INTRODUCTION TO ANIMAL DIVERSITY

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INTRODUCTION TO ANIMAL DIVERSITY

• Chapter 32
• Our Kingdom
• We are Animals

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Animals Are

• Species-rich
• Morphologically diverse lineage of multicellular
  organisms on the tree of life
• Distinguished by two traits
• they eat
• they move
• The largest and most abundant predators,
  herbivores, and detritivores

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Animals Are

• Multicellular, heterotrophic eukaryotes
• Heterotrophs
• ingest food
• find food by tunneling, swimming, filtering,
  crawling, creeping, slithering, walking, running,
  or flying.
• Dominant consumers in both aquatic and
  terrestrial habitats
• Animal cells lack cell walls
• Distinguished by two tissues
• Nervous tissue and muscle tissue
• Most animals reproduce sexually with the diploid
  stage usually dominating the life cycle

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Methods in the Study of Animals

• Analyzing Comparative Morphology
• The Evolution of Tissues
• Symmetry and Cephalization
• Evolution of a Body Cavity
• The Protostome and Deuterostome Patterns of
  Development
• The Tube-within-a-Tube Design
• A Phylogeny of Animals Based on Morphology
• Using the Fossil Record
• Evaluating Molecular Phylogenies

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Themes in the Diversification of Animals

• Suspension (Filter) Feeding
• Deposit Feeding
• Herbivory
• Predation
• Parasitism
• FeedingMovement
• Types of Limbs Unjointed and Jointed
• Are All Animal Appendages Homologous?
• Reproduction and Life Cycles

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Key Lineages of Animals

• Choanoflagellates (Collar Flagellates)
• Porifera (Sponges)
• Cnidaria (Jellyfish, Corals, Anemones, Hydroids,
  Sea Fans)
• Ctenophora (Comb Jellies)
• Acoelomorpha

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Monophyletic and Very Diverse

• The animals are a monophyletic group
• Animals are very diverse
• 34 major animal phyla are recognized

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Analyzing Comparative Morphology

• Most morphological diversity in animals is based
  on
• differences in mouths and limbs

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Basic Architecture

• Four features define an animal's body plan
• the number of tissue types in embryos
• the type of body symmetry
• the presence or absence of a fluid-filled cavity
• the way in which the earliest events of embryo
  development proceed

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The Evolution of Tissues

• All animals other than sponges have tissues
• tightly integrated structural and functional
  units of cells.
• Diploblasts
• embryos have two types of tissues or germ layers
• Ectoderm
• Endoderm
• Triploblasts
• embryos have three types of tissues
• Ectoderm
• Endoderm
• Mesoderm
• germ layers develop into distinct adult tissues

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Symmetry and Cephalization

• A basic feature of a multicellular body is the
  presence or absence of a plane of symmetry
• radial symmetry
• at least two planes of symmetry.
• bilateral symmetry
• a single plane of symmetry
• face their environment in one direction.

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Cephalization

• Bilateral symmetry allowed
• Evolution of a head, or anterior region, where
  structures for feeding, sensing the environment,
  and processing information are concentrated

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Evolution of a Body Cavity

• Animals may or may not have an internal,
  fluid-filled body cavity
• coelom
• forms from within the mesoderm
• lined with cells from the mesoderm

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Advantages of a Coelom

• Creates a medium for circulation
• Makes space for internal organs
• A hydrostatic skeleton
• fluid-filled chamber
• allows movement
• even without fins or limbs.

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The Protostome and Deuterostome Patterns of
Development

• Coelomates are bilaterally symmetric
• except echinoderms
• three embryonic tissue layers
• Bilatera
• protostomes
• arthropods, mollusks, and segmented worms
• deuterostomes
• vertebrates and echinoderms

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Differences in Early Development

• Three events in early development differ in
  protostomes and deuterostomes
• Cleavage
• Gastrulation
• coelom formation

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Cleavage

• Rapid series of mitotic divisions
• Spiral cleavage
• mitotic spindles of dividing cells orient at an
  angle to the main axis of the cells
• resulting in a helical arrangement
• Radial cleavage
• mitotic spindles of dividing cells orient
  parallel or perpendicular to the main axis of the
  cells
• resulting in a pattern of cells stacked directly
  on top of each other

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The Tube-within-a-Tube Design

• The basic animal body plan is a
  tube-within-a-tube design in which the outer tube
  forms the body wall and the inner tube forms the
  gut

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Ancestor?

