What is an Animal?What is an Animal?

3. Nervous tissue & muscle tissue

1. Multicellular, heterotrophic eukaryotes that ingest food: (Metazoa).(Metazoa).

4. Life history (mostly):diploid dominates, sexual w/ small flagellated sperm & large immobile egg cleavage, blastulation, gastrulation … Fig 32.1

2. Cells a) lack cell wallsb) supported by collagen (ch 7 & Fig 40.2)

c) unique intercellular junctions: tight junctionsFig 7.30 desmosomes

(except Porifera) gap junctions

+. Glycogen: (Fig 5.6) carbohydrate store.

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.

Fig

5.2

5

Small SubUnit (SSU) & Large SubUnit (LSU) RNA(or DNA that codes it)are important character statesin molecular phylogenetics.

the ‘outgroup’

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.)

mollusk

echinoderm

urochordate

chordate

platyhelminth

the ‘outgroup’

Similarbut not

identical

Fig. 2.   …strict consensus of two MP trees {Maximum Parsimony = most simple} based on combined SSU and LSU data.

mollusk

echinoderm

urochordate

chordate

platyhelminth

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. 32.8

no - differentiated tissues - yes

1

radial vs bilateral symmetry w/ cephalizationEchinoderms secondarily radial 2

‘Body Plans’Fig 32.8: the newmolecular phylogeny

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blastopore mouth first anus first

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exoskeletonLophophore on larvae

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 …

http://www.amsci.org/amsci/articles/97articles/Erwin-7.html

the radiation {of animals} … through the Cambrian explosionCambrian explosion … a mere 40 million years. … the most extraordinary pace … in the fossil record,

3 explosions?

Fig

32.

14

If compare Fig 32.1 (Ontogeny) to Fig 32.3 (Phylogeny - hypothetical),

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.), …

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 HoxHox genes genes (Fig 21.15) and there are similarities in ontogeny

across species.

looks like ‘Ontogeny Recapitulates Phylogeny’‘Ontogeny Recapitulates Phylogeny’?

… 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 can be seen in other Hox genes as one goes from more primitive to more advanced animals and body plans. …

In the developing embryo, an animal's body plan emerges under the guidance of developmental control genes, including a cluster called the the HoxHox genes genes. Modifications in body plans arise from modifications - duplications and subsequent sequence changes- of developmental genes, such as those found in Hox clusters.

©American Scientist http://www.amsci.org/amsci/captions/captions97-03/Erwin-cap9.html?138,96

Fig 21.15

http://129.137.140.39/freshman/bio103/diverse/camb/choanoflagellate.htm

Choanoflagellates … The structure of the single cell resembles the feeding cells (choanocytes) of living sponges, often thought to be the most ancient living animals.

C&R Fig 28.26

Monophyletic origins of the metazoa: an evolutionary link with fungi.Wainright et al. Science 1993 Apr 16;260(5106):340-2

http://megasun.bch.umontreal.ca/protists/salp/summary.html

… 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 animals and fungi share a unique evolutionary history and that their last common ancestor and that their last common ancestor was a flagellated protist similar to extant choanoflagellates.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}

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 Metazoaclassify the Porifera as true Metazoa. …

1

http://www.amsci.org/amsci/articles/97articles/Erwin-3.html

Morphological and molecular evidence agree that the most primitive of living animal phylathe most primitive of living animal phyla are the sponges (Phylum Porifera).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.

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.}

1

SymmetrySymmetry

Associated with bilateral symmetrybilateral symmetry is cephalizationcephalization, 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 mouth is surrounded by tentacles studded with microscopic stinging capsules known as nematocysts.nematocysts.The cnida, or nematocyst, is the sine qua non of the phylum …

The exclusively aquatic phylum

CnidariaCnidaria is represented by polypspolyps such as sea anemones and corals, and by medusaemedusae such as jellyfish. A polypoid or a medusoid cnidarian is a radially symmetricalradially symmetrical, uncephalized animal with a single body opening, the mouth.

3

Body cavities Body cavities in bilateria

3

Fig

32.

6

Annelids & arthropods are protostomes but they develop a coelom like a deuterostome{primitive coelom NOT lost}.

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’}

coelomate

coelomate

3

coelomate

coelomate

Patterns of development Patterns of development in bilateria

That’s us –anus 1st

(the flatworms)The simplest animals that are bilaterally symmetrical and triploblastic (three cell layers)

a) Non-parasitic Tubellarians:

b) Monogenean fish parasites:

c) Trematode flukes:

Table 33.2, Classes:

d) Cestode tapeworms:

Marineflatworms

FreshwaterPlaneria

Flatworms have no body cavityno body cavity other than the gut and lack an anuslack an anus; the 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. 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 MolluscaPolyplacophora (chitonschitons) Marine; shell with eight plates; foot used for locomotion; head reduced

Gastropoda (snails, slugssnails, 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, oystersclams, mussels, scallops, oysters) Marine and freshwater, flattened shell with two valves; head reduced; paired gills; filter-feeders; mantle forms siphons.

Cephalopoda (squids, octopuses, chambered nautilusessquids, 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: Cephalopod & vertebrate eyes:

a notable example of convergent evolutionconvergent evolution

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

Their basic design is very similar but their Their basic design is very similar but their development shows them to be non-homologousdevelopment shows them to be non-homologous.

Table 33.4 Polychaetes Hirundae Oligochaetes

Two evolutionary adaptations are well developed in this phylum: the coelom and segmentation.

Northern forests 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).

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. Courtesy University of Minnesota, Agricultural Experiment Station

Soil nematodes are major crop pests

Why we don’t eat pork rare:

Trichinella spiralis Muscle Biopsy

Nematodes possess digestive, nervous, excretory, & reproductive systems, but lack a discrete circulatory or respiratory system.Their digestive system has two openings - at the mouth and anus. {which 1st?}

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;

C. elegans has become a model organismfor 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 excitingnew, mysterious and exciting. … the fields which we should now enter are development and the nervous systemdevelopment and the nervous system. …… it was some time before C. elegansC. elegans was selected 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: a self-fertilizing hermaphrodite and a male. Of the 959 somatic cells959 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.17,800 distinct genes.

C&R Fig 21.4: Fate maps of developing cells

1. ‘jointed feet’ 2. exoskeleton 3. segmentation

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.

2/3 of all named organisms on earth are arthropods

J.B.S. Haldane

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.

Trilobites extinct

anemoneshrimp

Palaemonias ganteri (Mammoth cave)

1

2

3

4

The Four Great Lineages

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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.

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.