06 - VERTEBRATE EVOLUTION - ALL

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06 - VERTEBRATE EVOLUTION - ALL Powered By Docstoc
					The Origins of Genetic Variation
• Through evolutionary time, where do all of these
  new derived traits come from?
• They can’t just appear “out of thin air.”
   – Mutations
   – Sexual Reproduction
Mutations

• Mutations, simply stated, are changes in the
  nucleotide sequence of DNA
• Mutations can cause new genes and alleles to
  arise
• Only mutations in cells that produce gametes
  can be passed to offspring
Mutations
• They can come from mistakes in copying DNA. There are
   different kinds:
  – Substitution of an incorrect letter, a DNA “typo”
  – Deletions and insertions of blocks of letters
  – Copy and Paste errors result in duplication of a single
  gene, or large blocks of genes (gene duplication)
  – Inversions, breakage and fusion of chromosomes
Genetic Variation from Sexual Reproduction
 • Example: The fusion of human gametes will produce a
   zygote with any of about 70 trillion diploid combinations!


              Key

          Maternal set of
          chromosomes
                            Possibility 1                                Possibility 2
          Paternal set of
          chromosomes

                                            Two equally probable
                                              arrangements of
                                              chromosomes at
                                                metaphase I




                                                   Metaphase II




                                                    Daughter
                                                      cells

                Combination 1      Combination 2               Combination 3   Combination 4
Genetic Variation from Sexual Reproduction
                            Prophase I                  Non sister
                                                        chromatids
 –   Crossing over          of meiosis
     produces
     recombinant                           Tetrad

     (recombined)                                        Chiasma,
     chromosomes,                                        site of
                                                         crossing
     which now will                                      over
                            Metaphase I
     carry genes
     from both
     parents
 •   Example: The
     fusion of human
     gametes will       Metaphase II
     produce a
     zygote with any
     of about 70           Daughter
     trillion diploid      cells
     combinations!
                                                Recombinant
                            Figure 13.11        chromosomes
Fig. 21-9a

        Where do new genes (new traits) come from?
                   Transposons in DNA
                                          New copy of
                   Transposon             transposon

   DNA of
   genome    Transposon
              is copied
                                                  Insertion



                Mobile transposon

     (a) Transposon movement (“copy-and-paste” mechanism)
Where do new genes (new traits) come from?
            Retrotransposons
Gene Duplications and Gene Families

• Gene duplication
  – Is one of the most important types of mutation
    in evolution, because it increases the
    number of genes in the genome, providing
    further opportunities for evolutionary changes
Does all DNA in an organism mutate
(change) at equal rates?

• DNA that codes for rRNA changes relatively slowly
  and is useful for investigating branching points
  hundreds of millions of years ago
• mtDNA and intron DNA evolves rapidly and can be
  used to explore more recent evolutionary events
Because it enlarges the genome, which source of
genetic variation below has likely resulted in the
most new traits in organisms throughout
evolutionary history?

   a) Point Mutations
   b) Gene Duplication
   c) Sexual Reproduction
   d) Crossing Over in
      Meiosis
  Reading

Chapter 32 & 34
The Family Tree of Life – 3 Domains
                     Domain Eukarya

                                   EUKARYA


                     Land plants                Dinoflagellates
            Green algae               Forams
                                          Ciliates   Diatoms
                              Red algae


                    Amoebas
Cellular slime molds
                                                           Euglena
                                                               Trypanosomes
           Animals
                                                         Leishmania
                  Fungi
• Animals are unique because they ingest food (fungus-
  digest food with enzymes on the exterior, plants make their
  own)
• They (most anyway) have muscle and nerve cells, makes
  them different; also, no cell walls
Animal Phylogeny
Kingdom Animalia
• Multicellular Eukaryotes
• Heterotrophic Metabolism: Animals are unique
  because they ingest food (fungus- digest food
  with enzymes on their exterior, plants make
  their own food)
• Cells without cell walls
• Specialized tissues for sex cell production
• First developed 575 million – 1 billion years ago
• Diploid body cells and haploid gametes
Animal Life-Cycle
  Hox gene family – Evolutionarily Important

• Hox (homeobox) genes
  are regulatory genes.
  That means they regulate
  the expression of other
  genes.
• Hox genes determine
  where limbs and other
  body segments will grow
  in animals and fungi.
• The same Hox genes
  govern the development
  of both a fruit fly and a
  human!
Hox (and other gene duplications) add derived traits
Protistan Ancestors – PreCambrian Era




