biol 201 chp 4: introduction to metazoa
DESCRIPTION
This is a lecture presentation for my BIOL 201 Invertebrate Zoology students on Chapter 4: Introduction to Metazoa (Invertebrate Zoology, 7th Ed. by Ruppert, Fox, & Barnes, 2004). Rob Swatski, Assistant Professor of Biology, Harrisburg Area Community College - York Campus, York, PA. Email: [email protected] visit my website, BioGeekiWiki, for more biology learning resources: http://robswatskibiology.wetpaint.comVisit my Flickr photostream for anatomy model photographs! http://www.flickr.com/photos/rswatski/Thanks for looking!TRANSCRIPT
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BIOL 201: Invertebrate Zoology
Chapter 4: Introduction toMetazoa
Rob SwatskiAsst. Prof. Biology
HACC-York1
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Metazoans
Animals in Kingdom Animalia
Multicellular
1-30 million species in 29 major phyla
Colonial protozoan ancestors are
choanoflagellates (sister taxon) 2
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Metazoan Characteristics
Eukaryotic heterotrophs
Larger bodies: costs/benefits?
Most motile (even sessile adults have
motile larvae)
Anterior-posterior polarity; oral-aboral
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Anterior
Posterior4
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Oral
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Aboral
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Metazoan Ground
Plan
Specialized cells organized as tissues
(division of labor)
Primary (original) tissues: epithelial &
connective
Epithelium: sheets of cells bound to each
other by cell-adhesion molecules
Cuticle: surface coat of glycoproteins or
secreted extracellular matrix (ECM) 6
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Connective Tissue
Widely separated, nonadjoining cells in ECM of proteoglycan
gel with collagenproteins
Skeleton: support, protection, muscle
attachment
Exoskeleton: thickened outer
cuticle with proteins or minerals
Endoskeleton: internal stiffening of ECM with
cross-linking (cartilage) or mineral
secretion (bone)8
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Asexual (Clonal)
Reproduction
Budding
Fragmentation
Fission
Parthenogenesis: development of
individual from an unfertilized egg (virgin
birth)9
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Fragmentation 10
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Parthenogenesis 11
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Sexual Reproduction
Diploid adults form haploid gametes(egg & sperm) via
meiosis
Fertilizationdiploid zygote
Zygote divides by mitosis into an
embryo (ontogeny)
Embryo divides by cleavage early
cells called blastomeres
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Embryo Development
Blastula: 1-cell layer thick hollow or solid ball
of cells
Gastrulation:invagination of one wall of blastula 2-layered
gastrula
Morphogenesis
Ectoderm & endoderm(primary germ layers)
form around gelatinous blastocoel
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Indirect Development
Life cycle includes a larval stage
Larva: independent stage with different
anatomy & niche
Biphasic life cycle:benthic adult &
planktonic larva value?
Larva settles in suitable habitat & undergoes
metamorphosis into an immature juvenile 15
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Direct Development
Embryo develops directlyinto juveniles without a
larval stage
Juvenile resembles a miniature version of the
adult (grasshoppers)
Considered to be a derived trait
Indirect development with external fertilization & planktonic larva is the
ancestral pattern16
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Reproductive Adaptations
Improve chances of fertilization & embryo
survival: increase synchrony & proximity
Hermaphroditism: common in species
with small population densities & sessile
lifestyles
Any nearby individual is a potential mate
Most hermaphrodites cross-fertilize rather than self-fertilize
why?17
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Maternal Provisioning
Adaptations providing physical protection &
nutrients to offspring are very valuable
Oviparous: eggs spawned before or just after
fertilization
Viviparous: internal fertilization, embryos
gestate in maternal body, & release larva or
juveniles
Brooding: eggs released from mother, but are
retained on or taken back into her body
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Oviparous aphids
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Viviparous pea aphids
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Spider with her brood
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Body Size & Division of
Labor
Most metazoans are 0.5 mm – 1 m in size
Prokaryote (seed) Protozoan (grapefruit)
Animal (stadium)
Cell specialization improves efficiency
Requires functional compartmentalization &
cellular integration (started with protozoans)
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Hierarchy of Functional Compartments
OrganismOrgan system
Organ
Tissue
Cell
Organelle
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Surface Area-to-Volume
Ratio
SA:V is significantly affected by increases
in body size
As a cell grows larger, its area is squared & its volume is cubed
Eventually, SA (supply) will not be able to
support cell volume (demand)
Limits exchange of gases, nutrients, &
wastes24
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6:1 0.6:1 0.006:1
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Adaptations That Increase
SA:V
Microvilli, pseudopodia, &
internal membranes
Tissues arranged as thin 2-D sheets around
a metabolically inert ECM core
Body plans that are flat & thin or long &
slender
Fractal body plans: tubes in tubes
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Size & Transport
Rates of diffusion slow drastically over great
distances
Effective diffusion distance is roughly 0.5 mm for most animals
Body diameters larger than 1 mm may be diffusion-limited
Circulatory system needed for bodies larger than 1 mm in diameter
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Size & Metabolism
Metabolic rate increases with body size
However, 1g of shrew tissue consumes more
power than 1g of elephant tissue
Poikilotherms (cold-blooded animals)
consume 8 times more mass-specific energy
than protozoans
Homeotherms(mammals & birds)
consume 29 times more energy than a
poikilotherm of equal mass 32
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Advantages of Large Body
Size
Mass-specific decrease in metabolic rate
Reduced risk of predation by protozoa
Larger metazoans can prey upon protozoans
Motile metazoans move faster than protozoans
Multicellularity allows ability to regenerate
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Ontogeny & Phylogeny
Metazoan ontology includes developmental stages subject to natural
selection
Heterochrony: changes in the timing of
developmental events –allows potential for evolutionary change
Two types of heterochrony
Pedomorphosis & Peramorphosis
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Pedomorphosis
A trait of a descendent species resembles an
ancestral larval or juvenile developmental
trait
Results in smaller & simpler descendents with short generation
times
Common in species living in unpredictable
or changing environments
Adapted to colonize entirely new habitats
(interstitial descendents of polychaete worms)
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Cockroach nymphs
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Peramorphosis
A trait of a descendent species that develops
beyond the ancestral trait
Results in larger & more complex descendents
with longer generation times
Favored in constant or predictable environments
(deep sea, coral reefs)
Larger body size is a major trend in metazoan
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Colossal Squid (Mesonychoteuthis)12-14 m long!
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Origins of Metazoa
Colonial theory: Metazoans are derived
from colonial flagellated protozoans
Most widely accepted theory, supported by
morphological & molecular data
Choanoflagellates & Metazoa are sister taxa
Spherical colony of flagellated cells divided by mitosis, but daughter
cells held within ECM41
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Proterospongia sp.
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Creditsby Rob Swatski, 2010
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