Campbell: Introduction To Animal Evolution

Front 1

What are the main defining features of an animal?

Back 1

nutrition, cell structure, tissues, life history, and Hox genes

Front 2

What is special about animal nutrition?

Back 2

Animals are multicellular eukaryotic chemoheterotrophs that ingest other organisms or organic material for energy.

Front 3

What is special about animal cells?

Back 3

They lack cell walls, and are instead held together by proteins like collagen, with intercellular junctions (tight junctions, desmosomes, and gap junctions) also held together by structural proteins.

Front 4

What is special about animal tissues?

Back 4

They have nervous and muscle tissue.

Front 5

What is special about animal life histories?

Back 5

Animals mainly reproduce sexually, with the diploid the dominant stage, with a small flagellated sperm fertilizing a stationary egg. After that, the zygote cleaves into a hollow 1-cell-thick bastula (sphere) of cells, after which gastrulation puts some of these cells on the inside. In addition, some animals have larval (sexually immature) stages before undergoing metamorphosis.

Front 6

What is a gastrula?

Back 6

A stage of eumetazoan life histories, it contains an outer cell layer called the ectoderm, an inner cell layer called the endoderm, with the blastocoel between ectoderm and endoderm, a body cavity inside the endoderm called the archenteron with a hole to the outside called the blastopore.

Front 7

What is special about animal genetics?

Back 7

Hox genes, only found in animals, are homeoboxes (gene-regulating genes) found in genes coding for body form development.

Front 8

Describe the ancestor of the animal kingdom.

Back 8

likely a colonial, flagellated protist closely related to choanoflagellates

Front 9

Is the animal kingdom monophyletic or paraphyletic?

Back 9

monophyletic

Front 10

How many animal phyla are there?

Back 10

35

Front 11

What are the two trees of animal life?

Back 11

The traditional tree is based on anatomy and embryology, while the newer tree is based on molecular systematics.

Front 12

What are grades in phylogeny?

Back 12

major branches that separate animals based on body plans

Front 13

What are the first two grades in the traditional phylogenetic tree of animals?

Back 13

Parazoa and Eumetazoa

Front 14

What distinguishes Parazoa from Eumetazoa?

Back 14

Parazoans (sponges) lack true tissues, while eumatazoans have them.

Front 15

What is the second set of grades in the traditional phylogenetic tree of animals?

Back 15

Radiata and Bilateria, in Eumetazoa

Front 16

What distinguishes Radiata from Bilateria?

Back 16

Radiata have radial symmetry (rotationally symmetric in one direction), while bilateria have dorsal (top), ventral (bottom), anterior (head) and posterior (tail) sides, as well as left and right.

Front 17

What is cephalization?

Back 17

an evolutionary trend in bilateria to concentrate sensory organs and often a central nervous system in the anterior end (the head)

Front 18

What are most radiata mobility-wise?

Back 18

sessile benthos or plankton

Front 19

What is different between the embryonic development of radiata and bilateria?

Back 19

Bilateria have a mesoderm, a third germ layer between ectoderm and endoderm that develops into muscles and other non-digestive organs, making them triploblastic, unlike radiata which are only diploblastic.

Front 20

What phyla are in Parazoa?

Back 20

just Porifera (sponges)

Front 21

What phyla are in Radiata?

Back 21

Cnidaria (jellies, corals, anemones) and Ctenophora (comb jellies)

Front 22

What is the third set of grades in the traditional phylogenetic tree of animals?

Back 22

Acoelomate, Pseudomoelomate, and Coelomate, within Bilateria

Front 23

What phyla are in Acoelomates?

Back 23

just Platyhelminthes (flatworms)

Front 24

What defines Acoelomates?

Back 24

They lack a cavity between the digestive tract and outer body wall, making their bodies solid.

Front 25

What distinguishes Pseudocoelomates from Coelomates?

Back 25

Coelomates have a true coelom, a body cavity completely lined with mesoderm-derived tissue, while pseudocoelomates have only part of their body cavity lined with mesoderm-derived tissue.

Front 26

What phyla are in Pseudocoelomates?

Back 26

Rotifera (rotifers) and Nematoda (nematodes)

Front 27

What functions can a body cavity have?

Back 27

cushion organs for protection, act as skeletons in forcing structure, and let organs and skin act independently

Front 28

What is the fourth set of grades in the traditional phylogenetic tree of animals?

Back 28

Protostomia and Deuterostomia, within Coelomates

Front 29

What phyla are in Protostomia?

Back 29

Mollusca (clams, snails, octopi), Annelida (segmented worms), and Arthropoda (crustaceans, insects, spiders)

Front 30

What phyla are in Deuterostomia?

Back 30

Echinodermata (sea stars, sea urchins) and Chordata (lancelets, tunicates, vertebrates)

Front 31

What distinguishes Protostomia and Deuterostomia?