        Choanoflagellate Colony
   1.2 billion – 800 million years ago
             Early Evolution of Animals
        1
                           2                      Somatic cells
                                              3                                    Digestive
                                                                                   cavity
                                                                                               5
Choanoflagellate                                                     4



                                        Reproductive cells

                     Hollow sphere
 Colonial protist,   of unspecialized   Beginning of cell         Infolding,          Gastrula-like
 A solid colony of   cells (shown in    specialization            (Gastrulation)      “protoanimal”
 identical cells     cross section)




  Animals begin as a solid colony of identical cells,
  Evolve into larger infolded layers of Specialized Cells
Animals - Bilateral vs. Radial Symmetry

                               Radial – Attached or
                               drifting organisms,
                               their symmetry equips
                               them to meet their
                               environment equally
                               well from all sides

                               Bilateral – Actively
                               move from place to
                               place, with a central
                               nervous system to
                               coordinate crawling,
                               burrowing, flying,
                               swimming.
Animal Phylogeny – Radial / Bilateral Split
Most bilaterates have a complete gut.
Fig. 32-2-3


   Animal Embryology (Development from Zygote)



                                                                                         Blastocoel
                                                                                         Endoderm
              Cleavage          Cleavage Blastula

                                                                                          Ectoderm


    Zygote         Eight-cell stage                       Gastrulation        Gastrula
                                                    Blastocoel      Blastopore-
                                       Cross section                The beginnings
                                        of blastula                 of a Gut
Fig. 32-8a


        Gastrulation results in a “Tube within a Tube”
         body plan: a Coelom (think mouth to anus)
                          Coelom
                                        Body covering
                                        (from ectoderm)


                                        Tissue layer
                                        lining coelom
                  Digestive tract       and suspending
                  (from endoderm)       internal organs
                                        (from mesoderm)

   (a) Coelomate
Animal Phylogeny: Protostome and Deuterostome Split
Fig. 32-9
                  Protostome development      Deuterostome development
                    (examples: molluscs,       (examples: echinoderm,
                         annelids)                   chordates)
                                                                           (a) Cleavage (division)
                      Eight-cell stage                Eight-cell stage




                   Spiral, determinate         Radial, indeterminate
 Key                                                                       (b) Coelom formation
                                              Coelom
       Ectoderm
       Mesoderm
       Endoderm
                                                                         Deuterostomes
                                    Coelom
                                                                         develop
                                Blastopore     Blastopore                “Butt-first”!

                                                                           (c) Fate of the blastopore
                                Anus                           Mouth


                                     Digestive tube


                                Mouth                       Anus
            Mouth develops from blastopore.      Anus develops from blastopore.
What is the evolutionary significance of
gastrulation, which formed blastopores in early
organisms?
  a) It made it easier for
     organisms to exchange
     gases like oxygen
  b) It gave them radial
     symmetry
  c) It gave them a digestive
     tract
  d) It gave them bilateral
     symmetric
Protostome Invertebrates
  Invertebrates

• Animals without
  Backbones
• Majority of
  animal kingdom
• Includes
  approximately
  32 phyla
Deuterostomia
Chordates – All Share These Traits
• Notochord
  (vertebral discs)

• Dorsal hollow
  nerve cord
  (brain and spinal
  cord)

• Phyaryngeal
  (gill) slits or
  gill pouches
  (parts of ear, head
  and neck)

• Post anal tail
  (skeletal elements
  and muscles)
Giant
luminescent
salps-
Pyrosoma
The adult turnicate lacks many
chordate characteristics
               Incurrent
               siphon
               to mouth

               Excurrent
               siphon



                                    Excurrent
                Atrium
                                    siphon

                Pharynx
                 with
               numerous
                 slits              Anus
                                   Intestine
                Tunic
                                  Esophagus
                                 Stomach
                                               Chordates
                                                     Craniates
                                                           Vertebrates
                                                                  Gnathostomes
                                                                       Osteichthyans
                                                                                 Lobe-fins
                                                                                         Tetrapods
                                                                                               Amniotes




