Transcript Kingdom Animalia - College of the Atlantic

The Origins of Life on
Earth
(or, a History of our planet
in a week or less)
Biology 2, College of the Atlantic
Spring 2002
• How old is this planet anyway?
• Theories of Origin
• Geological and Biological
timescales
• Phylogeny (and an awful lot of it)
How old is this planet anyway?
• The Universe is probably ~13 billion
years old (Big Bang Theory/Doppler
Shift)
• Earth is ~4.5 billion years old (begins
with cooling of crust/solidification)
• Earliest records of life ~3.5 billion years
ago
• First humans (Australopithecus), 0.005
billion years ago
• Discovery of Australopithecus fossils ,
The Fragility of Life - Coincidence
#1
• Life can only exist
within temperatures
corresponding to the
boiling and freezing
point of water
• This range is a
fraction of the range
between absolute
zero (-273°C) and
the temperature of
the sun (106°C)
How did life evolve?
• Three theories
– Creationism
– Extraterrestrial origin (Panspermia)
– Spontaneous Origin (Coincidence #2)
Physical conditions of early
Earth - Coincidence #3
• Temperatures in correct range (in
general, water in fluid state, carbon
compounds non-brittle)
• Size of planet retains an atmosphere
• Early atmosphere lacked oxygen,
therefore highly reductive
• High energy bombardment from sun
promotes generation of organics
Spontaneous origins of life - 4
steps
• Abiotic synthesis and accumulation of
organic compounds
• Polymerization
• Aggregation of polymers into nonliving
structures (Protobionts)
• Origin of heredity
Experimental evidence of
Spontaneous Origin
• Theories of Oparin and Haldane—tested by
Miller and Urey—demonstrate formation of
organics under conditions typical of early
Earth
• Polymerization can occur with appropriate
substrate
• Abiotically produced proteins (proteinoids)
self-assemble into Protobionts (selectively
permeable membrane)
The final key - Heredity
• First passage of genetic information
probably occurred through short strands
of RNA (also autocatalyst, e.g
ribozymes)
• Mutations cause variation
• “Natural selection” of molecular
combinations
• Origin of DNA
Biological time scales
• Biological timescales by necessity follow
geological timescales
• Often, geological events marked by key
biological events (mass
extinctions/diversifications)
• First fossil record of life 3.5 billion years
ago (prokaryote), in the Precambrian
• Earliest eukaryote ~1.5 billion years ago
(endosymbiotic theory)
Earth - The Early Years
• Late Precambrian saw the first
eukaryotic multicellular life
• Boundary between Precambrian and
Cambrian (580 mya) marked by a rapid
adaptive radiation/diversification of
marine life (Cambrian explosion)
• By the middle of the Cambrian, all of the
animal phyla existing today had evolved
The drive behind MacroEvolution
• Biological forces: natural selection
working in general, but particularly
effectively on genes controlling
– allometric growth
– paedomorphosis
• Physical forces
– Plate tectonics, leading to formation and
splitting of supercontinents
The study of evolutionary
history: Phylogeny
• Modern Darwinian synthesis suggests
adaptive radiation from a common ancestor
• Concept of phylogeny supported through
studies of homology
• Traditional classification systems (Linnaeus)
are monophyletic, based on homology 
parallel or divergent evolution
• Some groupings are polyphyletic, with
analogous structure  convergent evolution
The Kingdom System
• Scientists follow various taxonomic
systems: Campbell uses the 5 kingdom
classification scheme
– Monera
– Protista
– Plantae
– Fungi
– Animalia
Phylogeny recounts the
“natural selection” of species
(Earth: the Middle Years)
• First major extinction at end of the Paleozoic era
(the Permian Extinction), probably caused by
collision of tectonic plates to form the
supercontinent, Pangaea
• Pangaea marks the birth of a new era, the
Mesozoic (Triassic, Jurassic, Cretaceous)
• Mesozoic ends with second mass extinction—
the Cretaceous Extinction (impact hypothesis)
And now...
