LIFE HISTORY PATTERNS. Spawning and Fertilization.
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Transcript of LIFE HISTORY PATTERNS. Spawning and Fertilization.
LIFE HISTORY PATTERNS
Spawning and
Fertilization
Evolution of Anisogamy
Imagine some Precambrian creature
Produces undifferentiated gametes
Fertilization
G. Parker
Gametes produced come in a variety of sizes
Large Medium Small
Number produced
Mitotic competence
Gamete size
Number produced
Size distribution of gametes produced
External fertilization
Which ones are the most likely to produce offspring?
Combinations
Competence Frequency of contact
Very high Very high Very high
Moderate Low
Very low
Very low Moderate Very high
Low High
Very high
Gamete size
Number produced
After several generations
Selected against
Anisogamy
FERTILIZATION
TYPES OF SPERM AND EGG RELEASE AND FERTILIZATION
1. Broadcast spawners (= free spawners)
-eggs and sperm are released into the water column - fertilization is external
2. Spermcast spawners
-sperm are released into the water column and taken in by the female-fertilization is internal
3. Copulators
-sperm placed in the body of the female usually with some intromittent orgtan-fertilization is internal
SPAWNING
1. BROADCAST SPAWNING
SPAWNING
1. BROADCAST SPAWNING
Problems for broadcast spawners
How does an animal ensure fertilization by dumping eggs and sperm in the open ocean?
1. Proximity
2. Timing
3. Currents
4. Sperm/egg contact
Boradcast spawners suffer a dilution effect
Quinn and Ackerman. 2011. Limnol Oceanogr. 2011: 176
1. Proximity
How to get around this problem
mussels oysters
2. Timing and synchrony
How to get around this problem
Haliotis asinina
Counihan et al. 2001. Mar.Ecol.Prog.Ser.213:193
2. Timing and synchrony
How to get around this problem
Haliotis asinina
Counihan et al. 2001. Mar.Ecol.Prog.Ser.213:193
2. Timing and synchrony
How to get around this problem
Haliotis asinina
Counihan et al. 2001. Mar.Ecol.Prog.Ser.213:193
2. Timing and synchrony
How to get around this problem
Haliotis asinina
Counihan et al. 2001. Mar.Ecol.Prog.Ser.213:193
2. Timing and synchrony
How to get around this problem
Haliotis asinina
Counihan et al. 2001. Mar.Ecol.Prog.Ser.213:193
Conclusions (Counihan et al. 2001)
1. Spawning season is determined by water temperature
2. Precise time of spawning is influenced by tidal regime
3. Both sexes spawn in response to an evening high tide
4. Males spawn 19 mins before high tide: females 11 mins after
5. More animals spawn in presence of opposite sex.
3. Currents
3. Currents
Patterns of flow – move gametes unpredictably
Advection – mean direction and velocity of a gamete cloud
Diffusion –rate of gamete spreading
Main problem – production of eddies (vortices) – unpredictable and ephemeral
3. Currents
4. Sperm-egg contact
a. Dilution
-is it sperm concentration or egg:sperm ratio?
If sperm and egg are at similar concentrations-sperm :egg ratio is important
Sperm:egg ratio importantSperm concentration
is imporant
Final problem
Egg and sperm longevity
Sperm live less than a few hours
Horseshoe crabsSea urchins
Sea starsAscidianshydroids
Eggs live about 3x longer than spermSea urchins
Sea starsAscidians
How can sperm and egg increase the chances of contact?
a) Chemical attractants
How can sperm and egg increase the chances of contact?
a) Chemical attractants
L- Tryptophan in abalone
Tryptophan ‘cloud’
How can sperm and egg increase the chances of contact?
b) Jelly coat
Jelly coat increases the size of the egg and acts as a sperm‘trap’
Fertilization
Spermcast spawning
-mating “by releasing unpackaged spermatozoa to be dispersed to conspecifics where they fertilize eggs that have been retained by their originator.”
