Bio 103 Lake Tahoe Community College
Winter Quarter Instructor: Sue Kloss
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Chapter 32: Animal Evolution and Diversity
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How many animal species? From 10 – 30 million, and as many as 100 – 200 million.
I. What makes an animal an animal?
A. These features, taken together, distinguish animals from other life
1. Eukaryotic: this feature unites them with all eukaryotes (plants, animals, fungi, and protists, and separates them from archaea and bacteria (prokaryotes)
a. Lack cell walls, distinguishes animals from plants, algae and fungi which have at least partial cell walls
2. Multicellular: separates animals from protists, generally unicellular; most plants, animals and fungi are multicellular.
a. Cells are specialized and held together by structural protein collagen
b. two cell types not found in other euks – nerves and muscles
3. Heterotrophic: separates them from plants and algae (plantlike protists), Psing; groups them with fungi -they ingest food
4. Reproduction and Development
B. Other features
1. Most animals take food into their bodies for nutrition, they generally have a digestive tract 2. Unique junctions between cells
3. Life cycles
a. except for haploid sperm and egg, all life stages of animals are diploid
b. male and female adults make haploid germ cells (gametes) by meiosis
c. egg and sperm fuse – zygote
d. early mitotic divisions – blastula (embryonic stage)
e. One side of blastula folds inward to form another embryonic stage – gastrula. (Fig. 32.2)
1). Gastrula now has an outer cell layer and an inner cell layer from infolding
2). inner layer becomes digestive system
3). outer layer becomes epidermis and nervous system
4). in most animals, a third layer forms between other 2 layers and becomes most other internal organs
5). many animals develop from gastrula into adults
6). some animals, like sea star, develop into 1 or more larval stages (intermediates).
a. A larva is an immature individual that looks very different from adult, and
doesn’t have capacity for sexual reproduction, may eat difft. food
7). Larvae undergo major change of body form, called metamorphosis, to become adults capable of sexual reproduction
4. Despite extraordinary animal diversity, underlying genetic network that controls animal development
has been well conserved
a. all euks have genes that control expression of other genes,
b. many regulatory genes of animals have common sequences of DNA in called homeobox , or
hox genes
c. since all animals share these hox genes, it suggests that all animals derive from a common
ancestor
d. hox genes play important roles in the deveopment of animal embryos, controlling the
expression of dozens or even hundreds of other genes
e. hox genes therefore control cell differentiation, producing lots of morphological features
of animals
C. Animal history may span more than a billion years
1. Molecular clocks suggest animals may have diverged from fungi 1.5 billion yrs ago
a. 99% of all animal species that have ever lived my be extinct
b.
2. Speculation about 1st animal
a. colonial protists - cells divide but don’t separate; colonies may have been hundreds or thousands of cells
b. hollow sphere, possibly. Floating aggregates of cells that ingested organic nutrients from the waters. (Fig. 32.3)
c. division of labor - locomotion, digestion, reproduction; at some point, division of labor- somatic vs. reproductive
d. still a long way from highly specialized, interdependent nature of true multicellularity; hollow colony must become layered
e. infolding may have produced a hollow colony for specialized feeding and digestive cells
f. infolding may have eventually eliminated hollow portion, paving way for more layers of cell, division of labor.(Fig. 32.4)
g. perhaps by this time, junctions may have formed btn cells for distributing nutrients and holding cells together
h. organism with this level of organization could be called primitive animal, or protoanimal (organism that gave rise to animals)
i. probably a crawler, not a floater, perhaps ate nutrients off ocean floor
D. Neoproterozoic Era - 1 bya to 542 mya
1. Oldest known fossil animals- 575 mya - Ediacaran fauna - in Ediacaran hills of Australia
2. theory from molecular data (clocks) suggests a much earlier origin, but no fossil evidence of it yet
E. Paleozoic Era - 542-251 mya
1. Most modern animal phyla fossils from the Cambrian explosion, 542-525 mya
2. many have distinctive fossils - include first animals with hard mineralized skeletons, and look
quite different from most modern animals (fig. 32.6)
a. why then? 3 hypotheses
1. new predator prey relationships generated a bunch of diversity
2. O2 in atmosphere allowed more dynamic metabolism
3. evolution of gene complexes provided developmental flexibility for more variation