• Currently in the Recent epoch of the
Quarternary period of the Cenozoic era
• History may tell of a third mass
extinction?
• Radically changing planet will continue
to apply selective pressure to species
Monera :
the Pioneers of Life on Earth
• The most ‘successful’ group of
organisms on the planet
• 3.5 billion year history
• Although only 4000 species known, the
number of extant species is thought to
be ~4,000 – 4 x106
• Found in all ecological niches, including
some where other forms of life cannot
exist
The current importance of
Monera
• In some cases at base of food chain
• Vital roles in various elemental cycles
– Carbon cycle
– Nitrogen cycle
• Interactions with human life
– Symbiosis (E.coli)
– Pathogenic bacteria (physical,
exo/endotoxins)
– Commercial/Industrial/Scientific uses
The phylogeny of Prokaryotes
Early Prokaryote
Domain
Bacteria
(Eubacteria)
Domain
Archaea
(Archaebacteria)
Protista
Domain
Eukarya
(Eukaryotes)
Fungi
Plantae
Animalia
Archaebacteria
• Treated either as Domain, or subphylum
• Cell plan similar to most primitive
prokaryotic fossils
• Tend to exist in extreme environments
• Smaller group of species
– Methanogens (mmm-mmmm!)
– Extreme Halophiles
– Extreme Thermophiles (Sulfolobus)
Eubacteria
• More diverse group
– Spirochetes (Treponema)
– Clamydias (Clamydia trachomatis)
– Gram-positive eubacteria (Bacillus)
– Cyanobacteria (blue-green alga)
– Proteobacteria (E.coli, Salmonella)
Structure
• Small (1-5 µm)
• Of three general shapes
– Coccus (pl. cocci), e.g. Streptococcus
– Bacillus (pl. bacilli) e.g. Bacillus
– Spirillum (pl. spirilla) e.g. Treponema
• Cell wall made of peptidoglycan
– Leads to gram +/-ve distinction
• Some have a capsule, and/or pili,
and/or flagella
Physiology
• Various forms of nutrition
– Autotrophs (obtain carbon from inorganic
CO2
• Photoautotrophs (energy from sunlight)
• Chemoautotrophs (energy from inorganics)
– Heterotrophs (carbon from organics)
• Photoheterotrophs
• Chemoheterotrophs**
• Origins of glycolysis, chemiosmosis and
cellular respiration
Reproduction
•
•
•
•
Single strand of DNA
No mitosis/meiosis
Only Binary fission
Some sexual recombination through
– Transformation
– Conjugation
– Transduction
• Some form endospores
Kingdom Animalia
Invertebrata
•
•
•
•
What is an animal?
Anatomy, Embryology and Ontogeny
Parazoa
Eumetazoa
– Radiata/Bilateria
– Acoelomate/Pseudocoelomate/Eucoelomate
– Protostomes/Deuterostomes
What is an animal?
• Likely ancestor is a protist: a Precambrian
choanoflagellate
• Multicellular, heterotrophic eukaryotes
(usually exhibit ingestion)
• Storage of energy-rich reserves as glycogen
• Lack of cell walls. Unique cell junctions
• Unique tissues: muscle, nervous tissue
• Unique embryology
Embryology
• Diploid zygote divides by the mitotic
process of cleavage
• Formation of blastula followed by
gastrulation (creation of gastrula)
• Mode of embryological development
provides a taxonomic key to invertebrates
First taxonomic dichotomy
• Asymmetry versus Symmetry divides
Kingdom Animalia into sub-kingdoms:
– Parazoa (lacks tissues, asymmetrical, “like
animals”). Represented by only one
phylum: Porifera (sponges)
– Eumetazoa (“true animals”, exhibit
symmetry, represented by remainder of
Kingdom Animalia
Porifera (Sponges)
• General form: Two layered cup
(separated by mesohyl), with porocytes
entering into spongocoel, exiting
through osculum
• Outer layer (epidermis) reinforced by
spicules (Si)
• Filter feeding by Choanocytes that line
endodermis
• Transport of materials by Amoebocytes
Second taxonomic dichotomy
• Radial versus bilateral symmetry
– Super-phylum Radiata exhibits radial
symmetry. Two phyla include:
• Cnidaria (jellyfish, anemones, corals and
hydra)
• Ctenophora (combjellies)
– Super-phylum Bilateria exhibits bilateral
symmetry (rest of invertebrata)
Bilateral symmetry leads to...
