Origin and Diversification of Animals

Origin and Diversification of Animals

• Animals display a wide range of body plans, differing in symmetry, body cavities, segmentation, and cephalization.

• Invertebrates encompass various groups, including sponges, cnidarians, lophotrochozoans, ecdysozoans, echinoderms, and hemichordates, each exhibiting unique origins and evolutionary paths regarding organ development.

• Vertebrates feature diverse evolutionary lineages, from tetrapods to amniotes, mammals, and ultimately humans. This section also includes discussion of the evolution of major organ systems within these groups.

Animal Nutrition

• Essential nutrients are critical for proper animal function.

• Food processing involves stages, including ingestion, digestion, absorption, and assimilation.

• Invertebrates and vertebrates demonstrate variation in their digestive systems.

Circulation and Gas Exchange

• Respiratory and circulatory systems are integrated.

• Respiratory pigments facilitate oxygen transport. Different respiratory systems (gills, trachea, vertebrate lungs) are described and compared.

• Vertebrate circulation includes the heart's anatomy, the ECG, the cardiac cycle, and the regulation of cardiac output, blood pressure, gas transport, and blood pH.

Osmoregulation and Excretion

• Osmoregulation maintains water and ion balance. This includes discussions about osmoregulators and osmoconformers in different environments.

• Human excretory systems act as a model for studying processes like glomerular filtration, tubular reabsorption, secretion, counter-current mechanisms, and regulation by hormones.

Nervous System, Sensory, and Motor Mechanisms

• Neuron structure and function are key topics, including action potentials, sodium-potassium pump function, and calcium pump function.

• The nervous system's role in transmission at the synapse and neurotransmitters are discussed.

• Sensory systems, such as the eye (retinal components, photoreceptors) and ear (cochlea, basilar membrane), are detailed.

• Detailed coverage of muscle contraction and relaxation mechanisms is provided, including energetics associated with the process.

Endocrine System

• An overview of the endocrine system, including how hormones act as chemical coordinators, is provided.

• The neuro-endocrine system is described.

Reproduction

• Various reproductive modes, including asexual reproduction, parthenogenesis, and aspects of sexual reproduction, are explored.

• Mammalian reproduction is studied as a model of sexual reproduction.

• The section includes discussions of the reproductive physiology of males and females, fertilization, pregnancy, childbirth, and special topics like AIDS and contraception.

What Characteristics Distinguish Animals?

• Multicellularity is a key animal characteristic differentiating them from bacteria, archaea, and most protists.

• Animal life cycles follow complex patterns of development from unicellular zygotes into multicellular organisms.

• Heterotrophic metabolism is a distinguishing feature. Animals obtain nutrients from their environment or with symbiotic aid.

• Internal digestion allows digestion within the animal's internal gut.

• Movement is a defining characteristic for the vast majority of animals. It is crucial for locating/procuring food.

How Do We Know Animals Are Monophyletic?

• Some animals don't move throughout their life cycle, while other plants and fungi have limited movement. The presence of a gut is also variable among animals.

• Multiple factors consolidate the idea that animals are monophyletic, encompassing all organisms in a single clade.

Animal Monophyly

• The most compelling evidence that animals share a common ancestor arises from phylogenetic data analyses of gene sequences.

• Morphology also helps determine the evolutionary relationship between various animal groups.

Surprisingly Few Shared Morphologic Features

• Unique cell junctions (tight, desmosome, and gap) distinguish animals.

• Extracellular matrix molecules (collagen, proteoglycans) are a common feature in all animal groups.

Common Ancestor of Animals

• The common ancestor of animals is likely a colonial flagellated protist similar to existing colonial choanoflagellates.

• Cells in this ancestral organism likely began to exhibit specialization related to different functions, leading to multicellularity.

Common Ancestor of Animals

• Coordination among cell groups in the common ancestor would likely have improved through specific regulatory and signaling molecules.

• The evolution of these molecules guided differentiation and cell migration in developing embryos leading to more complex organisms.

A Few Basic Developmental Patterns

• Differences in embryonic development patterns were historically used to classify animal groups.

• Analyses of gene sequencing data are increasingly important in differentiating and understanding animal phylogeny.

Cleavage

• The initial cell divisions of a zygote are referred to as cleavage (Radial and Spiral divisions).

• In general, the number of cells in the embryo doubles during cleavage.

• Different cleavage patterns exist among animals.

Gastrulation Stages

• Protostomes and deuterostomes are differentiated based on the development of the mouth and anus.

• Gastrulation is characterized by the formation and migration of germ layers—ectoderm, mesoderm, and endoderm—crucial for subsequent development into complex multicellular organisms.

Germ Layers

• Distinct germ layers form early in development, differentiating into numerous organs.
• Ectoderm gives rise to the skin, hair, nervous system, etc.
• Mesoderm gives rise to the circulatory system, muscle, and excretory organs.
• Endoderm gives rise to the digestive and respiratory systems and related organs.

Sponges

• Sponges lack true germ layers and are relatively simple multicellular organisms, exhibiting two primary cell layers (pinacoderm and choanoderm).

Animal Body Plans

• Animal body plans vary, yet they can often be categorized based on four key features: symmetry, body cavity structure, segmentation, and external appendages.

Symmetry

• Most animals are symmetrical, meaning they can be divided into similar halves along a plane or multiple planes.

• Asymmetry is seen in some early animal lineages such as Placozoans and sponges.

Sponges, Placozoans, Ctenophores, and Cnidarians

• These animal phyla have unique evolutionary characteristics, that were historically less detailed than other groups. Further work is ongoing to determine the evolutionary relationship between these groups.

Cnidarians

• Cnidarians are carnivores, possessing unique specialized cells with stinging nematocytes, enabling them to capture prey.

Explore the fascinating evolution of animals, from invertebrates to vertebrates. This quiz covers key concepts including animal body plans, nutrition, and the integrated systems of circulation and gas exchange. Test your knowledge on how these systems have developed across different species.