Comparative Anatomy Lecture Notes 2022-2023 PDF

COMPARATIVE ANATOMY (ANA3212) LECTURE NOTE By I.A. Tela Department of Anatomy, Faculty of Basic Medical Sciences, College of Health Science, Bayero University, Kano. Second Semester, 2022–23 Academic Session.  L...

COMPARATIVE ANATOMY (ANA3212) LECTURE NOTE By I.A. Tela Department of Anatomy, Faculty of Basic Medical Sciences, College of Health Science, Bayero University, Kano. Second Semester, 2022–23 Academic Session.  LECTURE – III PRICIPLES & CONCEPTS OF COMPARATIVE ANATOMY  Principles of Comparative Anatomy Symmetry & Segmentation Cephalization Body plans IA Tela 3  Symmetry & Segmentation Symmetry: this means that animals body parts are the same in size, shape, and position on either side of a dividing line or central axis (i.e. mirror image of one another). The symmetry of an animal body is one of its most salient features: it inherently characterizes the body plan. Sponges and placozoans are two groups that comprise animals with asymmetrical bodies, even if some smaller poriferan groups like calcareous sponges build symmetrical bodies. Symmetry & Segmentation…  Symmetry & Segmentation… All other animals are characterized by some kind of overall body symmetry, and these are of only a few types: radial, bi-radial and bilateral symmetry. When an endless or a great but finite number of symmetry axes can be drawn through a body, then it is said to be spherically symmetrical. The symmetry plane is an imaginary plane which theoretically divides the body into two equal parts. When the body has one symmetry axis through which several symmetry planes may pass, it is said to have radial symmetry. IA Tela 6 Symmetry & Segmentation… IA Tela 7  Symmetry & Segmentation… Segmentation is the serial repetition of similar organs, tissues, cell types or body cavities along the anterior-posterior (A-P) axis of bilaterally symmetric animals (bilaterians). The definition of segmentation has often been linked to coelom formation. The coelom is a secondary body cavity of mesodermal origin, found in most bilaterian animals. It is fluid filled, and its ancestral function may have been that of a hydrostatic skeleton. Segmental repetition of coelomic cavities might have allowed early worm-like creatures to swim efficiently or burrow through sediments. IA Tela 8  Symmetry & Segmentation… Without segmentation, organisms would lack sophisticated means of movement and complex body structures that enable advanced functions. Segmentation provides the means for an organism to travel and protect its sensitive organs from damage. The ability to divide functions into different portions of the body allows an organism to perform increasingly complex activities and use different segments to perform varying functions. IA Tela 9  Cephalization Cephalization is defined as the evolutionary trend toward nervous system centralization and the development of a head and brain. Fully cephalized organisms have a head and brain, while less cephalized animals display one or more regions of nervous tissue. Cephalization is associated with bilateral symmetry and movement with the head facing forward. Cephalized organisms display bilateral symmetry. Sense organs or tissues are concentrated on or near the head, which is at the front of the animal as it moves forward. The mouth is also located near the front of the creature.  Cephalization… Cephalization is an evolutionary trend in which, over many generations, the mouth, sense organs, and nerve ganglia become concentrated at the front end of an animal, producing a head region. This is associated with movement and bilateral symmetry, such that the animal has a definite head end. Significance: an obvious advantage of cephalization is the development of a control center or brain. The brain is a concentration of nervous tissue that coordinates and controls sensory information and nervous activity. A larger brain allows for smarter and more complex animals.  Cephalization… Advantages of cephalization are development of a complex neural system and intelligence, clustering of senses to help an animal rapidly sense food and threats, and superior analysis of food sources. Cephalization offers an organism three advantages. i. it allows for the development of a brain. The brain acts as a control center to organize and control sensory information. Over time, animals can evolve complex neural systems and develop higher intelligence. ii. sense organs can cluster at the front of the body. This helps a forward-facing organism efficiently scan its environment so it can locate food and shelter and avoid predators and other dangers. Basically, the front end of the animal senses stimuli first, as the organism moves forward. iii. cephalization trends toward placing the mouth closer to the sense organs and brain. The net effect is that an animal can quickly analyze food sources. Predators often have special sense organs near the oral cavity to gain information about prey when it's too close for vision and hearing. For example cats have vibrissae (whiskers) that sense the prey in the dark and when it's too close for them to see. Sharks have electroreceptors called the ampullae of Lorenzini that allow them to map prey location. Radially symmetrical organisms lack cephalization. Nervous tissue and senses typically receive information from multiple directions. The oral orifice is