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ZOOLOGY 300 > Week 2 > Flashcards

Week 2 Flashcards

1
Q

Who is the sister group of Metazoa?

A

Chanoflagellates

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2
Q

Describe Chanoflagellates

A
  • Chanoflagellatea is a group of eukaryotes
  • ~150 species
  • Unicellular
  • Heterotrophic
  • A single flagellum encompassed by a microvillar collar
  • Can form colonial aggregations
  • Sister group to the Metazoa
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3
Q

Chanoflagellate genome

A
  • Monosiga brevicollis: the first genome of a choanoflagellate
  • ~9,200 genes
  • Included in the genome are cell adhesion and cell signaling genes previously thought to be restricted to Metazoa
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4
Q

Phylum Porifera

A
  • Sponges
  • Simple, sessile animals that lack true tissues but have several totipotent cell types
  • Feeding occurs through specialized cells called choanocytes, which draw water through the sponge body and filter out particles
  • Particles ingested by phagocytosis or pinocytosis
  • Mostly filter feeders; some species carnivorous or boring
  • Mostly live in marine environments; some in freshwater
  • Skeleton supported by spicules, and often by an elastic network of fibers and an extracellular matrix with collagen
  • Reproduce sexually and asexually
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5
Q

Choanocytes

A

Specialized cells in sponges that draw water through the sponge body and filter out particles

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6
Q

Age of Largest Xestospongia muta specimens (sponge)

A

~2,300 years

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7
Q

Architecture of a Sponge

A
  • The body of a sponge is set up around its aquiferous system, a series of water current channels
  • The apical opening is called the osculum; the central cavity is the atrium
  • The outer wall is the pinacoderm, which is formed from cells called pinacocytes
  • Inner surface is choanoderm which is formed from cells called choanocytes
  • Between these thin cellular sheets is a matrix called the mesohyl
  • Small openings in the outer surface are called ostia
  • There is no basement membrane; the mesohyl (matrix) is just underneath the pinacocyte layer
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8
Q

Aquiferous system

A

The system of connected water channels that is unique to sponges

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9
Q

Osculum

A

Apical opening in sponge

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10
Q

Atrium

A

Central cavity in sponge

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11
Q

Pinacoderm

A

Outer wall of a sponge, formed from cells called pinacocytes

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12
Q

Choanoderm

A

Inner surface of sponge, formed from choanocytes

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13
Q

Mesohyl

A

Matrix within sponge

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14
Q

Ostia

A

Small openings in the outer surface of the sponge, formed by porocyte cells

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15
Q

Cells that line the surface of a sponge

A
  • Pinacocytes
  • Porocytes
  • Choanocytes
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16
Q

Pinacocytes

A

Flattened cells that line the exterior of the sponge body wall

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17
Q

Ameboid cells

A

These totipotent cells can travel freely through the mesohyl by ciliary movement

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18
Q

Porocytes

A

Cylindrical cells that form the ostia (the intake openings of the aquiferous systen)

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19
Q

Choanocyte cell

A

The feeding cells; Has a single flagellum and a microvillar collar. These make up the inner surface (choanoderm). Groups of choanocytes are clustered into choanocyte chambers which open into the aquiferous systems via incurrent and excurrent canals

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20
Q

Asconoid condition

A
  • Single osculum
  • Choanocytes line the choanoderm
  • Ostia opens directly into the atrium
21
Q

Simple synconoid condition

A
  • Analogous to a sponge built from multiple asconoids
  • Choanocyte chambers present
22
Q

Complex synconoid condition

A
  • Additional folding creates a denser mesohyl layer
  • Dermal pores now connected to prosopyles by incurrent canals
23
Q

Leuconoid condition

A
  • Additional folding and further thickening of the mesohyl
  • More numerous (but smaller) choanocyte chambers, often connected to each other in tandem
  • Multiple oscula in the apex
  • In many leuconoid sponges, there are 18,000 choanocyte chambers in one cubic millimeter of tissue
  • Each chamber pumps 1,200 times its volume daily
24
Q

