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1. Multicellular, heterotrophic eukaryotes that ingest food: (Metazoa).
What is an Animal?
2. Cells a) lack cell walls
b) supported by collagen (ch 7 & Fig 40.2)
c) unique intercellular junctions: tight junctions
Fig 7.30
desmosomes
(except Porifera)
gap junctions
3. Nervous tissue & muscle tissue
4. Life history (mostly):
diploid dominates,
sexual w/ small flagellated sperm & large immobile egg
cleavage, blastulation, gastrulation … Fig 32.1
+. Glycogen: (Fig 5.6)
carbohydrate store.
Fig 5.25
http://ntri.tamuk.edu/cell/ribosomes.html
s = Svedberg units: the rate of
sedimentation in a centrifuge,
related to molecular weight and
3-D shape … varies across phyla.
Small SubUnit (SSU) &
Large SubUnit (LSU) RNA
(or DNA that codes it)
are important character states
in molecular phylogenetics.
Evaluating hypotheses of basal animal phylogeny
using complete sequences of large {LSU} and small {SSU} subunit rRNA.
Medina et al. 2001. Proc. National Academy Of Sciences USA 98:9707-9712.
Fig. 1. Comparison of ML SSU and LSU trees (A and B, respectively).
ML bootstrap (100 replicates) values are shown at the nodes. < indicates bootstrap less than 50%. (Bar = 0.1 substitutions per site.)
the ‘outgroup’
the ‘outgroup’
Similar
but not
identical
platyhelminth
mollusk
echinoderm
urochordate
chordate
The text’ traditional’ phylogeny (Fig. 32.4), & SSU phylogeny (Fig. 32.8)
closely correspond to the best consensus of ribosomal SSU & LSU data
(note: Medina et al. 2001 didn’t look at all the phyla in Fig. 32.4)
Fig. 2. …strict consensus of two MP trees
{Maximum Parsimony = most simple}
based on combined SSU and LSU data.
platyhelminth
mollusk
echinoderm
urochordate
chordate
Fig. 32.8
Lophophore on larvae
exoskeleton
4
blastopore mouth first
anus first
3
radial vs bilateral symmetry w/ cephalization
Echinoderms secondarily radial 2
no - differentiated tissues - yes
1
Fig 32.8: the new
molecular phylogeny
‘Body Plans’
http://www.amsci.org/amsci/articles/97articles/Erwin-7.html
the radiation {of animals} … through the Cambrian explosion
… a mere 40 million years. … the most extraordinary pace … in the fossil record,
The trigger of the Cambrian explosion(s) is still uncertain …
Whether the burst was the result of an increase in oxygen,
an ecological arms race or something else,
the elaboration of Hox complexes {homeobox genes}
may have been necessary …
Fig 32.14
3 explosions?
If compare Fig 32.1 (Ontogeny)
to Fig 32.3 (Phylogeny - hypothetical),
looks like ‘Ontogeny Recapitulates Phylogeny’?
Haeckel proposed this as a literal law, which it is not.
But ‘scratch a myth and find a truth:’
The evolution of morphology involves the modification
of basic developmental processes
involving ancient Hox genes (Fig 21.15)
and there are similarities in ontogeny
across species.
Ontogeny and Phylogeny is divided into two sections.
The first is the history of the idea of recapitulation …
In the second part Gould presents his own ideas on heterochrony …
acceleration or retardation of different developmental processes
(growth, sexual maturation, morphological changes, etc.), …
©American Scientist http://www.amsci.org/amsci/captions/captions97-03/Erwin-cap9.html?138,96
In the developing embryo,
an animal's body plan emerges
under the guidance of
developmental control genes,
including a cluster called the Hox genes.
Modifications in body plans arise from modifications
- duplications and subsequent sequence changesof developmental genes,
such as those found in Hox clusters.
… the common ancestor to fruit flies and mice
had one gene …
In Drosophila this gene has become
three separate genes (gray, green, orange).
