lecture 19: external fertilization Flashcards

1
Q

how to efficiently broadcast spawn?

A

increase number to increase success

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2
Q

examples of organisms that do this

A

echinoderms
- urchins
- sea stars

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3
Q

why is broadcast spawning good?

A

inexpensive
- not a lot of energy used to make internal or external anatomy
- lots of gametes
- no reproductive organs in males

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4
Q

risks of external fertilization

A

high risk of wasted gametes

gamete dilution

non-synchrony

***experiment showed high success of gametes when released right over urchin

current speeds and distance impacted success of fertilization

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5
Q

strategies to minimize gamete waste

A

1) reproductive aggregations

2) synchronized release of gametes

3) sperm attractants

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6
Q

spawning cues for Great Barrier Reef corals

A

1) increased seawater temp or increasing photoperiod

2) lunar cue
- wait till calmer water so less water movement

3) light-off cue –> spawn only after sunset

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7
Q

sperm attractants

A

VERY specific

even between closely related species

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8
Q

acrosome reaction

A

acrosome reaction happens when sperm finds egg

1) sperm makes contact w jellycoat of an egg

2) exocytosis of acrosomal vesicle
- the acrosomal membrane breaks down

3) acrosomal enzymes digest the jellycoat

4) actin polymerization
- subacrosomal granule
is induced to polymerize
- turns acrosomal vesicle
inside out
- the dotted part now outside
– receptors on the vitelline envelope bind bindin

***if bindin doesnt bind, no fertilization

***bindin only binds to conspecific vitelline envelope of species specifics —> conspecifics

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9
Q

bindin

A

bindin only binds to conspecific vitelline envelope of species specifics —> conspecifics

  • gamete recognition protein of sea urchins
  • exposed on acrosomal process by acrosome reaction
  • bindin receptors on vitelline envelope of the egg
  • facilitate conspecific gamete binding
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10
Q

what is polyspermy and how to stop it

A
  • simultaneous fusion of two or more sperm
  • Both sperms introduce a centriole and nucleus to egg
  • Results in cleavage abnormalities – fatal for egg

HOW IS IT PREVENTED:
- fast block
- slow block

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11
Q

How is polyspermy prevented?

A
  • Fast block – egg membrane depolarization

– as soon as bindin binds to vitelline envelope - a wave of depolarization goes thru - any sperm coming up behind, sperm cannot bind in state of depolarization - this wave doesnt last v long - like miliseconds —> so slow block then necessary

  • Slow block – cortical granule exocytosis
  • ‘harden’ vitelline envelope preventing entry of additional sperm
    – vitelline envelope undergoes exocytosis reaction —> where lots of crosslinks happen w glyoprotein —> gets larger and hard —> then next sperm that start to swim up reach this hard barrier
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12
Q

For broadcast spawning organisms, reproductive failure has different causes at different male densities:

A

Low density males –> excessive sperm dilution

High density males –>
polyspermy

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13
Q

Different alleles of bindin gene can have subtle effects:

A
  • enhance fertilization success at LOW sperm density
  • enhance fertilization success at HIGH sperm density by minimizing polyspermy
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14
Q

change in selection pressure on urchins bc of otters

A
  • Shift in allele frequencies of bindin over last 200+ years
  • Animals conceived 200 years ago have higher LD frequency (low population density at time of fertilization)
  • Animals conceived recently have higher HD frequency (high population density at time of fertilization)
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15
Q

spermcast mating

A
  • males broadcast spawn sperm
  • females sequester the sperm to fertilize retained eggs
    – common in sessile marine inverts
  • suspension feeders will filter food and collect sperm this way
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16
Q

Can spermcast mating counteract sperm dilution threshold?

A

need atleast 100,000 sperm
in 1 mL of water for broadcast

spermcasting way less for
successful fertilization

17
Q

internal fertilization (and tactics by organisms)

A

sperm directly deposited into reproductive tract of female

  • expensive systems but abt 100% success rate
    – need whole reproductive systems - energetically costly

Unequal investment between the two sexes = sexual selection
- females want best male, not just any

EXAMPLE:
- European green crab
* Copulation window – female ecdysis
* Mate guarding
- hold her for perfect moulting timing
* Pheromonal control
* Offspring release

18
Q

What is uridine diphosphate?
Any significance to moulting?

A

uridine diphosphate is a pheromone

incredibly important to moulting process
- as closer to moulting process, more UDP is produced

19
Q

organisms that mate guard

A

European green crabs

tidepool copepod

***both from detection of pheromone