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 +
2) Achaeoplanic – coastal larvae
-1 week to < 2 months
(70% of littoral species)
3) Anchioplanic
- larval period – hours to a few days
1) Fertilization patterns
2) Development patterns
3) Dispersal patterns
Developmental Patterns
-Kinds of eggs
4) Settlement patterns
Holoblastic
Isolecithal
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Cleavage through
entire egg
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Telolecithal
Meroblastic
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Cleavage not through
entire egg
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Developmental Patterns
-Kinds of eggs
Isolecithal - Holoblastic
1) Fertilization patterns
2) Development patterns
3) Dispersal patterns
4) Settlement patterns
Telolecithal - Meroblastic
1) Fertilization patterns
2) Development patterns
3) Dispersal patterns
Developmental Patterns
-Kinds of eggs
Holoblastic
Isolecithal
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4) Settlement patterns
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Planktotrophic larvae
Telolecithal
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Lecithotrophic larvae
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
Produce both lecithotrophic and
planktotrophic larvae
Lecithotrophic – egg 6X larger
Planktotrophic –6X as many eggs
Same reproductive investment
Streblospio benedicti
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 – feeding
5 echinoids – non feeding
Larval period decreases with increase in egg size
But for polychaetes and nudibranchs
Nudibranchs
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Planktotrophic
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Dev.
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Polychaetes
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Lecithototrophic
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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?
a.Planktotrophs
Echinoids
Nudibranchs
Conus
Size at metamorphosis is
independent of egg size
b. Non-feeding larvae
H. erythrogramma
-most maternal investment (lipid)
-not necessary for larval development
-used for post-metamorphic survival
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
1) Species with non-feeding larvae
-greatest effect is on post-metamorphic survival
-closer to metabolic minimum
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 broods
b) among mothers
c) among populatioins
2) Within populations
a) stress – salinity, temperature, food availability, pollution
b) maternal size - +ve correlation
3) Among populations
a) habitat quality – poorer habitat results in smaller offspring
b) latitudinal variation
Bouchard & Aiken 2012
3) Among populations
a) habitat quality – poorer habitat results in smaller offspring
b) 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 = resources
N = number
S = 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