Back 31

cleavage, coelom formation, and blastopore fate

Front 32

How does cleavage distinguish protostomes from deuterostomes?

Back 32

With exceptions, protostomes undergo spiral cleavage, in which smaller cells are put in the grooves between larger cells, and determinate cleavage, when every cell in early stages is vital to proper development. Meanwhile, deuterostomes undergo radial cleavage, in which the planes of cell division are parallel or perpendicular to an axis, and indeterminate cleavage, which means that each cell of small embryos has the ability to develop into a fully-formed individual, making identical twins and stem cells possible.

Front 33

How does coelom formation distinguish protostomes from deuterostomes?

Back 33

In the gastrula stage, protostomes show schizocoelous development, in which separate masses of mesoderm form the coelom, while deuterostomes show enterocoelous development, in which the coelom-forming mesoderm is initially attached to the archenteron.

Front 34

How does the fate of the blastopore distinguish protostomes from deuterostomes?

Back 34

The blastopore becomes the mouth of protostomes and the anus of deuterostomes, while another cavity forms to serve the other purpose.

Front 35

In general, how does molecular systematics establish phylogenies?

Back 35

It establishes clades, which are monophyletic divisions of organisms more closely related to each other than to anything else. It does this by looking for unique monomer sequences in genes and their products (polypeptides).

Front 36

What is the phylogenetic tree of animals based on?

Back 36

small subunit ribosomal RNA, supported by the Hox genes that have been sequenced

Front 37

What do the two phylogenetic trees of animals share?

Back 37

The deepest branches (Parazoa-Eumetazoa and Radiata-Bilateria) agree, and the deuterostome clade is monophyletic in both.

Front 38

What are the main ways the two phylogenetic trees differ?

Back 38

the existence of two main protostome clades, relocation of the acoelomates and pseudocoelomates into Protostomia, and assignment of the Lophophorate phyla.

Front 39

What are the two clades in Protostomia in the molecular systematics phylogenetic tree?

Back 39

Lophotrochozoa and Ecdysozoa

Front 40

Why are annelids more closely related to mollusks rather than arthropods in the molecular systematics phylogenetic tree?

Back 40

Besides the molecular data, both go through a trochophore larva stage.

Front 41

What animals are in Ecdysozoa?

Back 41

nematodes, arthropods, and any other protostomes that secrete exoskeletons, getting bigger and bigger (the shedding of old ones is called ecdysis)

Front 42

What are the lophophorate phyla?

Back 42

Bryozoa (bryozoans), Phoronida (phoronids), and Brachipoda (brachiopods)

Front 43

Where are the lophophorates phylogenetically?

Back 43

They share some characteristics with deuterostomes and protostomes, but molecular data indicates they are protostomes in Lophotrochozoa.

Front 44

Where does Lophotrochozoa get its name?

Back 44

by sticking the lophophorates and trochophore larva together

Front 45

When did the animal phyla arise?

Back 45

between 565 and 525 million years ago, in the late Precambrian and early Cambrian

Front 46

What is the period before the Cambrian?

Back 46

the Ediacaran period, named for the Ediacara Hills in Australia

Front 47

What evidences suggest a date much earlier than the Cambrian for the diversification of animals?

Back 47

Paleontologists have found what could be burrows of animals in rock that's 1.1 billion years old, and molecular systematics agrees.

Front 48

What animal forms are found in Ediacaran rock?

Back 48

animals similar to cnidarians or hydras, soft-bellied mollusks, and burrows and tracks made by worms

Front 49

What is the Cambrian explosion?

Back 49

the sudden appearance of nearly all major animal body plans in Cambrian rocks between 543 and 525 million years ago

Front 50

Where has the Cambrian explosion been documented?

Back 50

Burgess Shale, British Columbia; Greenland and Yunnan, China which are more than 10 million years earlier

Front 51

Are the fossils found in Cambrian rock more often classified as extinct or extant?

Back 51

extant

Front 52

What are the three main hypotheses for why the Cambrian explosion happened?

Back 52

ecological, geologic, or genetic causes

Front 53

How could ecological causes have resulted in the Cambrian explosion?

Back 53

Predator-prey relationships developed, leading to greater selective pressures and diversification.

Front 54

How could geological causes have resulted in the Cambrian explosion?

Back 54

Atmospheric concentration of oxygen (for example) reached a high enough level to support active metabolism by animals.

Front 55

How could genetic causes have resulted in the Cambrian explosion?

Back 55

Hox genes allowed the diversity in morphology at the embryonic level (evo-devo).

Front 56

What does molecular data have to say about the Cambrian explosion?

Back 56

Since the lophotrochozoans, ecdysozoans, and deuterostomes each have difficult-to-resolve molecular relationships (they all branched out at once), the Cambrian explosion was really three explosions, one for each of those clades.

Front 57

Did any additional phylum-level animal evolution go on after the Cambrian explosion?

Back 57

No, but changes did occur within phyla.