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Biology 340 Comparative Embryology Lecture 2 Dr. Stuart Sumida. Phylogenetic Perspective and the Evolution of Development “Evo-Devo”. So, what is all the fuss about “phylogeny?” PHYLOGENETIC SYSTEMATICS allows us both define groups and their relationships.

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Biology 340

Comparative Embryology

Lecture 2

Dr. Stuart Sumida

Phylogenetic Perspective and the Evolution of Development

“Evo-Devo”


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So, what is all the fuss about “phylogeny?”

PHYLOGENETIC SYSTEMATICS allows us both define groups and their relationships.

However, those definitions MUST be careful, rigorous, and testable. (If they aren’t testable, they aren’t science.)


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Biologically valid groups must be defined on the basis of SHARED, DERIVED characteristics.

In other words: a biologically valid group is defined on the basis of features that are found in ALL members of the group, and ONLY in members of that group.

These SHARED, DERIVED characters are known as “SYNAPOMORPHIES.*”

*Singular: Synapomoprhy


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The degree of relatedness of groups is dependant on WHAT synapomorphies are shared,and at what level…

What is a shared, derived character at one level, will NOT be a shared derived character at another level.


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Bacteria Archaea Eucarya synapomorphies are shared,and at what level…


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Bacteria Archaea Eucarya synapomorphies are shared,and at what level…

So, these (Archaea and Eucarya) share more in common, and a more recent common ancestor.


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What kind of features can be used to generate phylogenetic trees?

They must be HOMOLOGOUS CHARACTERS. That is, they must be structures or features inherited from a common structure in a common ancestor.


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  • Criteria for Anatomical Homology: trees?

  • Same Anatomical Position

  • Same Embryological Material

  • (In animals) Supplied by Same Nerve

  • Function is NOT a good criterion (because functions can change over time…)


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From: trees?Chuck Amuck by Chuck Jones, Farrar Straus Giroux Publishers, New York, 1989.


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Knowing the relationships of organisms allows us to consider certain other concepts:

CONVERGENT EVOLUTION – the acquisiton of similar features due to similar environmental pressures.

PARALLEL EVOLUTION – (a special case of convergence) when convergent evolution takes place between very closely related lineages.


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Our focus certain other concepts:


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GERM LAYERS certain other concepts:

and

SEGMENTATION


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Eumetazoa has: certain other concepts:

Germ Layers

Endoderm

Ectoderm

Tissues


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Segmentation: an example: certain other concepts:

A simplified arthropod larva with multiple segments, each with appendages, or the genetic ability to develop appendages.


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Different kinds of arthropods can elaborate upon different segments and appendages. This provides an enormous versatility.


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Choanoflagella segments and appendages. This provides an enormous versatility.

Porifora

Placozoa

Ctenophora

Cnidaria

Protostomia

Pterobranchia

Echinodermata

Hemichordata

Chordata

Animalia


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Choanoflagella segments and appendages. This provides an enormous versatility.

Animalia


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Animalia segments and appendages. This provides an enormous versatility.

Multicellular heterotrophs


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Choanoflagella segments and appendages. This provides an enormous versatility.

Porifora

Metazoa


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Porifera (Sponges): segments and appendages. This provides an enormous versatility.

Known as far back as PreCambrian

600 million years ago.


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Example: Porifora (Sponges): No true germ layers or tissues segments and appendages. This provides an enormous versatility.


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Choanoflagella segments and appendages. This provides an enormous versatility.

Porifora

Placozoa

Ctenophora

Cnidaria

Eumetazoa


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Eumetazoa segments and appendages. This provides an enormous versatility.

Germ Layers

Endoderm

Ectoderm

Tissues


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  • Ctenophores and Cnidarians segments and appendages. This provides an enormous versatility.

  • Known as far back as PreCambrian “Ediacarian Faunas”.

  • Two germ layers – ectoderm and endoderm

  • Only one opening into gut.


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Ctenophores and Cnidarians segments and appendages. This provides an enormous versatility.