Cephalization
• Bilateral symmetry implies a directionality
to the animal
• With movement in a specific direction
comes development of sensory
equipment at end that encounters
environment first
• Collection of sensory nervous tissue at
anterior end of animal = cephalization
• Type of symmetry also reflected by
embryonic germ layers seen in
blastula/gastrula:
Ectoderm
Mesoderm
Endoderm
Diploblastic
= Radiata
(endoderm/ectoderm)
Triploblastic
= Bilateria
(endoderm/mesoderm
/ectoderm)
Cnidaria (Jellyfish, etc.)
• Diploblastic, radially symmetrical (i.e. no
cephalization)
• Phylum characterized by cnidocytes
that eject nematocysts
• Gastrovascular cavity (GVC), with one
opening (mouth/anus simultaneously)
• Tentacles to pull prey into GVC
• Some species exhibit alternation of
sexual and asexual forms (e.g. Obelia)
• Classes within Cnidaria include:
– Hydrozoa (e.g. Obelia, Hydra)
– Scyphozoa (jellyfish, e.g. Sea wasp,
Lionsmane, Portuguese Man-o-war)
– Anthozoa: calcareous secretions build an
exoskeleton (e.g. coral, anenomes,
Metridia)
Third taxonomic dichotomy
• Design of body cavity (or lack thereof)
characterizes Bilateria
– Acoelomates lack a body cavity, e.g.
Platyhelminthes (flatworms)
– Body cavities
• Pseudocoelomates have a body cavity lined
by mesoderm-derived tissue on one side only,
e.g. Nematoda (roundworms), Rotifera
• Eucoelomates (coelomates) body cavity is
lined on both sides by mesodermally-derived
tissue (everything else upwards)
Tissue derived from:
Ectoderm
Mesoderm
Endoderm
GVC
Acoelomate
GVC = Gastrovascular cavity
DT = Digestive tract
PC = Pseudocoelom
euC = Coelom
DT
DT
PC
euC
Pseudocoelomate
Eucoelomate
note: true digestive tract first seen in pseudocoloemates
Platyhelminthes (flatworms)
• Triploblastic, bilateral, cephalized
acoelomates that have been flattened
dorso-ventrally
• No internal transport system
• (Use of GVC, with muscular pharynx)
• Some species exclusively parasitic
• Classes of Platyhelminthes include
– Turbellaria (planarians, e.g. Dugesia,
Planaria). Free-living, aquatic. Movement
by cilia, eased by secretion of mucus
– Trematoda (parasitic flukes, e.g.
