Bài giảng Biology - Chapter 32: An Introduction to Animal Diversity

Chapter 32An Introduction to Animal DiversityOverview: Welcome to Your KingdomThe animal kingdomExtends far beyond humans and other animals we may encounterFigure 32.1Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layersSeveral characteristics of animalsSufficiently define the groupNutritional ModeAnimals are heterotrophsThat ingest their foodCell Structure and SpecializationAnimals are multicellular eukaryotesTheir cells lack cell wallsTheir bodies are held together By structural proteins such as collagenNervous tissue and muscle tissueAre unique to animalsReproduction and DevelopmentMost animals reproduce sexuallyWith the diploid stage usually dominating the life cycleAfter a sperm fertilizes an eggThe zygote undergoes cleavage, leading to the formation of a blastulaThe blastula undergoes gastrulationResulting in the formation of embryonic tissue layers and a gastrulaZygoteCleavageEight-cell stageCleavageBlastulaCross section of blastulaBlastocoelBlastocoelGastrulaGastrulationEndodermEctodermBlastoporeEarly embryonic development in animalsFigure 32.2 In most animals, cleavage results in theformation of a multicellular stage called a blastula.The blastula of many animals is a hollow ball of cells.3The endoderm ofthe archenteron de-velops into the tissuelining the animal’sdigestive tract.6The blind pouchformed by gastru-lation, calledthe archenteron,opens to the outsidevia the blastopore.5 Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer).4 Only one cleavagestage–the eight-cellembryo–is shown here.2 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage.1All animals, and only animalsHave Hox genes that regulate the development of body formAlthough the Hox family of genes has been highly conservedIt can produce a wide diversity of animal morphologyConcept 32.2: The history of animals may span more than a billion yearsThe animal kingdom includes not only great diversity of living speciesBut the even greater diversity of extinct ones as wellThe common ancestor of living animalsMay have lived 1.2 billion–800 million years agoMay have resembled modern choanoflagellates, protists that are the closest living relatives of animalsFigure 32.3Single cellStalkWas probably itself a colonial, flagellated protistFigure 32.4Colonial protist,an aggregate ofidentical cellsHollow sphere of unspecialized cells (shown in cross section)Beginning of cell specialization Infolding Gastrula-like “protoanimal” Somatic cellsDigestivecavityReproductive cells(a)(b)Neoproterozoic Era (1 Billion–524 Million Years Ago)Early members of the animal fossil recordInclude the Ediacaran faunaFigure 32.5a, bPaleozoic Era (542–251 Million Years Ago)The Cambrian explosionMarks the earliest fossil appearance of many major groups of living animalsIs described by several current hypothesesFigure 32.6Mesozoic Era (251–65.5 Million Years Ago)During the Mesozoic eraDinosaurs were the dominant terrestrial vertebratesCoral reefs emerged, becoming important marine ecological niches for other organismsCenozoic Era (65.5 Million Years Ago to the Present)The beginning of this eraFollowed mass extinctions of both terrestrial and marine animalsModern mammal orders and insectsDiversified during the CenozoicConcept 32.3: Animals can be characterized by “body plans”One way in which zoologists categorize the diversity of animalsIs according to general features of morphology and developmentA group of animal speciesThat share the same level of organizational complexity is known as a gradeThe set of morphological and developmental traits that define a gradeAre generally integrated into a functional whole referred to as a body planSymmetryAnimals can be categorizedAccording to the symmetry of their bodies, or lack of itSome animals have radial symmetryLike in a flower potFigure 32.7aRadial symmetry. The parts of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images.(a)Some animals exhibit bilateral symmetryOr two-sided symmetryFigure 32.7bBilateral symmetry. A bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves.(b)Bilaterally symmetrical animals haveA dorsal (top) side and a ventral (bottom) sideA right and left sideAnterior (head) and posterior (tail) endsCephalization, the development of a headTissuesAnimal body plansAlso vary according to the organization of the animal’s tissuesTissuesAre collections of specialized cells isolated from other tissues by membranous layersAnimal embryos Form germ layers, embryonic tissues, including ectoderm, endoderm, and mesodermDiploblastic animalsHave two germ layersTriploblastic animalsHave three germ layersBody CavitiesIn triploblastic animalsA body cavity may be present or absentA true body cavityIs called a coelom and is derived from mesodermFigure 32.8aCoelomBody covering(from ectoderm)Digestive tract(from endoderm)Tissue layerlining coelomand suspendinginternal organs(from mesoderm)Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm.(a)A pseudocoelomIs a body cavity derived from the blastocoel, rather than from mesodermFigure 32.8bPseudocoelomMuscle layer(from mesoderm)Body covering(from ectoderm)Digestive tract(from ectoderm)Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.(b)Organisms without body cavitiesAre considered acoelomatesFigure 32.8cBody covering(from ectoderm)Tissue-filled region(from mesoderm)Digestive tract(from endoderm)Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall.(c)Protostome and Deuterostome DevelopmentBased on certain features seen in early developmentMany animals can be categorized as having one of two developmental modes: protostome development or deuterostome developmentCleavageIn protostome developmentCleavage is spiral and determinateIn deuterostome developmentCleavage is radial and indeterminateFigure 32.9aProtostome development(examples: molluscs, annelids,arthropods)Deuterostome development(examples: echinoderms,chordates)Eight-cell stageEight-cell stageSpiral and determinateRadial and indeterminate(a) Cleavage. In general, protostomedevelopment begins with spiral, determinate cleavage.Deuterostome development is characterized by radial, indeterminate cleavage.Coelom FormationIn protostome developmentThe splitting of the initially solid masses of mesoderm to form the coelomic cavity is called schizocoelous developmentIn deuterostome developmentFormation of the body cavity is described as enterocoelous developmentFigure 32.9bArchenteronBlastoporeMesodermCoelomBlastoporeMesodermSchizocoelous: solidmasses of mesodermsplit and form coelomEnterocoelous:folds of archenteronform coelomCoelom(b) Coelom formation. Coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development). Fate of the BlastoporeIn protostome developmentThe blastopore becomes the mouthIn deuterostome developmentThe blastopore becomes the anusFigure 32.9cAnusAnusMouthMouthMouth developsfrom blastoporeAnus developsfrom blastoporeDigestive tubeConcept 32.4: Leading hypotheses agree on major features of the animal phylogenetic treeZoologists currently recognize about 35 animal phylaThe current debate in animal systematicsHas led to the development of two phylogenetic hypotheses, but others exist as wellOne hypothesis of animal phylogeny based mainly on morphological and developmental comparisonsFigure 32.10PoriferaCnidariaCtenophoraPhoronidaEctoproctaBrachiopodaEchinodermataChordataPlatyhelminthesMolluscaAnnelidaArthropodaRotiferaNemerteaNematoda“Radiata”DeuterostomiaProtostomiaBilateriaEumetazoaMetazoaAncestral colonialflagellateOne hypothesis of animal phylogeny based mainly on molecular dataFigure 32.11CalcareaSilicareaCtenophoraCnidariaEchinodermataChordataBrachiopodaPhoronidaEctoproctaPlatyhelminthesNemerteaMolluscaAnnelidaRotiferaNematodaArthropoda“Radiata”“Porifera”DeuterostomiaLophotrochozoaEcdysozoaBilateriaEumetazoaMetazoaAncestral colonialflagellatePoints of AgreementAll animals share a common ancestorSponges are basal animalsEumetazoa is a clade of animals with true tissuesMost animal phyla belong to the clade BilateriaVertebrates and some other phyla belong to the clade DeuterostomiaDisagreement over the BilateriansThe morphology-based treeDivides the bilaterians into two clades: deuterostomes and protostomesIn contrast, several recent molecular studiesGenerally assign two sister taxa to the protostomes rather than one: the ecdysozoans and the lophotrochozoansEcdysozoans share a common characteristicThey shed their exoskeletons through a process called ecdysisFigure 32.12Lophotrochozoans share a common characteristicCalled the lophophore, a feeding structureOther phylaGo through a distinct larval stage called a trochophore larvaFigure 32.13a, bApical tuftof ciliaMouthAnus(a)An ectoproct, a lophophorate(b)Structure of trochophore larvaFuture Directions in Animal SystematicsPhylogenetic studies based on larger databasesWill likely provide further insights into animal evolutionary history