Which Of The Following Features Is A Synapomorphy Of The Animals?

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Lecture 6

THERE IS ASSIGNED HOMEWORK

CLADISTICS

HOW, IN Particular, Practise We Work OUT RELATIONSHIPS?

There are several methods that have been used to piece of work out the evolutionary relationships of organisms. The most successful of these is the so-called "cladistic" or "phylogenetic" method. This method is based on an older concept, that of "homologous characters".

To begin, we supply some definitions:

Graphic symbol:
A characteristic or thing we can examine or label. It is of import that the characteristic be heritable.
Homologous Character:
Character which is shared past taxa by descent.
Coordinating Character
Shared resemblance betwixt characters by other ways than descent, such as adaptation. This is often called a homoplastic character.

Homologous characters are the key basis of cladistics. In cladistics we await for characters that nosotros tin can hypothesis are shared considering they were inherited from a common ancestor. The premise is that a species develops a new character and passes that character down to its girl species. Each of the daughter species and so can add new characters, but each adds a dissimilar one, since they are at present separate species and on their own evolutionary trajectory. This continues to happen through fourth dimension as more and more species dissever off.

We see in retrospect characters shared between two species. How do we decide if a character is homologous or coordinating?

First we hypothesize them to be so. Then nosotros look at the preponderance of other characters to test our hypothesis. Cladistics gives us a framework in which to practice this. Cladistics was basically invented by Willi Hennig who was a specialist in flies. Here is a link to a site that describes in detail and in a dissimilar way how we do cladistics: http://www.ucmp.berkeley.edu/clad/clad1.html

In cladistics we presume that we wish to focus on genealogical relationships and that our classifications of taxa should depend on our assay of these genealogical relationships. Of prime importance is the historical sequence in which the taxa descended from a common ancestor. Hence, our cladistic hypotheses are based on our estimate of the historical sequence of the acquisition of novel characters.

Next, some more definitions:

Primitive Graphic symbol = Plesiomorphy
A graphic symbol which is in the state shared by the mutual ancestor of the group.
Derived Character = Apomorphy
A grapheme in a new state, non the primitive one.
Shared Character:
A character shared by all the members of the grouping.
Shared Derived Character = Synapomorphy
A character which is in a new state and shared by all the member of the grouping.
Unique Derived Character = Autapomorphy
A character constitute just in that taxon. Is a synapomorphy when discussed at the level of the members of a taxon.

The method in cladistics is to build and test relationships based on the distribution of the states of characters and to build groups by the recognition of synapomorphies.

Permit´s look at a specific instance of a cladogram

VERTEBRATES
CICHLID -
has backbone, paired appendages (fins), dorsal nerve cord and aorta which are shared derived characters uniting the cichlid with frogs, turtles, kangaroos, mice, and humans.
FROG -
has all those plus legs.
TURTLE -
has all those plus a difficult shelled egg called an amniotic egg.
KANGAROO -
all those plus hair, warm claret, and egg develops inside.
MOUSE -
all those plus placental development
HUMAN -
all those plus very large brain and loss of pilus.

NOTE THAT FOR EACH SHARED DERIVED Graphic symbol At that place IS A PRIMITIVE Grapheme.
For example, kangaroos, mice and humans all share having hair. The respective primitive graphic symbol is "not having hair". Fish, frogs and turtles lack hair, merely these shared primitive characters are non show of relationship, because many other organisms lack pilus that are outside the group we are considering - clams, for example.
NESTED SETS OF SHARED DERIVED CHARACTERS ARE DEPICTED ON THE CLADOGRAM OF THESE SYNAPOMORPHIES ALONG WITH THEIR CORRESPONDING SHARED Primitive CHARACTERS.
Cladogram:
A branching diagram depicting the hierarchical arrangement of taxa divers by the distribution of shared derived characters.
But there are also characters which are unique to each group (autapomorphies), non shared with the others
CICHLID -
symmetrical tail fin, spiny fins.
FROG -
long sticky tongue, tadpole.
TURTLE -
shell covering torso, no teeth.
KANGAROO -
big grinding teeth, thick tail.
MOUSE -
ever-growing incisors.
Human -
opposable thumb, reduced toes, huge brain.