• The animal kingdom all developed from a common
  ancestor ( monophyletic) probable during the
  Precambrian era.
• 
  
  
• Probably a colonial choanoflagelate that lived
  about700 million years ago. Modern
  choanoflagellates are tiny, have a stalk and live
  in ponds and lakes)
• A hypothesis of animal origin from flagellated
  protists says that the colony of cells in the
  protist evolved into a sphere and then
  differenciated and especialized creating two
  layers of cells.

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The common ancestor of living animals

• May have lived 1.2 billion800 million years ago
• May have resembled modern choanoflagellates,
  protists that are the closest living relatives of
  animals

Figure 32.3
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closest living relatives of animals

• a colonial, flagellated protist

Figure 32.4
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A Phylogeny of Animals Based on Morphology

• The phylogenetic tree indicates that a group of
  protists called the choanoflagellates are the
  closest living relatives of animals and that the
  Porifera (sponges) are the most ancient animal
  phylum.

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Phylogeny Based on Morphology
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• Radially symmetric phyla are placed on the tree
  next because their tubelike body plans are
  relatively simple. Among the bilaterally
  symmetric phyla, the acoelomates and
  pseudocoelomates appeared first, followed by the
  coelomates.

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• Two major events occurred after the coelomates
  split into the protostomes and deuterostomes
• radial symmetry evolved
• segmentation evolved independently in both
  lineages of coelomates.

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Using the Fossil Record

• Most major groups of animals appear in the
  fossil record starting about 580 million years
  ago
• The fossil record is generally consistent with
  the morphological phylogeny.

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Neoproterozoic Era (1 Billion524 Million Years
Ago)

• Early members of the animal fossil record are
  known as the Ediacaran fauna( first fossils of
  animals about 575 mya). Simple radial forms and
  segmented bodies with legs.

Figure 32.5a, b
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Paleozoic Era (542251 Million Years Ago)

• The Cambrian explosion marks the earliest fossil
  appearance of many major groups of living animals
• Is described by several current hypotheses such
  as predator- prey relationships, oxygen increase
  and evolution of the hox genes

Figure 32.6
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Mesozoic Era (25165.5 Million Years Ago)

• During the Mesozoic era
• Dinosaurs were the dominant terrestrial
  vertebrates
• Coral reefs emerged, becoming important marine
  ecological niches for other organisms
• The first mammals appeared (tiny, nocturnal
  insect eaters

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Cenozoic Era (65.5 Million Years Ago to the
Present)

• The beginning of this era
• Followed mass extinctions of both terrestrial and
  marine animals
• Modern mammal orders and insects
• diversified during the Cenozoic
• Also flowering plants appeared

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Evaluating Molecular Phylogenies

• The phylogenetic tree based on genes for
  ribosomal RNA and several proteins

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Points of Agreement

• All animals share a common ancestor
• Sponges are basal animals (branch from the base
  of tree, no tissues)
• Eumetazoa is a clade of animals with true tissues
• Most animal phyla belong to the clade Bilateria
• Vertebrates belong to the clade Deuterostomia

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Disagreement over the Bilaterians

• The morphology-based tree
• Divides the bilaterians into two clades
  deuterostomes and protostomes
• In contrast, recent molecular studies
• assign two sister taxa to the protostomes rather
  than one the ecdysozoans and the lophotrochozoans

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Important Observations Emerge From the Data

• The most ancient triploblasts lacked a coelom
• The major event in the evolution of the Bilateria
  was the split between protostomes and
  deuterostomes
• Segmentation evolved independently in the
  annelids and the arthropods and
• Pseudocoeloms arose from coeloms twice in
  evolutionary history

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Phylogenetic trees are best described as

• true and inerrant statements about evolutionary
  relationships.
• hypothetical portrayals of evolutionary
  relationships.
• the most accurate possible representations of
  genetic relationships among taxa.
• theories of evolution.
• the closest things to absolute certainty that
  modern systematists can produce.