These genes underwent further expansion,
duplication and sequence modifications …
in the mouse
there are a greater number of related genes
to control and direct the formation
of an abdominal region ...
Similar expansions and modifications
Fig 21.15
can be seen in other Hox genes
as one goes from more primitive to more advanced animals and body plans. …
http://megasun.bch.umontreal.ca/protists/salp/summary.html
Monophyletic origins of the metazoa:
an evolutionary link with fungi.
Wainright et al. Science 1993 Apr 16;260(5106):340-2
… comparisons of small subunit ribosomal RNA sequences
describes the evolutionary origin
and early branching patterns of the kingdom Animalia.
From these data, it was inferred that
animals and fungi share a unique evolutionary history
and that their last common ancestor
was a flagellated protist similar to extant choanoflagellates.
Hsp70 sequences indicate that choanoflagellates are closely related to animals.
Snell et al. 2001. Current Biology 11 (12): 967-970 JUN 26 2001
{Hsp = Heat shock proteins}
http://129.137.140.39/freshman/bio103/diverse/camb/choanoflagellate.htm
C&R
Fig 28.26
Choanoflagellates …
The structure of the single cell resembles
the feeding cells (choanocytes) of living sponges,
often thought to be the most ancient living animals.
1
Review:
How was metazoan threshold crossed?
The hypothetical Urmetazoa.
Muller WEG. 2001. Comp Biochem & Physiology A
-Molecular & Integrative Physiology 129:433-460.
Abstract:
… During the last few years,
cDNAs/genes coding for informative proteins
have been isolated and characterized from sponges, …
The analyses of their deduced amino acid sequences
allowed a molecular biological resolution
of the monophyly of Metazoa.
… classify the Porifera as true Metazoa. …
http://www.amsci.org/amsci/articles/97articles/Erwin-3.html
Morphological and molecular evidence agree that
the most primitive of living animal phyla
are the sponges (Phylum Porifera).
Sponges have only a few cell types differentiated
to perform specialized functions, and
they lack the sort of cell-to-cell junctions
that form sheets of tissues in higher forms.
1
Sponges are thought closely related to
the choanoflagellates, and could be
thought of as large colonies …
{a clone of amoebocytes
that build mesohyl,
differentiate into choanocytes
& gametes & distribute food.}
Symmetry
3
Associated with bilateral symmetry is cephalization,
an evolutionary trend toward the concentration of sensory equipment
on the anterior end, the end of a traveling animal that is usually
first to encounter food, danger, and other stimuli.
In most bilateral animals, cephalization also includes
the development of a central nervous system concentrated in the head …
A head end is an adaptation for movement …
The symmetry of an animal generally fits its lifestyle.
Many radial animals are sessile forms (attached to a substratum)
or plankton (drifting or weakly swimming aquatic forms).
Their symmetry equips them to meet the environment equally well from all sides.
Most animals that move actively from place to place are bilateral.
3
The exclusively aquatic phylum
Cnidaria is represented by
polyps such as sea anemones and corals, and by
medusae such as jellyfish.
A polypoid or a medusoid cnidarian
is a radially symmetrical,
uncephalized animal
with a single body opening, the mouth.
The mouth is surrounded by tentacles
studded with microscopic stinging capsules
known as nematocysts.
The cnida, or nematocyst,
is the sine qua non of the phylum …
Fig 32.6
Body cavities in bilateria
The molecular-based
phylogeny suggests that
the bilateral animals
are a monophyletic group
with true coeloms.
In this view
of animal phylogeny,
simpler bilaterians
lacking coeloms
(acoelomates)
and those having
pseudocoeloms
(not completely lined by
mesoderm)
evolved secondarily
from coelomates.