Schistosoma)
– Monogenea (parasitic flukes)
– Cestoda (parasitic tapeworms)
n.b. Parasitic forms do not possess GVCs
Body cavities have various functions
• Cushions internal organs
• Independence of movement
• Primitive circulatory system
– Transport of nutrients and metabolic wastes,
gaseous exchange
• Basis of hydrostatic skeleton
• Helped development of a true digestive
tract (phylum Nemertea)
Nematoda (Roundworms)
• Cylindrical triploblastic pseudocoelomates
• Some are freeliving saprobes important role in decomposition of dead
organic matter
• Other are parasitic (e.g. hookworm,
Trichinella*)
*hmmm, pork chop
Fourth taxonomic dichotomy
Protostomes
• Spiral/Determinate
cleavage
• Blastoporemouth
• Schizocoelous
development
e.g. Mollusca thru’ to
Arthropods
Deuterostomes
• Radial/Indeterminat
e cleavage
• Blastoporeanus
• Enterocoelous
development
e.g. Echinodermata
and Chordata
Mollusca
• Triploblastic coelomates: body plan
divided into three (foot, visceral mass,
and mantle)
• Mantle may secrete calcareous shell for
protection against dessication and
predators
• Gaseous exchange by gills. In some
cases, gills are modified to filter feed
• Open circulatory system
• Classes of Mollusca include
– Polyplacophora (Chitons, herbivorous
grazers)
– Gastropoda (snails and slugs: mostly
grazers, but some predators—e.g. cone
shells)
– Bivalvia (Bivalves: clams, oysters,
mussels—filter feeders)
– Cephalopoda (shelled—nautilus, or
unshelled—squid, octopus)
Segmentation
• Defined as a system of similar units
• Allows specialization of regions along
body length
• Evolved separately in protostomes
(Annelida, Arthropoda) and
deuterostomes (all Phyla)
Annelida (segmented worms)
• Triploblastic segmented eucoelomates
• Specialization of body regions (e.g. see
digestive tract)
• Closed circulatory system
• Three classes include:
– Oligochaeta (earthworm—Lumbricus)
– Polychaeta (marine segmented worms)
– Hirudinea (leeches)
Arthropoda
• The most successful animal phylum ever
• Characterized by highly developed
cephalization, exoskeleton (made from
armor-tough chitin), division of body into
head, thorax and abdomen
• Open circulatory system, including
haemocoel as well as coelom
• Modified appendages per segment: first
evolutionary development of flight
• Classification of arthropods is complex,
but subphylums include:
– Trilobitomorpha (extinct trilobites)
– Cheliceriformes (spiders, mites and ticks,
scorpions)
– Uniramia (insects)
– Crustacea (crabs, lobsters, shrimp,
copepods)
Chelicerates includes the class Arachnida
• Simple eyes
• Modified appendages into
– walking legs (4 pairs)
– feeding mouthparts, including pedipalps and
fangs (chelicerae), not mandibles
– Spinnerets
Uniramians
• Insects (Insecta), Millipedes (Diplopoda) and
Centipedes (Chilopoda). Have compound
eyes, mandibles, and sensory antennae
• Most insects have developed flight and occupy
most ecological niches
– Gaseous exchange through spiracles and
tracheae
– Waxy cuticle to prevent dessication
– Other dessication defenses through reabsorption
of water from faeces
– Some species undergo metamorphosis
Crustacea
• Mainly marine
• Extensively specialized, jointed
appendages
• Classes include
– Decapoda (crabs, lobsters, shrimp, prawns)
– Copepoda (copepods)
– Amphipoda (amphipods)
– Isopoda (isopods)
Deuterostomes: Echinodermata
• Triploblastic coelomates
• Pentaradially symmetrical as adult, but
bilaterally symmetrical as larva
• Unique water vascular system
• Classes include:
– Asteroidea (sea stars)
– Echinoidea (sea urchins and sand dollars)
– Holothuroidea (sea cucumbers)
The invertebrate chordates
• Phylum Chordata traditionally thought
of as a vertebrate group, but two of the
three subphyla are invertebrate:
– Urochordata (sea squirts, tunicates)
– Cephalochordata (lancelets, e.g.
Amphioxus)
• All chordates (including vertebrates)
share the common features of
pharyngeal slits, muscular post-anal tail,
notochord and dorsal hollow nerve cord
Protistan Ancestor
(Choanoflagellate)
Asymm etri cal
Parazoa
Porifera
Symmetrical
Eumetazoa
Radiata
Dipl obl asti c
Cnidaria
Bil ateri a
T ri ploblastic
Acoel om ate
Platyhelminthes
Coelomates
Pseudocoelomate
Nematoda
Eucoelomate
Protostome
Mollusca
Annelida
Arthropoda
Deuterostome
Echinodermata
Chordata