propagules and offspring
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
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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
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Telolecithal
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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
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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)
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