propagules and offspring

SPERM COMPETITION

Sperm competition - “the competition within a single female betweenthe sperm from two or more males for the fertilization of the ova.”

Prerequisites:

1. Multiple mating by females (before production of offspring)

2. Sperm storage

Multiple mating by females Parker, 1970

Polyandry

x

Lower probability of

sperm competition

Monogamy (or serial monogamy)

x Lays eggs

Very high probability of

sperm competition

Lays eggs

Does this apply to all types of reproducers?

Probably – as a consequence of spermcasting

Probably not

Why should a female mate multiple times?

1. Sperm replenishment

- ‘top up’ sperm supply

-Ridley (1988) – compared 48 species of insect

- 58% ran out of sperm if not re-mated- in all – remating increased fecundity

Mating frequency

Monandry Polyandry

Fecundity unchanged 6 - 7 1 - 2

Fecundity increased 1 36

Why should a female mate multiple times?

1. Sperm replenishment

2. Material benefits

-female acquires nutrients from ejaculate, spermatophore or prey

Why should a female mate multiple times?

1. Sperm replenishment

2. Material benefits

3. Genetic benefits

- gain sperm from ‘better’ male

- increase genetic diversity of offspring

Why should a female mate multiple times?

1. Sperm replenishment

2. Material benefits3. Genetic benefits

4. Convenience

Number of males acceped

Male densityLow High

2. Sperm Storage

Storage organs - spermatheca

Spermathecae of tarantulas

Sperm Storage

Duration

100 5001000 1500

Storage time in days

Several species of Mollusca

Male Strategies

What can males do to increase their chances of fertilization

1. Postcopulatory guarding

Male Strategies

What can males do to increase their chances of fertilization

2. Sperm removal

Male Strategies

What can males do to increase their chances of fertilization

3. Sperm packaging

Guerinna 2012

Gyrinidbeetles

Male Strategies

What can males do to increase their chances of fertilization

3. Sperm packaging

Apyrene vs eupyrene sperm

sterile fertile

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 development2) 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)

LIFE HISTORY TRAITS

Fecundity

- Total number of offspring (expressed as a number of offspring over a period of time)

Need to specify - unit counted (egg, larva etc)

- individual in which unit is counted (batch, female, colony)

- time scale

LIFE HISTORY TRAITS

Fecundity

- Total number of offspring (expressed as a number of offspring over a period of time)

Also closely associated with egg size

Fecundity x egg size = estimate of maternal investment

Egg Size and Quality

Main investment in egg – yolk

-protein, lipid and carbohydrate

ln Energy content and

ln Dry organic weight

Ln Egg volume

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

Life History Theory and Fecundity

Fitness - expected contribution of alleles, genotypes or phenotypes to next generation

Life history strategy – acquisition over time of a series of co-adapted traits

4 elements to life history evolution

1) Demographic parameters

2) Quantitative genetics

3) Trade offs between life history traits

4) Species specific design constriants

CENTRAL TO THIS – FECUNDITY – EXPENSIVE AND DIRECTLY LINKED TO FITNESS

ENVIRONMENTAL CONDITIONS

Habitat stability/predictability,Physical features

DEMOGRAPHIC FORCES

Age and size-specific traits

BIOTIC FACTORSSELECTIVE FORCES

OPTIMAL COMBINATION OF

TRAITS

EFFECT ON INDIVIDUAL FITNESS

EVOLUTION OF OPTIMAL LIFE HISTORY STRATEGY

GLOBAL EFFECT ON ORGANISM

GROWTHSURVIVAL

LONGEVITYFECUNDITY

PHYLOGENETIC, STRUCTURAL,FUNCTIONAL

CONSTRAINTS

Life History Theory and Fecundity

MODELS

1) Deterministic models : r and K selection

Parameters r-selectionK-selection

Environment variable/unpredictableconstant/predictablePopulation density independentdensity dependent

variable sizeconstant size

below Kat K

low competitionhigh competition

Life history traitsGrowth fast

slowDeath rate high

lowAdult size small

largeLifespan short

longAge at maturity early

delayedSpawning freq. semelparityiteroparityFecundity high

lowSize of offspring smalllargeJuvenile survivorship low

high

Life History Theory and Fecundity

MODELS

1) Deterministic models : r and K selection

Prediction:

Species with K-strategy will have a lower reproductive effort than r-species

Problems:1) No phylogenetic or morphological constraints

2) Based at the population level – ignores age-specific factors

Life History Theory and Fecundity

MODELS

2) Stochastic models

-predict similar combination of traits as r-K model but for different reasons

-based on uncertainty of

1) survival of zygote to maturity

2) survival of adult to reproduce

If environmental fluctuations variable juvenile mortality

delay maturity, low reproductive effort, small broodsIf adult mortality is high semelparity

Life History Theory and Fecundity

MODELS

3) Demographic model

Demography – analysis of effect of age structure on population dynamics

Uses age and size specific fecundity and mortality as basis of variation in fitness

Life History Theory and Fecundity

MODELS

4) Winemiller – Rose model

Fitness components

1) fecundity2) survivorship of juveniles3) age at maturity

Life History Theory and Fecundity

MODELS

4) Winemiller – Rose model

Fecundity

Age at maturity

Juvenile survivorship

OPPORTUNISTIC

PERIODIC

EQUILIBRIUM

Life History Theory and Fecundity

MODELS

4) Winemiller – Rose model

Life history traits OpportunisticEquilibrium Periodic

Adult size smalllarge large

Lifespan shortlong long

Age at maturity earlymoderate late

Spawning freq. multiple singlesingle

Fecundity /spawn lowlow highSize of offspring small large

smallJuvenile survivorship low

high low

Life History Theory and Fecundity

MODELS

4) Winemiller – Rose model

Periodic – like r except they are large, long lived and mature late

Opportunistic – like r except they have low fecundity

Equilibrium – like K strategists but with small – medium bodies

- maximize juvenile survivorship at expense of fecundity

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

Developmental Patterns-Kinds of eggs

• •• •

•••

••

••

••

••

••

••• •

Isolecithal

•

•

• •

••

•

•

••

••

••

•

••

••••

• •• ••

••

••

••

••

••• •

••••

•

Telolecithal

• •• •

•

••

•

••

•

••

••

•

••

•

••

•

••

••

••• • •• •••

• ••

••••

•

••

•

••

•

••

•

••

••

•

••

•

••

•

••

••

•

•

•

••• • •• ••

•• ••

•••

Cleavage through

entire egg

Cleavage not through

entire egg

Holoblastic

Meroblastic

Developmental Patterns-Kinds of eggs

Isolecithal - Holoblastic Telolecithal - Meroblastic

Developmental Patterns-Kinds of eggs

• •• •

•••

••

••

••

••

••

••• •

Isolecithal

•

•

• •

••

•

•

••

••

••

•

••

••••

• •• ••

••

••

••

••

••• •

••••

•

Telolecithal

• •• •

•

••

•

••

•

••

••

•

••

•

••

•

••

••

••• • •• ••

•• ••

•• •••

••

•

••

•

••

•

••

••

•

••

•

••

•

••

••

•

•

•

••• • •• ••

•• ••

•••

Holoblastic

Meroblastic

Planktotrophic larvae

Lecithotrophic larvae

1) Fertilization patterns

4) Settlement patterns

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

••

•

•

••

••

•

•

••

Dev.time

Egg size (mm) Egg size (mm)

••

•

•

•

•

•

•• •

••

•• ••

Nudibranchs Polychaetes

Planktotrophic

Lecithototrophic

Intraspecific comparisons

Larger larvae result in longer lifetimes

e. Ascidians and urchins

Dev.time

Egg size (mm)

Intraspecific comparisons

Increase can be dramatic

Conus

-4% increase in egg size

- 15% increase in development time

Intraspecific comparisons

Behavioural differences

Larger larvae spend more time in plankton

Choosier in settlement sites

Disperse more

Female should produce different size offspring – bet hedging

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

EVOLUTIONARY IMPLICATIONS

For species with planktonic larvae

juvenile

larva

gamete

Each has a different habitat-separated in time and space

EVOLUTIONARY IMPLICATIONS

For species with planktonic larvae

How does a female balance these?

e.g. female at high density

- Eggs are more likely to suffer polyspermy

-produce smaller eggs

-less dispersal

- More competition on settling

Sexual Selection in Broadcast Spawners

Females control range of sizes

Males control ultimate size of offspring(via control of sperm number & environment in which eggs are fertilized)

Potential for conflict

Female strategy – get all eggs fertilized

Male strategy – fertilize only the largest eggs

Next time – Dispersal and Settlement