often near the middle of the body. IA Tela 12  Cephalization… Three groups of animals display a high degree of cephalization: vertebrates (e.g. humans, snakes, and birds), arthropods (e.g. lobsters, ants, and spiders), and cephalopod molluscs (e.g. octopuses, squid, and cuttlefish). Animals from these three groups exhibit bilateral symmetry, forward movement, and well-developed brains. Species from these three groups are considered to be the most intelligent organisms on the planet. IA Tela 13  Cephalization… Cephalization doesn't offer an advantage to free-floating or sessile organisms. Many aquatic species display radial symmetry. Examples include echinoderms (starfish, sea urchins, sea cucumbers) and cnidadians (corals, anemones, jellyfish). IA Tela 14  Body plans Body plan is a suite of characters shared by a group of phylogenetically related animals at some point during their development. A body plan, Bauplan (German plural Baupläne), or ground plan is a set of morphological features common to many members of a phylum of animals. A body plan is a collection of major structural features and developmental processes that correspond by homology within a large group of animals. IA Tela 15  Body plans… Traditionally, body plans are identified as unique combinations of character state, including the following: IA Tela 16 Body plans… IA Tela 17  Concepts of Comparative Anatomy Phylogeny & Ontogeny Taxonomy & Systematics Homology & Analogy Adaptation & Natural selection Convergence & Parallel evolution  Phylogeny & Ontogeny Phylogeny: refers to is the study of relationships among different groups of organisms and their evolutionary development. It attempts to trace the evolutionary history of all life on the planet. It is based on the phylogenetic hypothesis that all living organisms share a common ancestry. A closely related branch of science that makes use of phylogenetic tree diagrams to study evolutionary histories and relatedness among various groups of organisms is phylogenetics. The process through which new species is formed from the existing ones is called Phylogenesis or Speciation.  Phylogeny & Ontogeny… Ontogeny (also ontogenesis or morphogenesis) is the origination and development of an organism, usually from the time of fertilization of the egg to the organism's mature form—although the term can be used to refer to the study of the entirety of an organism's lifespan. It primarily focus on the genetic make up of the organism or individual as this is responsible for individuality.  Phylogeny & Ontogeny… The concept of phylogeny and ontogeny is summed up by von Baer which states that features which are common to all members of a major taxonomic group of animals e.g. vertebrates develop earlier in ontogeny than the special features of which distinguished them phylogenetically i.e. into species. This suggest that vertebrates exhibit similar architectural patterns both in structure and development hence, ontogenesis comes before phylogenesis. It also illustrates that in vertebrates early development of notochord, pharyngeal pouches and aortic arches occur in all members of the vertebrates subphylum. This early features then become modified in the direction of the species as development occur.  Phylogeny & Ontogeny… Biogenetic law modifies von Baer’s law which postulated that features or structures that appears earliest in the ontogeny development are oldest phylogenetically as they must have been inherited from the common ancestors, whereas those develop latter in the ontogeny are more recent phylogenetically.  Taxonomy & Systematics These are two concepts related to the study of diversification of living forms and the relationships of living things through time. Taxonomy is the practice and science of categorization or classification. A taxonomy is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. Systematics is involved in the determination of evolutionary relationships of organisms.  Taxonomy & Systematics… Taxonomy also involves describing, naming, and classifying of organisms in biology. It uses morphological, behavioral, genetic, as well as biochemical observations to identify organisms. Different plants, animals, and microorganisms are grouped into different species. IA Tela 24  Taxonomy & Systematics… A species is a potentially interbreeding group of organisms, which produces a fertile offspring. It is considered as the fundamental level of the biological classification of organisms. Starting from the species, organisms are classified into large groups of organism, which are called the taxonomic levels. Species, genus, family, order, class, phylum, kingdom, and domain are the ascending order of the taxonomic levels.  Taxonomy & Systematics… Systematics: is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Therefore, the systematics consists of both taxonomy and evolution. Systematics uses morphological, behavioral, genetics, and evolutionary relationships between organisms. By using these characteristic features, systematics describes an organism by means of classification, name, cladistics, and phylogenetics. Cladistics refers to the classification of organisms based on the branching of different lineages from a common ancestor. IA Tela 26  Taxonomy & Systematics… Cladistics: refers to a biological classification system that involves the categorization of organisms based on shared traits. Organisms are typically grouped by how closely related. Cladistics can be used to trace ancestry back to shared common ancestors and the evolution of various characteristics.  