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Animal Origins and Basal Lineages Flashcards

1
Q

Animals arose from

A

Opisthokont protists

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2
Q

Molecular analysis reveals that choanoflagellate are the

A

sister group of animals

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3
Q

What are the closest living relatives of animals?

A

Choanoflagellates

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4
Q

Choanoflagellates and animals both possess genes found in no other organisms

A

cadherins (cell-cell adhesion proteins), tyrosine kinase receptors, Myc (growth transcription factor), SOX (stemness transcription factor), p53
(tumor suppressor)

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5
Q

Choanoflagellates and early-stage animal embryos both have

A

multicellular spherical developmental stages that are homologous (derived from MRCA)

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6
Q

Choanocytes bear a striking resemblance to

A

choanoflagellates

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7
Q

Choanocytes are similar to choanoflagellates because:

A
  1. posses a flagellum
  2. capture their prey using a collar
  3. phagocytose their prey and digest it intracellularly
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8
Q

Similarities between choanocytes and choanoflagellates are

A

homologies and reveal shared ancestry of animals and choanoflagellates

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9
Q

The earliest animal fossils are from the

A

late proterozoic (600-650 MYA)

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10
Q

The first animals were likely ______ much like choanoflagellate sisters

A

spherical multicellular clusters

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11
Q

How was the metazoan phylogenetic tree determined?

A

Using molecular analysis/phylogenetics (compare sequences across different species)

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12
Q

What was compared to determine which animals were closely related in molecular phylogenetic of Metazoans?

A

SSU (small subunit) rRNA gene sequence

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13
Q

What does the SSU rRNA gene encode?

A

ribosomal RNA (SSU rRNA or 18S rRNA) that forms part of the small subunit of the ribosome

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14
Q

Why is ribosomal RNA important?

A

It is critical for translation and cell viability

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15
Q

Ribosomal RNA accumulates

A

mutations infrequently as it is important for cell survival

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16
Q

Why was the SSU rRNA gene chosen for molecular analysis?

A

When doing molecular analysis of distantly related lineages (like animal phyla) it is helpful to use a gene that changes slowly

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17
Q

What is the clade Metazoa?

A

“Higher animals” or Animal Kingdom

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18
Q

Each lineage on the Metazoan tree is at ____ level

A

phylum

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19
Q

How did multicellularity arise in the animal MRCA?

A
  1. Unique intercellular scaffold proteins such as collagen
  2. Unique intercellular connections such as tight junctions and gap junctions
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20
Q

What are the 2 synapomorphies of metazoans?

A
  1. multicellularity
  2. two germ layers in the embryo
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21
Q

In all animals, zygotes undergo mitosis to form a

A

blastula

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22
Q

What is a blastula?

A

A single layer of cells that form a hollow sphere

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23
Q

Gastrulation is when:

A

Cells fold inwards to create an inner cavity called the
archenteron

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24
Q

The blastula undergoes a process called _____ to form a _____

A

gastrulation, gastrula

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25
The gastrula has distinct layers of ________
undifferentiated cells (stem cells) called germ layers
26
What do the germ layers in gastrula do?
Give rise to different tissues and organs
27
What are the two germ layers of the gastrula of all metazoans?
ectoderm and endoderm
28
What is the ectoderm?
outer cell layer; gives rise to the skin and nervous system
29
What is the endoderm?
inner cell layer that lines the archenteron; gives rise to the digestive tract
30
Which evolved a third germ layer?
Ctenophores and bilateralians
31
What is the third germ layer?
the mesoderm: middle cell layer between ectoderm and endoderm which gives rise to: 1. skeletal 2. muscular 3. connective tissues and internal organs
32
What is the most basal animal lineage?
Ctenophora phylum/ the comb jellies
33
Ctenophores possess bands of cilia used for
locomotion (ex: comb jellies using for movement)
34
What are the 3 synapomorphies of the phylum ctenophora/"comb bearing"?
1. bands of cilia 2. mesoderm (third germ layer) 3. a complex nervous system
35
Bilateral animals also having a mesoderm and complex nervous systems are an example of:
convergent evolution
36
How do phylum Ctenophora reproduce?
Most reproduce sexually and most are hermaphroditic: individuals possess male and female gonads
37
Sponges are the phylum
porifera
38
The MRCA of sponges loses what through evolutionary reversal?
the second germ layer
39
What does the loss of the second germ layer make sponges?
morphologically primitive
40
Because sponges are morphologically primitive, the Phylum Porifera have no:
a) No true tissues b) no organs c) no symmetry
41
In the phylum porifera, the single germ layer gives rise to
specialized cells w/ different functions (sponges have specialized cells with different functions)
42
Sponges are sessile, which means they
adhere to a substrate and stay put
43
What do sponges use to bring in bacteria and plankton for food?
Sponges use choanocytes (specialized cells) to create a water current by beating their flagella, which pulls in bacteria and plankton.
44
How do phylum Porifera reproduce?
Reproduce sexually but many are hermaphroditic (like Cnetophora)
45
Choanocytes bear a striking resemble to _____, evidence of shared ancestry
choanoflagellates
46
Choanocytes have these similar features to choanoflagellates:
1. flagellum 2. capture prey using a collar 3. phagocytose their prey and digest it intracellularly
47
The phylum Cnidaria composed of: (3)
1. jellies 2. anemones 3. corals
48
What is the synapomorphy of the phylum cnidaria? (think jellies, anemones, corals)
stinging cells called cnidocytes which all cnidarians posses
49
Cnidaria posses ___ embryonic germ layers
2
50
What do the 2 germ layers give rise to in cnidarians?
true tissues (muscle and nervous tissue) but NO true organs
51
Phylum Cnidaria have no
true organs (no heart, lungs, kidneys)
52
What are the synapomorphies of the clade bilateria? (2)
1. gain of mesoderm 2. bilateral symmetry
53
Radial symmetry:
can be cut along any point of its central axis to produce symmetrical halves
54
Radial symmetry arises independently in
ctenophorans, cnidarians, and echinoderms
55
Bilateral symmetry:
can only be cut along the anteroposterior (head to tail) axis to produce symmetrical halves (two true halves) Arose in bilateral MRCA but not present in all bilaterians
56
Sponges lack symmetry due to
loss of the second germ layer
57
What is the Cambrian Explosion?
~ 541 MYA animals began a period of extensive and rapid diversification/speciation
58
How many years after rise of first animals was Cambrian explosion?
~60 million years after (541 MYA)
59
The Cambrian explosion lasted for _____ years
~25 million years
60
Most bilateral animal phyla present today appeared during the
Cambrian Explosion
61
Chordates (bilateral animal phyla) appeared during the Cambrian explosion and is the phylum that later gave rise to
vertebrates
62
The development of more complex body plans in animals seen during the early Cambrian would have required
an increase in the amount of cellular ATP (energy) in these animals
63
The animals would have required more ____ for cellular respiration to make ______
oxygen, ATP
64
Cambrian explosion coincides with an increase in
atmospheric oxygen (which would have allowed for rapid evolution to occur)
65
HYP 1: Rapid Speciation during Cambrian Explosion
The evolution of predators began an evolutionary arms race between predators and prey which catalyzed their evolution
66
What is an evolutionary arms race?
Characterized by escalating adaptations and counter-adaptations in predators and prey (e.g., cheetahs and gazelles)
67
HYP 2: Rapid Speciation during Cambrian Explosion
The evolution of Hox gene clusters in bilateral animals catalyzed the evolution of new body plans
68
Hox genes encode
Hox proteins
69
What are Hox proteins?
transcription factors which turn on other genes that control body patterning along the anteroposterior (head to tail) axis
70
What are transcription factors?
Proteins that bind the regulatory sequences of genes to control their expression
71
How are Hox proteins expressed during development?
Expressed in specific segments along the anteroposterior axis and turn on genes that determine what body parts form in those segments
72
The greater the # of Hox genes,
the more complex the body pattern
73
Hox gene clusters are well conserved in bilateral animals suggesting
they arose early in the evolution of this clade
74
Molecular studies suggest that Hox genes first arose in
pre-Cambrian animals
75
During the Cambrian explosion, the duplication of Hox genes gives rise to
Hox gene clusters (quickly giving rise to new body plans)
76
As Hox gene clusters evolved, so did
new body plans (more Hox genes, more complex body plans)

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