Known as far back as PreCambrian “Ediacarian Faunas”.


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Choanoflagella segments and appendages. This provides an enormous versatility.

Porifora

Placozoa

Ctenophora

Cnidaria

Protostomia

Bilateralia


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Bilateralia segments and appendages. This provides an enormous versatility.

Bilaterally symmetrical at some point during ontogeny

Three germ layers: ectoderm, endoderm, mesoderm.


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Bilateralia segments and appendages. This provides an enormous versatility.

Includes two great groups of animals:

Protostomia (means 1st mouth)

Deuterostomia (means 2nd mouth)


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Choanoflagella segments and appendages. This provides an enormous versatility.

Porifora

Placozoa

Ctenophora

Cnidaria

Protostomia

Pterobranchia

Deuterostomia


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Choanoflagella segments and appendages. This provides an enormous versatility.

Porifora

Placozoa

Ctenophora

Cnidaria

Protostomia

Pterobranchia

Echinodermata

Hemichordata

Chordata

Animalia


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Ecdysozoa segments and appendages. This provides an enormous versatility.

Others

Platyhelminthes

Mollusca

Annelida

Lophotrochozoa


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Ecdysozoa segments and appendages. This provides an enormous versatility.

Others

Platyhelminthes

Mollusca

Annelida

Lophotrochozoa


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Trilobitomorpha segments and appendages. This provides an enormous versatility.

Chelicerata

Crustacea

Myriapoda

Insecta

Ecdysozoa

ARTHROPODA

Mandibulata


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Choanoflagella segments and appendages. This provides an enormous versatility.

Porifora

Placozoa

Ctenophora

Cnidaria

Protostomia

Pterobranchia

Echinodermata

Hemichordata

Chordata

Animalia


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Recall Bilateralia segments and appendages. This provides an enormous versatility.

Protostomia (means 1st mouth)

Deuterostomia (means 2nd mouth)


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Choanoflagella segments and appendages. This provides an enormous versatility.

Porifora

Placozoa

Ctenophora

Cnidaria

Protostomia

Pterobranchia

Echinodermata

Hemichordata

Chordata

Animalia


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  • ECHINODERMATA: segments and appendages. This provides an enormous versatility.

  • Characterized by:

  • Radial symmetry as adults (bilateral as larvae)

  • Water-vascular system


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PHYLUM HEMICHORDATA: segments and appendages. This provides an enormous versatility.

Deuterostomes with GILL SLITS

(Original function of gill slits NOT for breathing; for FILTER FEEDING.)


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  • PHYLUM CHORDATA segments and appendages. This provides an enormous versatility.

  • Deuterostomes with the following synapomorphies:

    • Pharyngeal gill slits

    • Dorsal hollow nerve cord

    • Notochord

    • Post-anal tail


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  • PHYLUM CHORDATA segments and appendages. This provides an enormous versatility.

  • Includes the following subphyla:

    • Urochordata

    • Cephalochordata

    • Vertebrata

    • (People used to think Hemichordata were included, but they turn out to be the sistergroup.)


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SUBPHYLUM UROCHORDATA segments and appendages. This provides an enormous versatility.


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How can something like this be related to chordates like us? segments and appendages. This provides an enormous versatility.

Addition of a new life stage: a mobile larval stage.

CAENOGENESIS: Interpolation of a new life stage into the lifecycle.


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The new larval stage of a urochordate segments and appendages. This provides an enormous versatility.


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UROCHORDATE: Metamorphosis from larva to adult segments and appendages. This provides an enormous versatility.


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Adult urochordate segments and appendages. This provides an enormous versatility.


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Some urochordates stay larval all life long, but they become sexually mature – an example of NEOTONY.


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More “fish-like” sexually mature – an example of PHYLUM CEPHALOCHORDATA


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So, then what’s a vertebrate…? sexually mature – an example of


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“Fishes” including Most Synapsida Reptilia

Sarcoptrygians Amphibians Diadectomorpha (Mammals) (including Aves)

AMNIOTA (FOR SURE)

Amniota?

