SPERM COMPETITION
Sperm competition - “the competition within a single female between
the 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
Monogamy (or serial monogamy)
x
Lays eggs
Lower
probability of
sperm
competition
Polyandry
x
Lays eggs
Very high
probability of
sperm
competition
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 benefits
3. Genetic benefits
4. Convenience
Number of
males
acceped
Low
High
Male density
2. Sperm Storage
Storage organs - spermatheca
Spermathecae of tarantulas
Sperm Storage
Duration
Several species of Mollusca
100
500
Storage time in days
1000
1500
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
Gyrinid
beetles
Guerinna 2012
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 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
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
Life history strategy – acquisition over time of a series of co-adapted traits
Fitness - expected contribution of alleles, genotypes or phenotypes to next generation
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
SELECTIVE FORCES
BIOTIC FACTORS
GLOBAL EFFECT ON
ORGANISM
GROWTH
SURVIVAL
LONGEVITY
FECUNDITY
EFFECT ON
INDIVIDUAL FITNESS
OPTIMAL
COMBINATION OF
TRAITS
EVOLUTION OF OPTIMAL
LIFE HISTORY STRATEGY
PHYLOGENETIC,
STRUCTURAL,
FUNCTIONAL
CONSTRAINTS
Life History Theory and Fecundity
MODELS
1) Deterministic models : r and K selection
Parameters
r-selection
K-selection
Environment
variable/unpredictable
constant/predictable
Population
density independent
variable size
below K
low competition
density dependent
constant size
at K
high competition
fast
high
small
short
early
semelparity
high
small
low
slow
low
large
long
Life history traits
Growth
Death rate
Adult size
Lifespan
Age at maturity
Spawning freq.
Fecundity
Size of offspring
Juvenile survivorship
delayed
iteroparity
low
large
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 broods
If 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) fecundity
2) survivorship of juveniles
3) age at maturity
Life History Theory and Fecundity
MODELS
4) Winemiller – Rose model
Fecundity
PERIODIC
OPPORTUNISTIC
Age at maturity
EQUILIBRIUM
Juvenile survivorship
Life History Theory and Fecundity
MODELS
4) Winemiller – Rose model
Life history traits
Adult size
Lifespan
Age at maturity
Spawning freq.
Fecundity
/spawn
Size of offspring
Juvenile survivorship
Opportunistic
Equilibrium
Periodic
small
short
early
multiple
low
small
low
large
long
large
long
moderate
single
low
large
high
late
single
high
small
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
Produce both lecithotrophic and
planktotrophic larvae
Lecithotrophic – egg 6X larger
Planktotrophic –6X as many eggs
Same reproductive investment
Streblospio benedicti
Developmental Patterns
-Kinds of eggs
Holoblastic
Isolecithal
•
• •
•
• •
•
•
•
• • •
•
•
•• •
•• • •
Cleavage through
entire egg
•
•
••
••
•
•• • •• ••
• • •• • •
••
••
• •• •• •• •
•
•
• • • •
•
•
Telolecithal
Meroblastic
••••••••••••••• ••
•
••
•• •••••••••••••• ••
•
••••
••
••••••• •••••••••
•• •• •
•
•
•
•
•
Cleavage not through
entire egg
•
•
•
•
•
Developmental Patterns
-Kinds of eggs
Isolecithal - Holoblastic
Telolecithal - Meroblastic
1) Fertilization patterns
Developmental Patterns
-Kinds of eggs
Holoblastic
Isolecithal
•
• •
•
• •
•
•
•
• •
•
••
•• •
4) Settlement patterns
•
•
•
•
•
•
••
••
•
•• • •• ••
• • •• • •
••
••
• •• •• •• •
•
•
• • • •
•
•
Planktotrophic larvae
Telolecithal
••••••••••••••• ••
•
••
•• •••••••••••••• ••
•
•
•
•
•
•
Meroblastic
••••
••
••••••• •••••••••
•• •• •
•
• •
• •
Lecithotrophic larvae
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
•
•
•
•
•
•
•
•
•
•
Planktotrophic
•
•
•
Dev.
time
Polychaetes
•
•
Egg size (mm)
••
•
•
•
Lecithototrophic
•
• •
• •
Egg size (mm)
•
•
•
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?
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
EVOLUTIONARY IMPLICATIONS
For species with planktonic larvae
gamete
larva
juvenile
Each has a different habitat
-separated in time and space
EVOLUTIONARY IMPLICATIONS
For species with planktonic larvae
e.g. female at high density
- Eggs are more likely to
suffer polyspermy
-produce smaller eggs
-less dispersal
- More competition on
settling
How does a female balance these?
Sexual Selection in Broadcast Spawners
Males control ultimate size of offspring
(via control of sperm number & environment in which eggs are fertilized)
Potential for conflict
Females control range of sizes
Female strategy – get all eggs fertilized
Male strategy – fertilize only the largest eggs
Next time – Dispersal and Settlement