1. Overview of Animal Diversity Chapter 31

2. Quick 9 minute Overview I will explain in detail as the presentation goes on http://www.youtube.com/watch?v=wd-QnKlfZHI

3. General Features of Animals Heterotrophs  Animals cannot construct organic material so it must be obtained through ingesting other animals. Animals are herbivores, carnivores, omnivores or detritivores. Multicellular  All animals are multicellular, often with complex bodies.

4. General Features of Animals No Cell Wall  Animals lack cell walls but many cells are instead held together by extracellular lattices of structural proteins (I.E. collagen). While other proteins form a collection of unique multicellular junctions between animal cells. Active Movement  Animals are able to move from place to place. This lead to the flexibility of their cells and the evolution of nerve and muscle tissue.

5. General Features of Animals Diverse in form  Animals are very diverse in size, shape and color. Most animals (99%) are invertebrates (lacking a backbone) while some have a backbone and are called vertebrates. Diverse Habitat  The animal kingdom includes 35 phyla. Most of which occur at sea, less in freshwater and even fewer on land.

6. General Features of Animals Sexual Reproduction  Most animals reproduce sexually. In animals, cells formed in meiosis function directly as gametes. Haploid cells fuse directly with each other to form a zygote. Unique Tissue  The cells of animals (except sponges) are organized into structural and functional unites called tissues, collections of cells that have joined together and are specialized to perform a specific function. Two most important are muscular tissue (power movement) and nervous tissue (conducts signals among cells).

7. General Features of Animals Embryonic Development  Most animals go through similar patterns of development.  The zygote first goes through mitotic division called cleavage and then becomes a ball of cells called morula and then a hollow ball of cells called blastula  It then folds inwards to form a hollow sac with an opening called blastopore  This stage of development is called gastrula.

8. The traditional classification of Animals  Multicellular animals, or metazoans, are traditionally divided into 35 distinct phyla First Branch  Parazoa – animals that lack definite symmetry and possess neither tissues of organs.  Eumetazoa – animals that have definite shape and symmetry and, in most cases, tissues organized into organs Second Branch  Called the emuetazoan branch  Two subgroups  Radiata – (having radial symmetry) have two lays, an outer ectoderm and an inner endoderm, thus called diploblastic  Bilateria – (having bilateral symmetry) are triploblastic and produce a third layer, the mesoderm, between the ectoderm and the endoderm

10. The Five Key Transitions in Body Plan 1.Evolution of Tissue  All animals except the simplest, called parazoa (sponges), have distinct tissues with highly specialized cells. 2. Evolution of Bilateral Symmetry  All animals except Parazoa have a definite symmetry and shape.  Two types of symmetry  Radial symmetry – a body design that is arranged around a central axis in such a way that any plan passing though the central axis divides the organism into halves that are mirror images. Think Jelly Fish

11. The Five Key Transitions in Body Plan Bilateral Symmetry  The body of all other animals is to have bilateral symmetry – a body design in which the body has a right and a left that are mirror images of each other.  It has a top dorsal and a bottom portion called ventral  It has a front called the anterior and an end called the posterior.  They produce three germ layers: an outer, ectoderm (nervous system), an inner endoderm (digestive organs), and a third layer between the other two, mesoderm (muscles)  The evolution of bilateral symmetry has permitted the creation of organs in different parts of the body and has greatly increased mobility.  The development of the nervous system from the ectoderm in the anterior lead to brain being located in the head. This is called cephalization. It increased the dominance and specialization of organs.