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Themes in the Diversification of Animals

• Within the phylum
• basic features of the body plan do not vary from
  species to species
• Diversity arose
• mostly because of the evolution of innovative
  methods for feeding and moving

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Feeding

• The feeding tactics observed in animals can be
  broken into five general types
• suspension feeding
• deposit feeding
• herbivory
• predation
• Parasitism
• Many animals undergo a metamorphosis
• a change in form during development
• allows juveniles and adults to exploit different
  sources of food

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Suspension (Filter) Feeding

• Suspension feeders, or filter feeders, capture
  food by filtering out particles suspended in
  water or air
• This method is found in a wide variety of animal
  groups and has evolved many times independently

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Deposit Feeding

• Deposit feeders eat their way through a
  substrate
• Food
• soil-dwelling bacteria, protists, fungi, and
  archaea
• detritusthe dead and partially decomposed
  remains of organisms
• Depending on food
• herbivores (plant eaters), parasites,
  detritivores (detritus eaters), or predators

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Herbivory

• Herbivores
• animals that digest algae or plant tissues
• complex mouths with structures that make biting
  and chewing or sucking possible

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Predation

• Sit-and-wait predators rarely move at all until
  prey is captured
• stalkers pursue their prey

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Parasitism

• Parasites are much smaller than their victims
  and often harvest nutrients without causing death
• Endoparasites
• live inside their hosts
• often wormlike in shape
• can be extremely simple morphologically
• Ectoparasites
• live outside their hosts
• usually have grasping mouthparts
• pierce the hosts exterior and suck the
  nutrient-rich fluids inside

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Movement

• Many animals are sit-and-wait predators, and
  some are sessile throughout their adult lives.
  But the vast majority of animals move under their
  own power either as juveniles or as adults.

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Function of Movement

• three functions in adult animals
• Finding food
• finding mates
• escaping from predators.

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Limbs

• A major innovation in animals
• made highly controlled, rapid movement possible
• Two types
• Unjointed
• saclike
• Jointed
• move when muscles that are attached to a skeleton
  contract or relax

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Homologous vs Non-Homologous

• Biologists have argued that at least a few of
  the same genes are involved in the development of
  all appendages observed in animals
• Hypothesis is that all animal appendages have
  some degree of genetic homology
• that they are all derived from appendages that
  were present in a common ancestor.
• This hypothesis is controversial, however, and
  research continues

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Reproduction and Life Cycles

• At least some species in most animal phyla can
  reproduce asexually (via mitosis), as well as
  sexually (via meiosis).
• Sexual reproduction can occur with internal or
  external fertilization

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Development

• Eggs or embryos may be retained in the females
  body during development
• viviparous
• May be laid outside the body
• oviparous
• Female retains eggs inside her body during early
  development
• embryos are nourished by yolk inside the egg and
  not by nutrients transferred directly from the
  mother
• ovoviviparous
• Vast majority of animals are oviparous

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Development

• After a sperm fertilizes an egg
• The zygote undergoes cleavage, leading to the
  formation of a blastula
• The blastula undergoes gastrulation
• Resulting in the formation of embryonic tissue
  layers and a gastrula

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• Early embryonic development in animals

Figure 32.2
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Metamorphosis

• The change from juvenile to adult body type
• Larva
• juvenile individual
• looks substantially different from the adult
• Nymph
• juvenile individual
• looks like a miniature adult

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Pupation

• When a larva has grown sufficiently, it secretes
  a protective case and is now known as a pupa

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Into an Adult

• During pupation, the pupas body is completely
  remodeled into a new, adult form

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Holometabolous

• Complete metamorphosis
• two-step process
• from larva to pupa to adult
• involving dramatic changes in morphology and
  habitat use

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Hemimetabolou

• Incomplete metamorphosis
• One-step process of sexual maturation.
• Limited morphological difference between juvenile
  and adult

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Marine Animals

• Complete metamorphosis
• extremely common in marine animals
• most cnidarians have two distinct body types
  during their life cycle
• a largely sessile form called a polyp
• alternates with a free-floating stage called a
  medusa

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