Transcript Reversal Homoplasy

The diagram you produced on Page 4 of Cladistics:
OG
E
B
A
-- long wing
-- large eye
The
differences in
the in-group
are explained
in 10 steps!
D
C
-- black eye
-- wide neck
-- long leg
-- dark body
-- thick leg
-- wide body
Comma
-- wide wing separation at
-- long stinger one step might
be clearer!
Your cladogram uses numbered traits…
I am doing it this way for a reason…
This diagram is based on the same clade critter data…
But is not the result of cladistic analysis:
OG
E
B
A
D
C
25 Steps!!
<-- black eye
<-- long leg
<-- dark body
<-- wide neck
<-- thick leg
<-- wide body
<-- long wing
<-- large eye
<-- wide wing
<-- long stinger
What concept was used to make this diagram?
Scientists reject this diagram because of parsimony…why?
This is likely your cladogram from Page 4 of Cladistics
OG
E
B
-- long wing
-- large eye
A
D
C
-- black eye
-- wide neck
-- long leg
-- dark body
-- thick leg
-- wide body
-- wide wing
-- long stinger
What do we do with the newly-discovered Clade Critter (page 5)?
OG
E
B
-- long wing
-- large eye
A
D
C
-- black eye
-- wide neck
-- long leg
-- dark body
-- thick leg
-- wide body
-- wide wing
-- long stinger
F
There are two possible explanations—
which is most parsimonious?
OG
F
E B
A
D
C
-- dark R
dark --- black eye
body
-- long wing
body
Two
-- wide neck
R
-- dark body
-- long leg
Forward
-- dark body
Evolutions
-- large eye
A homoplasy of
-- thick leg
parallelism or…
-- wide body
convergence
A single evolution
But two reversals
-- dark body
-- wide wing
-- long stinger
F
Is it easier to evolve or to lose a characteristic?
Reversal Homoplasy
The Case of Tetrapods
Vertebrate Clade
Homeothermy
(a homoplasy)
Homeotherms
are polyphyletic
Reptiles are?
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/VertebrateClade.gif
Adopted Text:
Freeman Biological Science
Pearson
Figure 25.4
Tulerpeton (362 mya)
Acanthostega (365 mya)
Tiktaalik (375 mya)
Time
Fin rays
Eusthenopteron (385 mya)
Adopted Text:
Freeman Biological Science
Pearson
Figure 25.9
Tetrapod Limb: Homologous Structures
Humerus
Radius
and ulna
Carpals
Metacarpals
Phalanges
Turtle
Human
Horse
Bird
crawl
type
run
arm-fly
Bat
hand-fly
Seal
swim
Tetrapod limbs are complex
Ball joint at girdle (pectoral or pelvic)
Proximal segment has one heavy bone
Hinge joint at elbow or knee
Distal segment has two bones for rotation
of hand/foot
Small cuboidal bones at wrist and ankle for
flexibility of hand/foot position
Long metacarpal/metatarsals for
palm/instep
Phalanges for the digits (fingers/toes)
Tetrapod limbs are stereotypical
The complex structures are shared among these
tetrapods:
Amphibians
Reptiles
Birds
Mammals
Conclusion: rather than evolving complex limb form
and function separately and identically among all
these groups of species (i.e., many homoplasies),
the tetrapod leg design evolved just once in a
common ancestor (i.e., more parsimonious)
Forward evolution of a leg requires modification of:
• Bones
• Muscles
• Connectives
• Vascular Paths
• Neural Paths
Reversal of a complex trait is comparatively parsimonious
Reversal could be just ONE point mutation in ONE gene
that normally puts limb development into motion.
Without the first step, the rest does not happen.
Tetrapod evolution has been reversed multiple times!
Thus, it must be easily done… i.e. is parsimonious
Legless amphibians: caecilians
Legless lizards: glass lizards
Ajolote: mole lizards
Snakes
Some gene functioning early in tetrapod development can
mutate (become defective), rendering some ancestral
species (and its descendants) legless.
All the rest of the tetrapod genes that had evolved to
make the limbs, are made useless by this one mutation.
The useless genes are still present, however! And this
can be evidenced and documented.
Caecilians:
Tetrapod leg reversed
in
terrestrial amphibians
http://www.wildherps.com/images/herps/stand
ard/017614_caecilian.jpg
http://www.wildherps.com/images/herps/stand
ard/017612_caecilian.jpg
http://scienceblogs.com/zooillogix/caecilian.bmp
A photo of parent Caecilian with offspring
R635RmqosDI/AAAAAAAANYc/jwcNDv1suD4/flesh+eating+amphibian+caecilians%5B2%5D
http://www.unexplainedmysteries.com/gallery/albums/userpics/22445/normal_ajolote.jpg
This ajolote is a snake that reversed the reversal restoring
pectoral limbs (note: belly scale pattern and limb location)
http://www.edwardtbabinski.us/images/spurs1.jpg
There are also partial losses: the Boa has vestigial pelvic limbs
Of course the alternative interpretation is a partial reversal of loss
http://dakotabirding.com/Snake_wlegs.jpg
There are several clear examples of reversals of reversals:
This snake has reversed the reversal, restoring pectoral limbs
http://www.telegraph.co.uk/earth/wildlife/6187320/Snake-with-foot-found-in-China.html
This is another verified reversal of a reversal:
This snake has reversed the reversal, restoring a pelvic limb
Of course humans will make false claims!
http://robandjan.files.wordpress.com/2008/08/snake1.jpg
This claim of pectoral limbs is clearly false:
This snake is in the act of swallowing a frog, NOT sprouting legs!
There are two possible explanations—
which is most parsimonious?
OG
F
E B
A
D
C
-- dark R
dark --- black eye
body
-- long wing
body
Two
-- wide neck
R
-- dark body
-- long leg
Forward
-- dark body
Evolutions
-- large eye
A homoplasy of
-- thick leg
parallelism or…
-- wide body
convergence
A single evolution
But two reversals
-- dark body
-- wide wing
-- long stinger
Is dark body a
complex
characteristic? Maybe one enzyme!
F
There are two possible explanations—
which is most parsimonious?
OG
F
E B
A
D
C
Two
Forward
Evolutions
dark -body
A homoplasy of
parallelism or…
convergence
And one
fewer
step!
-- long wing
-- large eye
-- black eye
-- wide neck
-- long leg
-- dark body
-- thick leg
-- wide body
-- wide wing
-- long stinger
Maybe one enzyme!
F
Make sure your homework cladogram
(Page 6) is solved:
1. applying the homoplasy to the simplest character
2. uses the fewest steps, and
3. uses a forward and a reverse rather than two
forward evolutionary steps!!
In other words, is the
MOST PARSIMONIOUS!