                                                                                                              Milk


                                                                                                        Amniotic egg


                                                                                                 Legs




                                                                              Lobed fins


                                                                     Lungs or lung derivatives


                                                         Jaws, mineralized skeleton


                                                  Vertebral column


                                        Head


                                Brain


                         Notochord



Ancestral deuterostome
Craniates are chordates that have a head
• The origin of a head
  opened up a completely
  new way of feeding for
  chordates: active
  predation
• All Craniates share
  some characteristics:
   – a skull
                               Hag fish (Class Myxini)
   – a brain               •   Most primitive craniate (it’s got a head!)
                           •   Skull made of cartilage (not bone)
   – eyes, and other
                           •   No jaws or vertebrae
     sensory organs
                           •   Hagfish makes lots of SLIME (several
• Are we craniates?            liters(!) in <1 minute)
                           •   http://www.youtube.com/watch?v=Bb2EOP3ohnE
Derived Characters of Craniates – Hox Genes!
• Craniates have two clusters of Hox genes; lancelets and
  tunicates(no heads) have only one cluster
• One feature unique to craniates is the neural crest, a
  collection of cells in an embryo which give rise to a variety
  of structures in later crainiates, including some of the
  bones and cartilage of the skull

Dorsal edges      Neural   Neural
of neural plate   crest    tube




                                Migrating neural
            Notochord           crest cells
On to Vertebrates: They’re Craniates with a
Backbone (first ones were made of cartilidge)
Derived Characters of Vertebrates

• During the Cambrian period, a lineage of craniates evolved
  into vertebrates
• Vertebrates underwent further gene duplication, resulting in
  more complexity                    1 cm


• Vertebrates derived characters:
   –   Vertebrae enclosing a spinal cord
   –   An elaborate skull
   –   Mineralized mouthparts

Vertebrates became more efficient
at capturing food and avoiding
being eaten
                                           Conodonts had mineralized mouthparts
Lampreys are the oldest living linage of
            vertebrates
 Gnathostomes are vertebrates that have jaws




• The earliest gnathostomes in the fossil record are an extinct
  lineage of HUGE armored vertebrates like this one!
Origins of Bone and Teeth

• Mineralization (bone vs. cartilidge) appears to
  have originated with vertebrate mouthparts (jaws)
• But… the vertebrate skeleton became fully
  mineralized after these guys….
Derived Characters of Gnathostomes
• Gnathostomes have jaws that might have evolved from
  skeletal supports of the pharyngeal slits
    Gill slits   Cranium




                      Mouth
           Skeletal rods

•      Additional duplication of Hox genes (4) and other gene
       clusters, allowing for… you guessed it… Increased
       complexity!
•      An enlarged forebrain associated with enhanced smell
       and vision
•      In aquatic gnathostomes, there is the lateral line system,
       which is sensitive to vibrations
Hox (and other gene duplications) add derived traits
    Other Gnathostome Taxa
• Chondrichthyans (Sharks,
  Rays, and their relatives)-
  another group of jawed
  vertebrates; skeleton
  composed primarily of cartilage
•    Shark eggs are all fertilized internally, but
     embryos can develop in different ways:
      –    Oviparous: young hatch from eggs
           laid outside the mother’s body
      –    Ovoviviparous: young hatch from
           eggs that are retained in the
           mother’s uterus
      –    Viviparous: young are born alive
           after having been nourished in the
           uterus by blood from the placenta
More Gnathostomes:
Osteichthyes, Ray-Finned
Fishes and Lobe-Fins
• The vast majority of
  vertebrates belong to a
  group of gnathostomes
  called Osteichthyes
• Osteichthyes includes
  the bony fish, and
  tetrapods
Lobe-Fins: Transition to Amphibians, and to Land!
• The lobe-fins (Sarcopterygii) have muscular pelvic and
  pectoral fins
• Three lineages survive and include coelacanths, lungfishes,
  and tetrapods
Tetrapods: Gnathostomes that have limbs

• One of the most significant events in vertebrate
  history was when the fins of some lobe-fins
  evolved into the limbs and feet of tetrapods

Derived Characters of Tetrapods
• Tetrapods have some specific adaptations:
  – Four limbs
  – Feet with digits
  – Ears for detecting airborne sounds
The Origin of Tetrapods
• In one lineage of
  lobe-fins, the fins
  became
  progressively more
  limb-like while the
  rest of the body
  retained
  adaptations for
  aquatic life
• For example,
  Acanthostega lived
  in Greenland 365
  million years ago
Amphibians
• Amphibian means “both ways of life,” refers to
  the metamorphosis of an aquatic larva into a
  terrestrial adult
• Most amphibians
  have moist skin that
  complements the
  lungs in gas
  exchange
• Fertilization is
  external in most
  species, and the eggs
  require a moist
  environment
  Aquatic larvae (tadpole), terrestrial adult (frog)