Bishop and Pemberton.2006. Integr.Comp.Biol. 46:398
Fertilization
Spermcast spawning
In most spermcasters -
Sperm release
Intake by female
Storage of sperm
Fertilization and brooding
Release of competent larvae
Fertilization
Spermcast spawning
Factors influencing spermcasters
2. Conservation of energy
Sperm release
Sperm are inactive or periodically active
Intake by ‘female’
Sperm consistently activeConsequence: Fertilization can happen with fewer sperm at greater distance
Fertilization
Spermcast spawning
Factors influencing spermcasters
3. Sperm storage
-allows accumulation of a number of allosperm
Celleporella hyalina - Several weeks Diplosoma listerianum - 7 weeks
Fertilization
Spermcast spawning
Factors influencing spermcasters
4. Egg development
Celleporella hyalina
Diplosoma listerianum
Sperm release
Intake by ‘female’
Triggering of vitellogenesis
Consequence: Investment in eggs is not wasted.
PROPAGULES AND OFFSPRING
Patterns of Development
Nutritional mode
1) Planktotrophy
- larval stage feeds
This separates marine invertebrates from all others – can feed in dispersing medium
- Probably most primitive
Patterns of Development
Nutritional mode
2) Maternally derived nutrition
a) Lecithotrophy - yolk
b) Adelphophagy – feed on eggs or siblings
c) Translocation – nutrient directly from parent
Patterns of Development
Nutritional mode
3) Osmotrophy
- Take DOM directly from sea water
Patterns of Development
Nutritional mode
4) Autotrophy
- by larvae or photosynthetic symbionts
- In corals, C14 taken up by planulae
- In Porites, symbiotic algae to egg
Patterns of Development
Site of Development
1) Planktonic development
- Demersal – close to seafloor
- Planktonic – in water column
2) Benthic development
- Aparental – independent of parent – encapsulation of embryo
- Parental – brooding – can be internal or external
Patterns of Development
Dispersal Potential of Larvae
1) Teleplanic
- Larval period – 2 months to 1 year +
3) Anchioplanic- larval period – hours to a few days
2) Achaeoplanic – coastal larvae-1 week to < 2 months
(70% of littoral species)
Developmental Patterns-Kinds of eggs
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Telolecithal
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Cleavage through
entire egg
Cleavage not through
entire egg
Holoblastic
Meroblastic
1) Fertilization patterns
2) Development patterns
3) Dispersal patterns
4) Settlement patterns
Developmental Patterns-Kinds of eggs
Isolecithal - Holoblastic Telolecithal - Meroblastic
1) Fertilization patterns
2) Development patterns
3) Dispersal patterns
4) Settlement patterns
Developmental Patterns-Kinds of eggs
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Telolecithal
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Holoblastic
Meroblastic
Planktotrophic larvae
Lecithotrophic larvae
1) Fertilization patterns
2) Development patterns
3) Dispersal patterns
4) Settlement patterns
LIFE HISTORY TRAITS
Fecundity
- Total number of offspring (expressed as a number of offspring over a period of time)
Three categories of fecundity
1) Potential – number of oocytes in ovary
2) Realized – number of eggs produced
3) Actual – number of hatched larvae
CENTRAL TO THIS – FECUNDITY – EXPENSIVE AND DIRECTLY LINKED TO FITNESS
Relationship of fecundity to other traits
1) Egg size- Generally egg size 1/fecundity
Look at poeciliogonous species
Streblospio benedicti
Produce both lecithotrophic andplanktotrophic larvae
Lecithotrophic – egg 6X larger
Planktotrophic –6X as many eggs
Same reproductive investment
OFFSPRING SIZE
-volume of a propagule once it has become independent of maternal nutrition
Egg size – most important attribute in:
1) Reproductive energetics
2) Patterns of development and larval biology
3) Dispersal potential
Effects of Offspring Size
1) Fertilization
-some controversy about evolution of egg size
Either a) influenced by prezygotic selection for fertilization
OR
b) post-zygotic selection
Effects of Offspring Size
1) Fertilization
One consequence of size-dependent fertilization
Low sperm concentration larger zygotes High sperm concentration smaller zygotes (effects of polyspermy)
Size distribution of zygotes - function of both maternal investment and of local sperm concentration
Effects of Offspring Size
2) Development
Prefeeding period increases with offspring size
Feeding period decreases with offspring size
Effects of Offspring Size
2) Development
Prefeeding period increases with offspring size
Feeding period decreases with offspring size
Evidence?