12. The Five Key Transitions in Body Plan 3. Evolution of Body Cavity  Efficient Organ systems could not evolve until they had body cavities to support them  Three major types  Acoelomates – have no body cavity  Psuedocoelomates – have a body cavity called the psuedocoel located between the mesoderm and endoderm  Coelmates – a fluid-filled body cavity develops entirely in the mesoderm. Such a cavity is called a coelom

13. The Five Key Transitions in Body Plan Coelomates  A major advantage of coelomate body play is that it allows contact between mesoderm and endoderm, so that tissues can interact during development  The development of coelom poses a problem with circulation. This is solved by the evolution of the circulatory system which is a network of vessels that carry fluids to parts of the body.  Open Circulatory System – the blood passes from vessels into sinuses, mixes with body fluid and then reenters the vessels in another location  Closed Circulatory System – the blood is physically separated from other body fluids and can be separately controlled.  The evolutionary relationship among the types of body cavities remains unclear.

14. The Five Key Transitions in Body Plan 4. The Evolution of Dueterostome Development  Bilaterally symmetrical animals exhibit a pattern of embryonic development that begins with a mitotic cell division of the egg that lead to the formation of a hollow ball of cells called blastula  The blastula indents to form a two-layer-thick ball with a blastopore opening to the outside and primitive gut cavity called the archenteron  Bilaterians are divided into two groups  The protostomes which develop a mouth first  The dueterostomes which develop an anus first

15. The Five Key Transitions in Body Plan Differences between protostomes and dueterostomes  Cleavage – the progressive division of cells during embryonic growth  In Protostomes, each new cell buds off at an angle oblique to polar axis. As a result, a new cell nestles into the space between older ones in a closely packaged array. This is called spiral cleavage  In dueterostomes, the cells divide parallel to and at a right angle to the polar axis. The pairs of cells from each division are positioned directly above and below one another and causes the cells to be packaged in a loose array. This is called radial cleavage  Fate of embryonic cells  Protostomes exhibit determinate development where each embryonic cell has a predetermined fate in terms of what kind of tissue it will form as an adult.  Dueterostomes display indeterminate development where the first few daughter cells produced are identical to the mother cell and anyone of them can develop into a complete organism  Fate of Blastopore  In protostomes the mouth develops first  In dueterostomes the anus develops first  Formation of the Coelom  In protostomes the coelom develops simply and directly. The cells simply move away from one another as the coelomic cavity expands within the mesoderm  In dueterostomes whole groups of cells usually move around to form new tissue associations.

17. The Five Key Transitions in Body Plan The Evolution of Segmentation  Two advantages from early embryonic segmentation  In some organisms (earth worms) each segment may go on to develop a more or less complete set of adult organs  Locomotion is far more effective when individual segments can move independently because the animal as a whole has far more flexibility of movement (think of moving your hand)  Segmentation, also referred to as metamerism, underlies the organization of all advance animal body plans. It is usually apparent in their embryological development.

18. A New Look at the Metazoan Family Tree  The traditional animal phylogeny is being reevaluated because:  The either or aspects of it leave minor groups unaccounted for  The use of DNA and RNA comparison gives better information about the relations of certain species from the field of molecular systematics – the use of unique sequences within certain genes to identify cluster of related groups  Protostomes are placed in two separate clades due to the new molecular research  Expect the animal tree of life to be altered greatly in the upcoming decades as new research is done.

19. Origins of Metazoans  The animal kingdom is monophyletic – that parazoans and eumetazoans have a common ancestor  Three hypothesis of metazoans from single-celled protists:  The multinucleate hypothesis– metazoans arose from a multinuclear protist. The cells later became compartmentalized  The colonial flagellate hypothesis – metazoans descended from a colonial protist, hollow spherical colonies of flagellated cells  The polyphyletic origin hypothesis – sponges evolved independently from eumatazoans  RNA evidence supports the colonial flagellate hypothesis

20. Early Diversification of the Animal Family Tree  Most early life developed around the beginning of the Cambrian Period in the Cambrian Explosion  No new significant innovations in animal body plan has occurred  The reason why no new body plans have occurred is being studied by evo-devo who are scientists that study a synthesis of evolutionary biology and developmental biology  Much of the variation is associated with changes in the location or time or expression of the hox genes within developing embryos