{body cavity is not a
‘shared derived
character’}
Annelids & arthropods
are protostomes
but they develop
a coelom
like a deuterostome
{primitive coelom
NOT lost}.
coelomate
3
coelomate
Patterns of development in bilateria
coelomate
3
coelomate
That’s us –
anus 1st
(the flatworms)
The simplest animals
that are
bilaterally symmetrical
and triploblastic
(three cell layers)
Table 33.2, Classes:
a) Non-parasitic
Tubellarians:
Freshwater
Planeria
Marine
flatworms
b) Monogenean
fish parasites:
Flatworms have no body cavity other than the gut
c) Trematode
and lack an anus; the
flukes:
pharyngeal opening both takes in food and expels waste.
In larger flatworms the gut is very highly branched
in order to transport food to all parts of the body.
d) Cestode tapeworms:
The lack of a cavity
also constrains flatworms to be flat;
they must respire by diffusion,
and no cell can be too far from the outside
Table 33-3. Major Classes of Phylum Mollusca
Polyplacophora (chitons) Marine;
shell with eight plates; foot used for locomotion; head reduced
Gastropoda (snails, slugs) Marine, freshwater, or terrestrial;
asymmetric body, usually with a coiled shell; shell reduced or absent in some;
foot for locomotion; radula present
Bivalvia (clams, mussels, scallops, oysters) Marine and freshwater,
flattened shell with two valves; head reduced;
paired gills; filter-feeders; mantle forms siphons.
Cephalopoda (squids, octopuses, chambered nautiluses) Marine;
head surrounded by grasping tentacles, usually with suckers;
shell external, internal, or absent; mouth with or without radula;
locomotion by jet propulsion using siphon made from mantle.
Cephalopod & vertebrate eyes:
a notable example of convergent
evolution
Their basic design is very similar but their
development shows them to be non-homologous.
Firstly the vertebrate retina is multilayered
with ganglionic cells, bipolar cells,
and photoreceptor cells,
whereas the mollusc retina is a monolayer
of photoreceptor cells.
Secondly the vertebrate retina is inverted
such that the photoreceptors are directed
away from the light and behind the other cell layers.
The mollusc photoreceptors are directed
towards the light and are called everse.
Thirdly the vertebrate retina is formed by
evagination of the neural ectoderm whereas
the mollusc forms from evagination of the ectoderm.
Finally the lens in vertebrates is formed from
transparent lens fiber cells whereas
those of the mollusc are formed by cellular fusions
(Halder et al, 1995b).
http://www.maayan.uk.com/evoeyes2.html
Two evolutionary adaptations
are well developed
in this phylum:
the coelom and segmentation.
Table 33.4 Polychaetes
Hirundae
Oligochaetes
A forest floor without worms (left) and with (right).
Spring flowers and tree seedlings both suffer when
earthworms munch the decaying litter on the ground.
Northern forests
Courtesy University of Minnesota, Agricultural Experiment Station
are under attack
by a silent, invisible
and deadly plague: an army of introduced earthworms.
By rapidly munching decomposing organic crud on the forest floor,
the worms deprive native plants and tree seedlings of a place to germinate and grow.
The result is a bare forest floor, lacking most spring flowers and tree seedlings.
Earthworms are a blessing in gardens, where they mix the soil, increase porosity,
and leave fertile droppings … But … it's not true in ecosystems that are not "used to" worms.
In the upper Midwest, all worms were extirpated
by Ice-Age glaciers that smothered the area until about 11,000 years ago.
And since worms can't travel far under their own steam,
the forests have had essentially no worms.
In contrast, worms reached cities and farms courtesy of settlers who brought plants and soil).
Why we don’t eat pork rare:
Trichinella spiralis
Muscle Biopsy
Among the most widespread of all animals,
roundworms (nematodes) are found in most aquatic habitats,
in wet soil, in the moist tissues of plants, and
in the body fluids and tissues of animals.
In contrast to annelids, nematodes are pseudocoelomates
& the bodies of nematodes are not segmented.
