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


Haliotis asinina

Counihan et al. 2001. Mar.Ecol.Prog.Ser.213:193



Haliotis asinina




Haliotis asinina




Haliotis asinina




Haliotis asinina


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


a) Chemical attractants

L- Tryptophan in abalone

Tryptophan ‘cloud’


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


3. Sperm storage

-allows accumulation of a number of allosperm

Celleporella hyalina - Several weeks Diplosoma listerianum - 7 weeks

Fertilization

Spermcast spawning


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


Nutritional mode

2) Maternally derived nutrition

a) Lecithotrophy - yolk

b) Adelphophagy – feed on eggs or siblings

c) Translocation – nutrient directly from parent


Nutritional mode

3) Osmotrophy

- Take DOM directly from sea water


Nutritional mode

4) Autotrophy

- by larvae or photosynthetic symbionts

- In corals, C14 taken up by planulae

- In Porites, symbiotic algae to egg


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


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


Isolecithal - Holoblastic Telolecithal - Meroblastic






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Holoblastic

Meroblastic

Planktotrophic larvae

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

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


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


2) Development

Prefeeding period increases with offspring size

Feeding period decreases with 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


N =c/S c = resourcesN = numberS = Size

Refers to energetic costs to mother not energy content of eggs

Size:energy content more variable


Same basic features




-other costs may be involved

e.g. packaging of embryos

e.g. brood capacity of the mother


Same basic features




- Focused on planktonic survival

Decrease in size

Longer planktonic period

Higher mortality


Same basic features




Other effects - fertilization rates- facultative feeding- generation time- post metamorphic effects

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


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


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

Documents

LIFE HISTORY PATTERNS. Spawning and Fertilization