WE Tin PUT THESE CHARACTERS ON A CLADOGRAM AS WELL.
AND, There ARE CHARACTERS THAT Brand NO SENSE AT ALL IN THE Fix OF RELATIONSHIPS Nosotros Accept PRESCRIBED Here. THESE ARE HOMOPLASTIC CHARACTERS, MANY OF WHICH ARE Analogous CHARACTERS Also.

CICHLID -
thin scales (shared with turtle and mouse).
FROG -
no scales (shared with mammals merely non turtle).
TURTLE -
reduced teeth (shared with man).
KANGAROO -
bipedal (shared with man) - big ears (shared with mouse).
MOUSE -
scales on tail (shared with turtle).
Human -
no tail (shared with frogs).

IF WE PUT THESE CHARACTERS ON THE CLADOGRAM, You lot CAN Encounter HOW THEY DO NOT Brand A CLEAR PATTERN.
A KEY FEATURE OF THE CLADISTIC METHOD IS THAT Information technology ALLOWS TESTING BY THE HYPOTHETICO-DEDUCTIVE METHOD

So we could have used some of these characters to group the taxa, but and then the characters that we used as shared derived characters would take to be explained abroad past ad hoc explanations. Each advertizing hoc explanation makes the proposed hypothesis more and more than untenable. If the number of characters that have to be explained away by advertising hoc explanations gets larger than the number of shared derived characters that support the cladogram, the hypothesis (i.eastward. cladogram) should exist rejected.
MUST Be BUTTRESSED BY More SHARED-DERIVED CHARACTERS - OR HYPOTHESIS MUST Get

Similar ALL OF Scientific discipline

A Fundamental FEATURE OF CLADISTICS IS THAT GROUPS OF ORGANISMS ARE DEFINED Past SYNAPOMORPHIES. THESE ARE MONOPHYLETIC GROUPS. At that place ARE OTHER KINDS OF GROUPS, THOUGHT TO Be MUCH LESS DESIRABLE By CLADISTS, THAT ARE DEFINED Past HAVING MEMBERS SHARING OTHER KINDS OF CHARACTERS THAN SHARED DERIVED ONES.
Monophyletic Group:
A group containing an antecedent and all of its descendants - defined by one or more synapomorphies.

Paraphyletic Grouping:
A group consisting of an antecedent just not all of its descendants. Information technology is defined by what it does non have.
Polyphyletic Group:
A grouping that does not include a common ancestor within the group. The mutual ancestor is placed in another group.
Out Group:
A group outside the groups in question which is used to define the polarity of character transformations (primitive to derived).
Sis Group:
A monophyletic group more closely related to the group under exam than whatever other group.
Ancestor Trouble:
All possible ancestors are regarded as sister groups.

Annotation THAT THE CLADOGRAM OF THE MONOPHYLETIC GROUPS TRANSLATES Directly INTO TAXONOMIC CLASSIFICATION USING THE LINNEAN HIERARCHY.
          Phylum Chordata         Subphylum Osteichthyes                 Superclass Tetrapoda                         Infraclass Amniota                                 Class Mammalia                                         Species            Man sapiens                  
We will utilise the cladistic method in discussing the relationships of groups through the rest of the term.
Example: Homo sapiens, Crocodilus niloticus, Deinonychus antirrhopus, and Archaeopteryx lithographica
V. CLASSIFICATION
This Cladogram as well direct translates into a nomenclature

Become To Lecture half dozen

REFERENCES:
http://www.ucmp.berkeley.edu/clad/clad1.html

http://www.vims.edu/~mes/hennig/infohist/willi1.html which has as its home folio http://www.vims.edu/~mes/hennig/

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