3. Animal diversity continued to increase during Ordovician, Silurian and Devonian periods, punctuated
by mass extinctions
4. Vertebrates (fishes) became top predators of marine food webs, and by 460 mya, arthropods started
making it to land - millipedes and centipedes in fossil record
5. vertebrates made it to land 360 mya and diversified (amphibians, reptiles and mammals) F. Mesozoic Era - 251 - 65.5 mya
1. animal phyla from the Paleozoic spread to new niches
2. first coral reefs formed, reptiles went back to marine niches and succeeded as large aquatic
predators
3. wings appeared, and flying reptiles and birds
4. large dinos appeared as both predators and herbivores
5. first mammals - tiny nocturnal insect eaters
G. Cenozoic Era- 65.5 mya - present
1. Insects and flowering plants - huge diversication, following mass extinctions of terrestrial and marine
animals, inc. large dinos and marine reptiles
2. rise of large mammals into herbivore and predator roles
3. global climate gradually cooled, triggering significan shifts in many animal lineages
a. african primates moved from dense forests to open woodlands and savannas
II. Animals can be characterized by body plans
A. body plans - a set of morphological and developmental traits that integrate into a functional whole
1. symmetry (fig. 32.7) - suits an animals life style
a. lack of (sponges)
b. radiates - parts that radiate out from a center (jellies)
c. bilateraterians - 2 sided symmetry
1. dorsal
2. ventral
3. anterior
4. posterior
5. cephalization
2. Tissues - layering occurs in gastrulation - 2 layers - diploblastic; 3 layers - triploblastic
a. Ectoderm - covering and in some animals, nervous system
b. Endoderm - innermost layer - developing digestive tube, or archenteron, gives rise
to digestive system and other organs
c. Mesoderm - muscles and most other organs
d. all bilaterally symmetric animals are triploblasts
3. Body Cavities - fluid filled space separating digestive tract from outer body wall
a. also called a coelom - true coeloms formed from mesoderm
1. mesenteries form sheets of tissue that connect organs in suspension in cavity
b. pseudocoeloms form from blastocoel, not mesoderm, but are really functional coeloms
despite the name
c. some triploblasts lack cavities, they are acoelomates
d. functions of body cavities
1. fluids can act as hydrostatic skeleton inside a cavity (earthworm)
2. organs can grow and move independently of body wall
3. cushions and prevents injury, allows dynamic movement
4. Protostome and Deuterostome (Fig. 32.9)
a. protostomes - blastopore becomes mouth
1. spiral cleavage
2. determinate cleavage
3. splits in mesoderm form coelom
b. deuterostome
1. radial cleavage
2. coelom formation occurs by outgrowth of mesoderm from archenteron
3. indeterminate cleavage
III. Major Animal Features
A. Intro
1. Currently recognize 35 animal phyla
2. science is a dynamic process of inquiry - new methods produce new information and reorg of “the
known”
3. Used to use morphological traits, now we use molecular sequencing - causes disparities (32.10,11)
B. Points of agreement
1. all animals share a common ancestor
2. sponges diverged from other animals, then tissues evolved - so are classed as parazoa
3. all other animals are “eumetazoans” - true animals. Common ancestor of eumetazoans acquired
true tissues
4. Most animals are bilaterians - Cambrian explosion was diversification of this group
5. Vertebrates and some other phyla are deuterostomes (disagreement about which groups)
Ch. 32 OBJECTIVES1. / List the five characteristics that combine to define animals.
2. / Describe the role of Hox genes in animal development.
3. / Describe the evidence that suggests animals may have first evolved about a billion years ago.
4. / Explain the significance of the Cambrian explosion. Describe three hypotheses for the cause of the Cambrian explosion.
5. / Outline the major groups of the animal kingdom based on symmetry, embryonic germ layers, the presence or
absence and type of coelom, and protostome or deuterostome development.
6. / Distinguish between radial and bilateral symmetry. Explain how animal symmetry may match the animal’s way of life.
7. / Distinguish among the acoelomate, pseudocoelomate, and coelomate grades. Explain the functions of a body cavity.
8. / Distinguish between the following pairs of terms:
a. diploblastic and triploblastic
b. spiral and radial cleavage
c. determinate and indeterminate cleavage
d. schizocoelous and enterocoelous development
9. / Compare the developmental differences between protostomes and deuterostomes, including:
a. pattern of cleavage
b. fate of the blastopore
c. coelom formation
8. / Name five major features of animal phylogeny that are supported by systematic analyses of morphological characters and recent molecular studies.