Planktotrophs
1) pre-feeding period -larger eggs take longer to hatch
in copepods
- in nudibranchs – no effect
2) Entire planktonic period
-review of 50+ echinoids – feeding5 echinoids – non feeding
Larval period decreases with increase in egg size
But for polychaetes and nudibranchs
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Dev.time
Egg size (mm) Egg size (mm)
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Nudibranchs Polychaetes
Planktotrophic
Lecithototrophic
Intraspecific comparisons
Larger larvae result in longer lifetimes
e. Ascidians and urchins
Dev.time
Egg size (mm)
POST -METAMORPHOSIS
Does egg size affect juvenile size?
EchinoidsNudibranchsConus
a.Planktotrophs
Size at metamorphosis is independent of egg size
b. Non-feeding larvae
H. erythrogramma
-used for post-metamorphic survival
-most maternal investment (lipid)-not necessary for larval development
POST -METAMORPHOSIS
Does egg size affect juvenile size?
b. Non-feeding larvae
Bugula
-larval size affects - post settlement mortality- growth-
reproduction-offspring
quality-need energy to develop feeding structures – 10 – 60% of reserves
Summary of Offspring Size
Predictions
-closer to metabolic minimum
1) Species with non-feeding larvae-greatest effect is on post-metamorphic survival
2) Sources of mortality - physical, disturbance, stress – size independent- biological sources – size dependent
3) Offspring size- very different effects among populations
SOURCES OF VARIATION IN OFFSPRING SIZE
1) Offspring size varies
a) within broodsb) among mothersc) among populatioins
2) Within populations
a) stress – salinity, temperature, food availability, pollutionb) maternal size - +ve correlation
3) Among populations
a) habitat quality – poorer habitat results in smaller offspringb) latitudinal variation
Bouchard & Aiken 2012
3) Among populations
a) habitat quality – poorer habitat results in smaller offspringb) latitudinal variation
Bouchard & Aiken 2012
OFFSPRING SIZE MODELS
Same basic features
1) Trade off in size and number of offspring
2) Offspring size-fitness function
1) Trade off in size and number of offspring
N =c/S c = resourcesN = numberS = Size
Refers to energetic costs to mother not energy content of eggs
Size:energy content more variable
OFFSPRING SIZE MODELS
Same basic features
1) Trade off in size and number of offspring
2) Offspring size-fitness function
1) Trade off in size and number of offspring
-other costs may be involved
e.g. packaging of embryos
e.g. brood capacity of the mother
OFFSPRING SIZE MODELS
Same basic features
1) Trade off in size and number of offspring
2) Offspring size-fitness function
2) Offspring size-fitness function
- Focused on planktonic survival
Decrease in size
Longer planktonic period
Higher mortality
OFFSPRING SIZE MODELS
Same basic features
1) Trade off in size and number of offspring
2) Offspring size-fitness function
2) Offspring size-fitness function
Other effects - fertilization rates- facultative feeding- generation time- post metamorphic effects
VARIATION IN OFFSPRING SIZE AFFECTS EVERY LIFE HISTORY STAGE
VARIATION IN OFFSPRING SIZE AFFECTS EVERY LIFE HISTORY STAGE
SUMMARY OF EFFECTS
Planktotrophs
- Strong effects of offspring size on life history stages
1) Fertilization in free (broadcast) spawners
2) Larger eggs result in larvae that spend less time in the plankton
3) Larger larvae feed better
VARIATION IN OFFSPRING SIZE AFFECTS EVERY LIFE HISTORY STAGE
SUMMARY OF EFFECTS
2. Non-feeders
- Strong effects of offspring size on life history stages
1) Fertilization success
2) Developmental time
3) Maximize larval lifespan
4) Postmetamorphic performance
5) Subsequent reproduction and offspring size
VARIATION IN OFFSPRING SIZE AFFECTS EVERY LIFE HISTORY STAGE
SUMMARY OF EFFECTS
3. Direct developers
- Strongest effects of offspring size on life history stages
- Mothers may be able to adjust provisioning to local conditions