Boring Sponges

A

Parasitic. Several groups of Demospongiae

25
Q

Carnivorous Sponges

A

Cladorhizidae (family of Demospongiae)

26
Q

Contractile Cells in Sponges

A

Myocytes; contractile cells that can open or shut parts of the aquiferous system

27
Q

Totipotent cells in Sponges

A

Archaeocytes; these enable reaggregation

28
Q

Cells in Sponges that secrete the skeleton

A
  1. Ameboid cells: collencytes, lophocytes, and spongocytes
  2. Sclerocytes: secrete spicules
29
Q

Role of Spicules

A

Reinforce the sponge skeleton

30
Q

Three groups that spicules are siliceous

A
  1. Class Hexactinellida
  2. Class Demospongiae
  3. Class Homoscleromorpha
31
Q

One group that spicules are calcitic

A

Class Calcarea

32
Q

Colonial Theory

A
  1. Invagination
  2. Ingression
33
Q

Molecular basis for colonial Theory

A
  • GKpid: The GK protein interaction domain
  • GKpid forms a complex with motor proteins which reinforces the direction of mitotic spindles (a key mechanism for generating pull forces at the cellular level)
  • GKpid is most closely related to the gene gk (guanylate kinase)
  • gk is common to all life and has a metabolic function: it catalizes the transfer of phosphate groups from ATP to GMP
  • Anderson et al. synthesized the ancestral sequences at two nodes – the intermediate ancestor (Anc-GK1pid) was able to catalyze production of ADP and orient mitotic spindle
  • The GKpid of a choanoflagellate can orient a mitotic spindle
  • gk and GKpid are largely similar in protein structure
  • Changing only a two amino acid sites in gkdup confer the ability to orient mitotic spindle
  • Interpretation: gk was duplicated and the duplicated copy (GKpid) underwent a mutation that conferred to ability to bind motor proteins. Therefore, this led to a gain of a protein complex that could orient mitotic spindles and produce sheets of cells
34
Q

Phylum

A

Defined as a group of species sharing a common ancestor and a unique assemblage of traits

35
Q

A bauplan

A

Body plan; The assemblage of traits and features that is shared by a phylum

36
Q

Phylogenetic trees represent what

A

Evolutionary history

37
Q

Taxa

A

Tips of phylogenetic tree. These are living organisms. All taxa that share a given common ancestor are equally evolved

38
Q

Clade/Monophyletic Group

A

Includes a common ancestor and all of its descendants

39
Q

A Grade/Paraphyletic Group

A

Includes a common ancestor and some of its descendants

40
Q

Polyphyletic Group

A

Includes some descendants of multiple common ancestors

41
Q

Challenge with phylogenetics

A

-Adding taxa to a tree increases the number of possible trees by a dramatic amount
- T= (2N-5)!!
- Finding an exact solution in parsimony analysis of phylogeny is NP-hard for trees with many taxa
- Heurisitc methods (employ a search strategy that is never guaranteed to find the optimal solution)

42
Q

What is the smallest number of characters we need to fully resolve a 4-taxon unrooted tree?

A

One.

43
Q

What is the smallest number of characters we need to fully resolve a 5-taxon unrooted tree?

A

Two…Needs one character for each internal
branch. For N taxa, I have (N – 3) internal branches.

44
Q

Molecular sequence data provides

A
  • an enormous source of phylogenetic characters
  • Both nucleotide and peptide sequences provide phylogenetic data
45
Q

homology

A

Character states that are shared by some taxa AND their common ancestors

46
Q

Homoplasy

A

Character states that are shared by some taxa, but NOT their common ancestors

47
Q

Some characters are “difficult” to gain

A
  • Gain of powered flight is rarely
    observed
  • losses of powered flight are
    frequently observed
48
Q

Weighted parsimony

A
  • if the costs of evolutionary events are different
  • Evolution is not always parsimonious because character state changes are not always equally probable (In DNA sequences, transition mutations are typically more common than transversion mutations (i.e., transitions have an intrinsically lower cost))
49
Q

Lord Howe Island

A

Tree Lobsters

ZOOLOGY 300 (5 decks)

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