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PROPAGULES AND OFFSPRING
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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
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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
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Patterns of Development
Nutritional mode
3) Osmotrophy
- Take DOM directly from sea water
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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
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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
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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)
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Developmental Patterns-Kinds of eggs
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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
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Developmental Patterns-Kinds of eggs
Isolecithal - Holoblastic Telolecithal - Meroblastic
1) Fertilization patterns
2) Development patterns
3) Dispersal patterns
4) Settlement patterns
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Developmental Patterns-Kinds of eggs
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Holoblastic
Meroblastic
Planktotrophic larvae
Lecithotrophic larvae
1) Fertilization patterns
2) Development patterns
3) Dispersal patterns
4) Settlement patterns
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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
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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
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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
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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
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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
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Effects of Offspring Size
2) Development
Prefeeding period increases with offspring size
Feeding period decreases with offspring size
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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
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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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Planktotrophic
Lecithototrophic
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Intraspecific comparisons
Larger larvae result in longer lifetimes
e. Ascidians and urchins
Dev.time
Egg size (mm)
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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
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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
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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
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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
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3) Among populations
a) habitat quality – poorer habitat results in smaller offspringb) latitudinal variation
Bouchard & Aiken 2012
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3) Among populations
a) habitat quality – poorer habitat results in smaller offspringb) latitudinal variation
Bouchard & Aiken 2012
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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
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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
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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
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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
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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
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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
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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