lecture_10_3

lecture_10_3 - Galapagos tortoise: 500 lbs, ~1 meter shell...

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Unformatted text preview: Galapagos tortoise: 500 lbs, ~1 meter shell length Aldabra tortoise: 400 pounds, ~1 meter shell length Seychelles Is. A phylogeny of tortoises S m a l l- m e d i u m S m a l l- m e d i u m S m a l l- m e d i u m Large Large A phylogeny of tortoises S m a l l- m e d i u m S m a l l- m e d i u m S m a l l- m e d i u m Large Large The parsimony inference is that tortoises as a clade started out small-medium, and have essentially remained that way. Twice, we see the convergent evolution of gigantic size. Both of those are on tropical islands, suggesting that there is strong selection for large size on tropical islands. South America/Galapagos Aldabra/Madagascar The evolution of hinges in turtle shells Hinge evolves, retained in ~ 25 species Hinge evolves, retained in ~ 13 species Hinge evolves, retained in ~ 5 species Key Hinge No hinge Phylogeny of living turtles shows that: 1) Hinges evolved three times (convergence) 2) Once they have evolved, they are retained in all descendant species (stabilizing selection) Phylogenies can provide a good sense of time A B C D A B C D Cladogram Chronogram (timetree) Time Only relative branching order is depicted Branch lengths indicate absolute time To bring in time, we employ the concept of the...
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lecture_10_3 - Galapagos tortoise: 500 lbs, ~1 meter shell...

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