BL 4 Intro to animal phyla.pptx

INTRODUCTION TO ANIMAL DIVERSITY  Diversity has to do with the different variety or forms of animals in existence (smallest – largest)  One key challenge terrestrial animals face is variation in temperature  Why - Weak structure of chemical bonds regulating proteins and enzym...

INTRODUCTION TO ANIMAL DIVERSITY  Diversity has to do with the different variety or forms of animals in existence (smallest – largest)  One key challenge terrestrial animals face is variation in temperature  Why - Weak structure of chemical bonds regulating proteins and enzymes  Change in temperature alters them and their functions Adaptations  Some maintain body temperature within a narrow range irrespective of external temperature change (endotherms – birds and mammals)  Others allow their body temperature to conform to the surrounding temperature (ectotherms)  Reason – cost of energy production GENERAL FEATURES OF ANIMALS  Unicellular or Multicellular Heterotrophy: They depend on plants for their food  Divers in Form: They are diverse in form with about 98% of them invertebrates. They range in size from microscopic to very giant sizes.  Majority of animal phyla are found in the sea>freshwater>land.  Arthropoda, Mollusca and Chordata dominate terrestrial animal life. No Cell walls:  They lack rigid cell walls and more flexible.  Their cells join together to form tissues for a particular function (nerve tissues) Active Movement  The ability of different animals to move from place to place is a striking feature the group  Reason: Flexibility of cells and evolution of nervous and muscular tissues  Interesting among such is flying – insects, Sexual Reproduction  Most animals reproduce sexually  Egg are non motile and usually larger than the flagellated sperm cell  With few exceptions there is no alternation of generations (gemetphyte and sporophyte stage) Embryonic Development  Most animals have a similar pattern of embryonic development  Zygote undergoes mitotic division (cleavage) to form a solid ball of cells (Morula) to Blastula (hollow ball of cells)  In some animals an opening (Blastophore) may be formed. The embryo at this stage is called Gastrula  Later growth of cells of the gastrula form the digestive system which vary from phylum to phylum Two main subkingdoms  Parazoa – They lack symmetry, tissues and organs the sponges – Porifera  Eumetazoa  Animals that have symmetry and definite shape  In most cases tissue are organized into organ systems  Animals are primarily classified according to morphological and developmental characteristics, such as a body plan. One of the most prominent features of the body plan of true animals is that they are morphologically symmetrical.  This means that their distribution of body parts is balanced along an axis.  Additional characteristics include the number of tissue layers formed during development the presence or absence of an internal body cavity,  and other features of embryological development, such as the origin of the mouth and anus. Figure 1: The phylogenetic tree of animals based on morphological, fossil, and genetic evidence.  All eumetazoans form distinct embryonic layers that differentiate into adult tissues during development  Diploblastic - two layers – ectoderm and endoderm eg Radiolarians  Triploblastic - have three layers inclusive of the mesoderm KEY Transitions in Animal Body Plan Evolution of Tissues First key transition in animal body plan  The simplest animals lack defined tissues and organs (parazoans).  They exist as aggregate of cells with minimal intercellular interaction eg sponges  Eumetazoans have distinct tissues and specialized cells Evolution of Bilateral symmetry  Sponges lack definite symmetry but others have shape which can be defined along an imaginary axis  Animals with symmetry are either Radiata or Bilateria  Radial Symmetry:  Body design where parts of the body are arranged around a central axis such that any plane passing through the central axis divides the organism into mirror images eg the Cnidarians - jellyfishes  Bilateral symmetry  It’s a body design in which the right and left halves are mirror images when divided through the median saggital plane.  Bilaterians have body plan described as dorsal and ventral portions  They also have the anterior and posterior regions  Bilateral symmetry constitute the second major evolutionary advancement in the animal body plan  It allows parts of the body to evolve in different ways locating different organs in different parts of the body  Bilateria move from place to place efficiently compared to Radiata.  Due to better mobility bilateria are efficient in seeking for food, locating mates and avoiding predators  During early evolution of bilateria, adaptive features for capturing food and evading enemies were grouped at the anterior part  Greater number of sense organs are seen in the bilateria than the radiata  Nervous system in bilateria are mainly in longitudinal nerve cords  Early evolutionary advance had nerve cells grouped around anterior region for transmission of impulses to other parts of the body  This trend led to cephalization – evolution of head and brain area Evolution of Body cavity  Third key evolution in the animal body plan  Efficient organ system was not done until cavities emerged  Cavities are for supporting organs, distributing materials and fostering complex interactions  The presence of the cavity allows digestive tracts to be larger and longer  Longer passage allows for storage of undigested food, longer exposure to enzymes for complete digestion  Such arrangement allows the animal to eat well and then hide during the digestive period limiting exposure  Flexible tube within digestive arrangement enabling freedom of movement  Body cavities also provide good space for the gonads to expand enabling accumulation of many egg and sperm cells  Such storage capacity enable diverse modification of breeding styles among phyla  Large number of gametes can be stored and released when conditions are favourable Types of body Cavities in Bilateria Acoelomate  They have no body cavity Pseudocoelomate  Have a body cavity called pseudocoel located between the mesoderm and the endoderm Coelomate  Body organisation in which the fluid filled cavity (coelom) is located within the mesoderm. In coelomates, gut is suspended within the coelom  Coelom is in turn surrounded by a layer of epithelial cells derived from the mesoderm  Portion of epithelium covering outer wall of coelom – Parietal Peritonium while Portion covering internal organs suspended within the cavity - Visceral Peritonium  In coelomates, the gut is surrounded by tissues acting as a barrier to diffusion – hence development of circulatory system (nutrient, O2 and CO2)  Open circulatory system – blood is pumped into body cavities or hemocoel to reach cells and tissues bathed in it.  Closed circulatory system – Blood is physically separated from other body fluids so can be controlled. Flow is faster and more efficient Fig1: Three Body plans for Bilaterians Evolution of Protostome and Deuterostome  They are coelomates but differ in their embryonic development  Early in embryonic development, a blastopore is formed  The blastopore of the Protostome becomes the animals mouth and the anus develops at the other end  In deuterostmes the blastopore becomes the animals anus and the mouth develops at the other end  Cells of a deuterostome can develop into a complete organism but no one embryonic cell of the protostome can, due to content of regulatory signal in them Fig 2: Protostomes and Deuterostomes The coelom of most protostomes is formed through a process called schizocoely, meaning that during development, . a solid mass of the mesoderm splits apart and forms the hollow opening of the coelom. Deuterostomes differ in that their coelom forms through a process called enterocoely. Here, the mesoderm develops as pouches that are pinched off from the endoderm tissue. These pouches eventually fuse to form the mesoderm, which then gives rise to the coelom Protostomes undergo spiral cleavage, meaning that the cells of one pole of the embryo are rotated, and thus misaligned, with respect to the cells of the opposite pole. This is due to the oblique angle of the cleavage. Deuterostomes undergo radial cleavage, where the cleavage axes are either parallel or perpendicular to the polar axis, resulting in the alignment of the cells between the two poles. Evolution of segmentation  This has to do with subdivision of the body into segments, also known as metamerism  During early development segments are more obvious in the mesoderm but later reflected in the ectoderm and endoderm.  True segmentation is found in annelids, arthropods and chordates Advantages of early embryonic segmentation  In well segmented animals each segment may develop a complete set of organ system  Other segments will duplicate the functions of a damaged segment  Locomotion is more effective when each segment moves independently due to flexibility