AP Biology, Chapter 32
Introduction to Animal Evolution

SUMMARY
INTRODUCTION

WHAT IS AN ANIMAL?
	Introduction
		1. List the characteristics that define animals and distinguish them from other organisms.
			a. Ingestion followed by digestion
			b. Cells lack cell walls
				i. Cells held together by molecules including collagen
				ii. Cells connected by tight junctions, desmosomes, gap junctions
			c. Most have nervous and muscular tissue (not Porifera)
			d. Characteristic developmental stages
				i. Sperm + egg  zygote
				ii. Mitosis = cleavage  blastula, a fluid-filled ball
				iii. Infolding/streaming produces gastrula with germ layers
				iv. Site of infolding = blastopore
				v. Further growth yields sexually immature larva
				vi. Further growth/metamorphosis yields sexually mature adult

AN OVERVIEW OF ANIMAL PHYLOGENY AND DIVERSITY
	Introduction
		2. Explain how and when the first animals likely evolved.
			a. Animal kingdom is a clade
			b. From a colonial flagellated protist >700 mya
			c. Hollow spherical colony infolded and specialized		
		3. Describe the nature of the scientific evidence that is reshaping our view of the 
		phylogenetic relationships of all forms of life. Explain how this revolution illustrates the 
		scientific process.
			a. rRNA sequences [clades below are ***ed]
			b. New technology allows new tests of older models
		4. Outline the major phylogenetic branches of the animal kingdom based on grades of 
		organization; symmetry and embryonic germ layers; the absence or presence of a body 
		cavity; and the protostome-deuterostome dichotomy. Distinguish between radial and 
		bilateral symmetry.
	Parazoans lack true tissues
			a. Parazoa*** ("beside the animals)
				i. One phylum, Porifera, the sponges
				ii. No tissues, except maybe epidermis
				iii. No muscle or nervous tissue
			b. Eumetazoa*** ("true animals")
				i. Jellies, worms, slugs, bugs, stars, and rats
				ii. Tissues
	Radiata and bilateria are the major branches of eumetazoans
			a. Symmetry
				i. Irregular shape, no matching parts = asymmetry
				ii. Cylindrical, matching halves around an axis = radial
					.Radiata*** includes Cnidaria*** and Ctenophora***
					.Top and bottom but no left or right
				iii. Right, left, dorsal, ventral, anterior, posterior = bilateral
					.Bilateria *** includes worms, slugs, bugs, stars, rats
					.Specialized anterior end = cephalization
					.Concentrated sense organs on exploring/feeding end
			b. Germ layers
				i. Gastrulation gives inner endoderm, outer ectoderm
				ii. Mesoderm forms between the two
				iii. Fates
					.Endo- lines the gut and respiratory organs
					.Ecto- forms the skin and nervous system
					.Meso- forms connective and muscular tissues
				iv. Warning: organs are combinations of these 
	Evolution of body cavities led to more complex animals
		5. Distinguish among the acoelomate, pseudocoelomate, and coelomate grades.
			a. This characteristic does not define animal clades
			b. Types
				i. Acoelomates lack space between germ layers; flatworms
				ii. Peudocoelomates have space between endo- and meso-; roundworms
				iii. Coelomates have a cavity lined with mesoderm
			c. Uses
				i. Allows space for more complex organs
				ii. Hydraulics
				iii. Allows mesoderm to specialize for digestion and locomotion
	Coelomates branched into protostomes and deuterostomes
		6. Distinguish between spiral and radial cleavage; determinant and indeterminate 
		cleavage; schizocoelous and enterocoelous development; and, blastopore fate.
			a. Cleavage geometry
				i. Spiral: mitotic spindles at diagonals to embryo axis; protostomes***
				ii. Radial: spindles parallel and perpendicular; deuterostomes***
			b. Cell fates
				i. Determinant: cells fixed on a developmental pathway; protostomes***
				ii. Indeterminant: cells can adjust; deuterostomes***
			c. Formation of coelom
				i. Schizocoelous: solid mesoderm splits; protostomes***
				ii. Enterocoelous: mesoderm buds from endoderm; deuterostomes***
			d. Blastopore fate
				i. Becomes the mouth; literally, "first mouth"; protostomes***
				ii. Becomes the anus; deuterostomes***
		7. Compare the developmental differences between protostomes and deuterostomes, 
		including: patterns of cleavage, fates of the blastopore, coelom formation.
			a. Protostomia***: spiral, determinate, schizocoelous, mouth
			b. Deuterostomia***: radial, indeterminate, enterocoelous, anus
		8. Compare the phylogenetic tree based on grades in body plans with the emerging view 
		of animal phylogeny based mainly on molecular biology.
			a. Body cavity has been cut as a dividing characteristic
			b. Protostomes have been reorganized
				i. Lophotrochozoa***
					.Most of the worms, mollusks, and rotifers
					.Share anatomical and developmental homology
				ii. Ecdysozoa***
					.Nematoda*** and Arthropoda***
					.Grow by molting after forming a new outer covering

THE ORIGINS OF ANIMAL DIVERSITY
	Most animal phyla originated in a relatively brief span of geological time
		9. Describe the evidence that suggests animals may have first evolved about a billion 
		years ago.
			a. Fossil burrows, 1.1 billion years old
		10. Describe the nature of the Ediacaran fossils.
			a. Cnidarians, mollusks, worms
			b. Many burrows and tracks 
		11. Explain the significance of the Cambrian explosion. Describe the nature of its fossil 
		organisms.
			a. Nearly all of current body plans appeared 545-525 mya
			b. Corresponds to appearance of hard parts
	Developmental genetics may clarify our understanding of the Cambrian 
	diversification
		12. Explain and compare the three main hypotheses for what caused the Cambrian 
		diversification of animals.
			a. Emergence of predator-prey relationships  new shells and locomotion
			b. Critical oxygen concentration  more active metabolism
			c. Developmental regulatory genes with homeobox

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