Emerging Evolutionary Synthesis