TETRAPODA


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  • Diadectomorpha: outside the embryo to help it survive:

  • No intertemporal bone like other amniotes

  • Very terrestrially adapted


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outside the embryo to help it survive:Amphibia” Amniota

Seymouriamorpha Diadectomorpha Synapsida Parareptilia Captorhinidae Diapsida Archosauromorpha

Reptilia

Amniota



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Synapsida: side of skull Including Modern Mammals


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AMNIOTA side of skull

Diadectomorpha(?)Synapsida Reptilia Avialae

Mammalia

“Therapsida”

“Pelycosauria”

The Synapsida can be divided into three “grades.”


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  • Mammals: side of skull

  • Mammary glands

  • Hair

  • Facial muscles – muscles of facial expression

  • A specialized jaw joint (between a single bone of the lower jaw (dentary) and the squamosal region of the skull)

  • Three bones in the middle ear to help in hearing


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Mammals have mammary glands for side of skullNOURISHING THE YOUNG

Mammals have HAIR.



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Monotremata Metatheria Eutheria

(Egg-laying mammals) (Marsupials) (Placental Mammals)

Theria

Mammalia (detail)


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The duck-billed platypus and spiney anteater ( EutheriaEchidna) are members of Monotremata (egg-laying mammals).


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Monotremata EutheriaMetatheria Eutheria

(Egg-laying mammals) (Marsupials) (Placental Mammals)

Theria

Mammalia

Metatheria: also known since the Cretaceous


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Monotremata EutheriaMetatheria Eutheria

(Egg-laying mammals) (Marsupials) (Placental Mammals)

Theria

Mammalia


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The EutheriaMETATHERIA, also known as MARSUPIALS are often called the “pouch mammals” because although initial development is internal, much takes place in the mother’s pouch – which is technically outside the body.


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  • A Placenta: Eutheria

  • Combination of the amniote Chorion and Allantois

  • Helps the developing embryo to communicate with mother.


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EutheriaEvo-Devo”

The Union of Evolutionary and Developmental Biology

Natural for evolutionary biologists and developmental biologists to find common ground. Evolutionary biologists seek to understand how organisms evolve and change their shape and form. The roots of these changes are found in the developmental mechanisms that control body shape and form.


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Darwin's perception was given a theoretical basis and evo-devo its first theory when Ernst Haeckel proposed that because ontogeny (development) recapitulates phylogeny (evolutionary history), evolution could be studied in embryos.

Technological advances in histological sectioning and staining made simultaneously in the 1860s and 1870s enabled biologists to compare the embryos of different organisms.

Though false in its strictest form, Haeckel's theory lured most morphologists into abandoning the study of adult organisms in favor of embryos--literally to seek evolution in embryos.


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Notice how ontogenetically early forms appear more similar. evo-devo its first theory when Ernst Haeckel proposed that because ontogeny (development) recapitulates phylogeny (evolutionary history), evolution could be studied in embryos.


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The idea that ontogeny recapitulates phylogeny suggests that an organism's development will take it through each of the adult stages of its evolutionary history, or its phylogeny. Thus its development would reiterate its evolutionary history — ontogeny recapitulating phylogeny.

This idea is an extreme one. If it were strictly true, it would predict, for example, that in the course of a chick's development, it would go through the following stages: a single celled organism, a multi-celled invertebrate ancestor, a fish, a lizard-like reptile, an ancestral bird, and then finally, a baby chick.


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What is clear is that we cannot only study evolution by looking at a progression of adult structures.

Adult x+n

Adult 4

Adult 3

Adult 2

Adult 1


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We must study the evolution of ontogenies. looking at a progression of adult structures.

Embryo x + n

Embryo 4

Embryo 3

Embryo 2

Embryo 1

Adult x+n

Adult 4

Adult 3

Adult 2

Adult 1

Useful characters for understanding the evolution of organisms/groups can come from any ontogenetic stage.


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