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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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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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