(a) Tadpole



              (b) During
                  metamorphosis   (c) Mating adults
(salamanders)




     (frogs)




(legless, rare)
One “moist environment” for amphibian eggs!
Amniotes are tetrapods that have a terrestrially
adapted egg

• Amniotes are a group of tetrapods whose
  living members are the reptiles, including birds,
  and mammals
• Amniotes have other terrestrial adaptations
  – relatively impermeable skin
  – ability to use the rib cage to ventilate the
    lungs
Derived Characters of Amniotes
• Amniotes are named for the major derived character of the
  clade, the amniotic egg, which contains membranes that
  protect the embryo




• The amniotic egg was a key innovation for terrestrial life: it
  allowed the embryo to develop on land, in its own “private pond.”,
• No more dependence upon a water environment for reproduction!
Reptiles
• The reptile clade includes the tuataras, lizards,
  snakes, turtles, crocodilians, birds, and the
  extinct dinosaurs

• Reptiles have scales
  that create a
  waterproof barrier
• They lay shelled
  eggs on land
                        Male green iguana


Most reptiles are ectothermic, absorbing
external heat as the main source of body
heat. Birds, however, are endothermic.
Turtles
• Turtles are the most distinctive group of reptiles alive today
• All turtles have a boxlike shell made of upper and lower
  shields that are fused to the vertebrae, clavicles, and ribs
• Some turtles have adapted to deserts and others live
  entirely in ponds and rivers




(d) Eastern box turtle (Terrapene
    carolina carolina)
The Origin of Birds
• Birds probably
  descended from small
  theropods, a group of
  carnivorous dinosaurs
• By 150 million years
  ago, feathered
  theropods had evolved
  into birds

Derived Characters of Birds
• The major adaptation is wings with keratin feathers
• Other adaptations include lack of a urinary bladder,
  females with only one ovary, small gonads, and loss of
  teeth
Mammals are amniotes that have hair and milk
 • By the early Cretaceous (65 mya), the three
   living lineages of mammals emerged:
   monotremes, marsupials, and eutherians
 • Derived Characters
   – Mammary glands, which produce milk
   – Hair
   – A larger brain than other vertebrates of
     equivalent size
   – Differentiated teeth
Monotremes
• Monotremes are a small group of egg-laying
  mammals (echidnas and platypus)
Marsupials
• Marsupials include
  opossums, kangaroos, and
  koalas
• The embryo develops
  within a placenta in the
  mother’s uterus
• A marsupial is born very
  early in its development
• It completes its embryonic
  development while nursing
  in a maternal pouch called
  a marsupium
   Primates
• Most primates have
  hands and feet
  adapted for grasping
• Other derived
  characters of
  primates:

– A large brain and short jaws
– Forward-looking eyes close together on the face,
  providing depth perception
– Complex social behavior and parental care
– A fully opposable thumb (in monkeys and apes)
  Primates - Monkeys
• The first monkeys evolved in
  the Old World (Africa and
  Asia)
• In the New World (South
  America), monkeys first
  appeared roughly 25 million
  years ago
• New World and Old World
  monkeys underwent separate
  adaptive radiations during
  their many millions of years of
  separation
  Primates - Apes
• The other group of anthropoids consists of primates
  informally called apes
• This group includes gibbons, orangutans, gorillas,
  chimpanzees, bonobos, and humans
• Apes diverged
  from Old World
  monkeys about
  20–25 million
  years ago
Primates - Hominins

• The study of human origins is known as
  paleoanthropology
• Hominins (formerly called hominids) are more
  closely related to humans than to chimpanzees
• Paleoanthropologists have discovered fossils
  of about 20 species of extinct hominins
• Hominins originated in Africa about 6–7 million
  years ago
• Early hominins had a small brain but probably
  walked upright
  The Genetic Connection

• Rapid expansion of our species may have
  been preceded by changes to the brain that
  made cognitive innovations possible
  – For example, the FOXP2 gene is essential for
    human language, and underwent intense
    natural selection during the last 200,000 years

• Homo sapiens were the first group to show
  evidence of symbolic and sophisticated thought

				
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