A tough exoskeleton called a cuticle covers the body;
Soil nematodes
are major crop pests
Nematodes possess digestive, nervous, excretory,
& reproductive systems,
but lack a discrete circulatory or respiratory system.
Their digestive system has two openings
C. elegans
- at the mouth and anus. {which 1st?}
has become a model organism
for studying genotype to phenotype
In late 1962, Francis Crick and I began a long series of conversations
about the next steps to be taken in our research.
Both of us felt very strongly that most of
the classical problems of molecular biology had been solved and that
the future lay in tackling more complex biological problems. …
as I put it in a draft paper, "we must move on to other problems …
which are new, mysterious and exciting.
… the fields which we should now enter are
development and the nervous system. …
… it was some time before C. elegans was selected …
This year's Nobel Laureates in Physiology or Medicine
have made seminal discoveries concerning
the genetic regulation of organ development
and programmed cell death.
By establishing the nematode Caenorhabditis elegans
as an experimental model system,
possibilities were opened to follow cell division and
differentiation from the fertilized egg to the adult.
The Laureates have identified key genes regulating
organ development and programmed cell death
and have shown that corresponding genes exist
in higher species, including man.
The discoveries are important for medical research
and have shed new light on the pathogenesis
of many diseases.
C. elegans is a free-living nematode.
There are two sexes:
C&R Fig 21.4: Fate maps of developing cells
a self-fertilizing hermaphrodite and a male.
Of the 959 somatic cells of the hermaphrodite
some 300 are neurons. Neural structures include
a battery of sense organs in the head which mediate
responses to taste, smell, temperature and touch …
… an anterior nerve ring with a ventral nerve cord …
There are 81 muscle cells. …
The development and function of this diploid organism
is encoded by an estimated 17,800 distinct genes.
1. ‘jointed feet’ 2. exoskeleton 3. segmentation
J.B.S. Haldane
2/3 of all named organisms on earth are arthropods
The body of an arthropod is completely covered by the cuticle,
an exoskeleton constructed from layers of protein and chitin.
Cephalization is extensive, w/ well-developed sensory organs, including eyes,
olfactory receptors for smell, and antennae for touch and smell.
Arthropods have open circulatory systems
Most aquatic species have gills.
Terrestrial arthropods generally have internal surfaces for gas exchange.
Most insects, for instance, have tracheal systems.
Many zoologists now prefer to split the arthropods into multiple phyla
corresponding to the four great lineages:
phylum Trilobita, phylum Chelicerata, phylum Uniramia, and phylum Crustacea.
Trilobites
1
extinct
2
3
4
Palaemonias ganteri
(Mammoth cave)
The Four Great Lineages
anemoneshrimp
The echinoderms are definitely bilaterians,
not radiate animals related to cnidarians.
Echinoderm larvae are bilateral.
{& similar to chordate larvae}
The radial anatomy of adult echinoderms
is a secondary adaptation
to a sessile lifestyle.
3
Echinoderms are among the most distinctive of all animal phyla.
diagnosable on basis of the four synapomorphies below.
1. Calcitic skeleton composed of many ossicles.
Embryologically, echinoderm ossicles are a true endoskeleton.
Functionally, however, the majority of ossicles act more like an exoskeleton.
2. Water vascular system - performs many important functions in echinoderms,
including locomotion, respiration, and feeding;
3. Mutable collagenous tissue. The ossicles of echinoderms
are connected by ligaments composed predominantly of collagen.
The material properties of this connective tissue are mutable on short timescales,
under neuronal control. Ligaments are normally "locked" (rigid),
but can be temporarily "unlocked" (loosened). This provides the ability to
maintain a variety of postures with no muscular effort.
4. Pentaradial body organization in adults.
The evolutionary origins of five-fold symmetry remain obscure.
This phylum, to which we belong, consists of
two subphyla of invertebrate animals {Urochordates & Cephalochordates}
plus the subphylum Vertebrata, the animals with backbones.