Taxonomy & Systematics… Phylogenetics: refers to the study of the evolutionary relationship between biological entities. IA Tela 28  Taxonomy & systematics… Phenetics: taximetrics, is an attempt to classify organisms based on overall similarity, usually in morphology or other observable traits, regardless of their phylogeny or evolutionary relation. The relationships of the organisms are presented by phylogenetic trees.  Taxonomy & systematics… Analogous structures: have different evolutionary ancestries but they have the same function. Examples of these types of structures are the wings of birds, bats and insects.  Taxonomy & systematics… Homologous organs are those organs which have similar anatomical structure and common evolutionary origin but they perform different functions. For example, the wings of a fly, a moth, and a bird are analogous because they developed independently as adaptations to a common function—flying.  Adaptation and Natural selection ‘Adaptation’ is a process of evolution in which traits in a population are modified by natural selection to meet better challenges presented by the local environment. It can also be defined as a trait or behavior that helps an organism survive and reproduce. IA Tela 32  Adaptation and Natural selection It is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift. It can also be defined as the process that explains this survival and shows how species can change over time.  Adaptation and Natural selection… Natural selection: is the process through which populations of living organisms adapt and change. It is also defined as the differential reproduction of genotypes which produces phenotypic variation in some component of fitness, such as survival or mating success etc. IA Tela 34 Adaptation and Natural selection…  Adaptation and Natural selection… An adaptation is a phenotypic trait moulded by natural selection. Natural selection The trait could be physiological, behavioural, developmental or morphological, or it could be a life history trait. It is the physical or behavioural characteristic of an organism that helps an organism to survive better in the surrounding environment. IA Tela 36  Adaptation and Natural selection… Physical Adaptations/Traits ✓Color: Camouflage (adaptation that allows animals to blend in with certain aspects of their environment.) ✓Beaks (food gathering) ✓Claws (food gathering, protection) ✓Sensory abilities (sight, smell, taste, touch, hearing) ✓Mimicry (close external resemblance of an animal or plant (or part of one) to another animal, or plant generally to avoid or deter predators). IA Tela 37  Adaptation and Natural selection… Behavioral Adaptations Migration Hibernation Traveling in herds Hunting in packs Nocturnal (active at night) Instincts (running, hiding, building nests) Learned behaviors Communication IA Tela 38  Convergent & Parallel Evolution Groups of organisms or species undergo natural selection over time due to environmental pressure, giving rise to different patterns of evolution. Parallel evolution, divergent and convergent evolutions are the three main patterns of evolution. IA Tela 39  Convergent & Parallel Evolution… Divergent evolution differs from the other two evolutionary patterns as it forms distinct species from a common ancestor species.  Convergent & Parallel Evolution… Convergent evolution This is generally considered to be the production of similar traits by different generative systems. It is also referred to as the independent evolution of analogous structures in unrelated species. It occurs when unrelated species live in the same habitat. It gives rise to analogous traits in unrelated species as an adaptation to the similar environmental pressure. Though the anatomical structure is different in analogous traits, they are functionally similar. IA Tela 41  Convergent & Parallel Evolution… Emergence of wings in birds, bats, and insects as an adaptation to fly. The body shape of dolphins and sharks. Though the two are distantly related animals, their body shapes are adapted for fast swimming. Thus, the environment forces the phenotype of distantly related organisms to become analogous. The development of the eye of vertebrates, cephalopods, and cnidarian. The development of analogous structures is referred to as homoplasy. IA Tela 42  Convergent & Parallel Evolution… Parallel evolution This refers to the independent evolution of similar traits in different but, equivalent habitats. It occurs in geographically separated but equivalent habitats. It gives morphological resemblance to two species. Both unrelated and distantly-related species may undergo parallel evolution in equivalent habitats as the environmental influence on the species is similar. IA Tela 43  Convergent & Parallel Evolution… Examples of parallel evolution Wolf, mole, mice, rat, etc (The marsupial mammals of Australia) are examples of marsupial mammals , which are similar to placental mammals elsewhere. The evolution of old world monkeys and new world monkeys. Both old and new world monkeys shared a common ancestor a long time ago. Though they were split apart by the Atlantic Ocean, both old and new world monkeys evolve in a very similar manner. IA Tela 44