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PROPAGULES AND OFFSPRING

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.

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PROPAGULES AND OFFSPRING

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  1. PROPAGULES AND OFFSPRING

  2. 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

  3. 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

  4. Patterns of Development Nutritional mode 3) Osmotrophy - Take DOM directly from sea water

  5. 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

  6. Patterns of Development Site of Development 1) Planktonic development - Demersal – close to seafloor - Planktonic – in water column 2) Benthic development 2) Benthic development - Aparental – independent of parent – encapsulation of embryo - Parental – brooding – can be internal or external

  7. 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

  8. 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

  9. 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

  10. Egg Size and Quality Main investment in egg – yolk -protein, lipid and carbohydrate ln Energy content and ln Dry organic weight Ln Egg volume

  11. 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

  12. Life History Theory and Fecundity Life history strategy – acquisition over time of a series of co-adapted traits Fitness - expected contribution of allele, genotype or phenotype 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

  13. ENVIRONMENTAL CONDITIONS Habitat stability/predictability, Physical features DEMOGRAPHIC FORCES Age and size-specific traits SELECTIVE FORCES BIOTIC FACTORS GROWTH SURVIVAL LONGEVITY FECUNDITY GLOBAL EFFECT ON ORGANISM EFFECT ON INDIVIDUAL FITNESS PHYLOGENETIC, STRUCTURAL, FUNCTIONAL CONSTRAINTS OPTIMAL COMBINATION OF TRAITS EVOLUTION OF OPTIMAL LIFE HISTORY STRATEGY

  14. Life History Theory and Fecundity MODELS 1) Deterministic models : r and K selection Parameters r-selection K-selection Environment variable/unpredictableconstant/predictable Population density independentdensity dependent variable sizeconstant size below Kat K low competitionhigh competition Life history traits Growth fastslow Death rate highlow Adult size smalllarge Lifespan shortlong Age at maturity earlydelayed Spawning freq. semelparityiteroparity Fecundity highlow Size of offspring smalllarge Juvenile survivorship lowhigh

  15. 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

  16. 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

  17. 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

  18. Life History Theory and Fecundity MODELS 4) Winemiller – Rose model Fitness components 1) fecundity 2) survivorship of juveniles 3) age at maturity

  19. Life History Theory and Fecundity MODELS 4) Winemiller – Rose model Fecundity PERIODIC OPPORTUNISTIC Age at maturity EQUILIBRIUM Juvenile survivorship

  20. Life History Theory and Fecundity MODELS 4) Winemiller – Rose model Life history traits OpportunisticEquilibriumPeriodic Adult size smalllarge large Lifespan shortlong long Age at maturity earlymoderate late Spawning freq. multiple single single Fecundity /spawn lowlow high Size of offspring smalllarge small Juvenile survivorship lowhigh low

  21. 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

  22. Relationship of fecundity to other traits • 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 Streblospiobenedicti Same reproductive investment

  23. 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

  24. 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

  25. 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

  26. Effects of Offspring Size 2) Development Prefeeding period increases with offspring size Feeding period decreases with offspring size

  27. Effects of Offspring Size 2) Development Prefeeding period increases with offspring size Feeding period decreases with offspring size Evidence? Planktotrophs • pre-feeding period • -larger eggs take longer to hatch • in copepods • - in nudibranchs – no effect

  28. 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 Polychaetes Planktotrophic • • • Lecithototrophic • Dev. time • • • • • • • • • • • • • • • • • • • • • • • • Egg size (mm) Egg size (mm)

  29. Intraspecific comparisons Larger larvae result in longer lifetimes e. Ascidians and urchins Dev. time Egg size (mm)

  30. Intraspecific comparisons Increase can be dramatic Conus -4% increase in egg size - 15% increase in development time

  31. 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

  32. 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

  33. 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

  34. Summary of Offspring Size Predictions • 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

  35. 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

  36. 3) Among populations a) habitat quality – poorer habitat results in smaller offspring b) latitudinal variation Bouchard & Aiken 2012

  37. 3) Among populations a) habitat quality – poorer habitat results in smaller offspring b) latitudinal variation Bouchard & Aiken 2012

  38. 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 c = resources N = number S = Size N =c/S Refers to energetic costs to mother not energy content of eggs Size:energy content more variable

  39. 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

  40. 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

  41. 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

  42. 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

  43. 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

  44. 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

  45. EVOLUTIONARY IMPLICATIONS For species with planktonic larvae gamete Each has a different habitat -separated in time and space larva juvenile

  46. EVOLUTIONARY IMPLICATIONS For species with planktonic larvae e.g. female at high density - Eggs are more likely to suffer polyspermy -produce smaller eggs How does a female balance these? -less dispersal - More competition on settling

  47. 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

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