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Reversal Homoplasy The Case of Tetrapods

Figure 28.4 Where Do Whales Belong on the Tree of Life? (a) Data set 1 (morphological traits): Whales diverged before the origin of artiodactyls. (b) Data set 2 (DNA sequences): Whales and hippos share a common ancestor. Perissodactyls (horses and rhinos) Perissodactyls (horses and rhinos) ARTIODACTYLS Whale Camel ARTIODACTYLS Camel Peccary Gain of pulley- shaped astragalus Peccary Pig Gain of pulley-shaped astragalus Pig Hippo Hippo Whale Loss of pulley- shaped astragalus Astragalus (ankle bone) Deer Deer Figure 28.4 Where Do Whales Belong on the Tree of Life? Cow Cow (c) Data set 3 (presence and absence of SINEs): Supports the close relationship between whales and hippos. Locus 1  SINE present 0  SINE absent ?  still undetermined Cow Deer Whale Whales and hippos share four unique SINEs (4, 5, 6, and 7) Hippo Pig Peccary Camel 3

Figure 28.4b Where Do Whales Belong on the Tree of Life? Cow Deer Whale Hippo Pig Peccary Camel Loss of pulley- shaped astragalus Gain of pulley- shaped astragalus Perissodactyls (horses and rhinos) ARTIODACTYLS Figure 28.4b Figure 28.4b Where Do Whales Belong on the Tree of Life? (c) Data set 3 (presence and absence of SINEs): Supports the close relationship between whales and hippos. 1  SINE present 0  SINE absent ?  still undetermined Whales and hippos share four unique SINEs (4, 5, 6, and 7) Cow Deer Whale Hippo Pig Peccary Camel Locus 4

Vertebrate Clade Homeothermy (a homoplasy) Homeotherms are ?-phyletic http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/VertebrateClade.gif

Vertebrate Clade Homeothermy (a homoplasy) Homeotherms are polyphyletic Reptiles are? http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/VertebrateClade.gif

Reptiles are a grade (are paraphyletic) Vertebrate Clade Homeothermy (a homoplasy) Homeotherms are polyphyletic Reptiles are a grade (are paraphyletic) http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/VertebrateClade.gif

Time Distal elements and radius Ulna Humerus Tulerpeton (362 mya) Figure 25.4 Distal elements and radius Ulna Humerus Tulerpeton (362 mya) Acanthostega (365 mya) Figure 25.4 Transitional Features during the Evolution of the Tetrapod Limb. Tiktaalik (375 mya) Time Fin rays Eusthenopteron (385 mya) 8

Tetrapod Limb: Homologous Structures Figure 25.9 Tetrapod Limb: Homologous Structures Humerus Radius and ulna Carpals Metacarpals Phalanges Figure 25.9 Structural Homology: Limbs with Different Functions Have the Same Underlying Structure. Turtle Human Horse Bird Bat Seal crawl type run arm-fly hand-fly swim 9

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)

Reversal of a complex trait is comparatively 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 So 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 can be documented.

terrestrial amphibians Caecilians: terrestrial amphibians http://www.wildherps.com/images/herps/standard/017614_caecilian.jpg http://www.wildherps.com/images/herps/standard/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. unexplained-mysteries http://www.unexplained-mysteries.com/gallery/albums/userpics/22445/normal_ajolote.jpg This ajolote is a snake that reversed the reversal blocking only pectoral limbs (note: belly scale pattern and limb location) Or it is a lizard that has lost only its pelvic limbs (reversal homoplasy)

There are also partial losses: the Boa has vestigial pelvic limbs http://www.edwardtbabinski.us/images/spurs1.jpg Of course the alternative interpretation is a partial reversal of loss

This is a verified reversal of a reversal: http://www.telegraph.co.uk/earth/wildlife/6187320/Snake-with-foot-found-in-China.html This snake has reversed the reversal blocking pelvic limbs

Of course humans will make false claims! This claim of pectoral limbs is clearly false: http://robandjan.files.wordpress.com/2008/08/snake1.jpg This snake is in the act of swallowing a frog, NOT sprouting legs!

There are several clear examples of reversals of reversals but: http://dakotabirding.com/Snake_wlegs.jpg Has this snake reversed the reversal blocking pectoral limbs??

Is dark body a complex characteristic? There are two possible explanations— which is most parsimonious? OG F E B A D C dark -- body -- dark bodyR -- dark bodyR -- black eye -- long wing Two Forward Evolutions -- wide neck -- dark bodyR -- long leg -- dark body -- large eye A homoplasy of parallelism or… convergence -- thick leg -- wide body A single evolution But three reversals -- dark body F -- wide wing -- long stinger Is dark body a complex characteristic? Maybe one enzyme! Is it easier to evolve or to lose a characteristic?

Is dark body a complex characteristic? There are two possible explanations— which is most parsimonious? OG F E B A D C dark -- body -- dark bodyR -- black eye -- long wing Two Forward Evolutions -- wide neck -- dark bodyR -- long leg -- dark body -- large eye A homoplasy of parallelism or… convergence -- thick leg -- wide body A single evolution But two reversals -- dark body F -- wide wing -- long stinger Is dark body a complex characteristic? Maybe one enzyme!

And one fewer step! Maybe one enzyme! There are two possible explanations— which is most parsimonious? OG F E B A D C dark -- body -- black eye -- long wing Two Forward Evolutions -- wide neck -- long leg -- dark body -- large eye A homoplasy of parallelism or… convergence -- thick leg -- wide body F And one fewer step! -- wide wing -- long stinger Maybe one enzyme!

In other words, is the MOST PARSIMONIOUS! Make sure your homework cladogram (Page 6) is solved: applying the homoplasy to the simplest character uses the fewest steps, and uses a forward and a reverse rather than two forward evolutionary steps!! In other words, is the MOST PARSIMONIOUS!