dispersal of individuals in space: fruits, seeds (including size, endosperm, associations with...
TRANSCRIPT
Dispersal of individuals in space: Fruits, seeds (including size,
endosperm, associations with dispersers)
Questions
• Discussions: – Jon: posting paper and questions for this week– Eliot: will be picking a paper to post for week after
spring break
• Any questions?
Seeds and fruits
• What are they? What are they for?
FernsGymnosperms
Angiosperms
Evolution of seeds
• Early land plants: – Spores -> small gametophytes -> embryo ->
sporophyte– Fertilization dependent on motile sperm (like
ferns)
Evolution of seeds
• Seed plants: – Heterosporic (micro and mega) -> micro and
megagametophyte– Megaspore encased by sporangium when
germinates– Megagametophyte encased by integument
Evolution of seeds
• Lycopods came close but first were the pteridosperms
Seeds
• Gymnosperms: naked seed– Enclosed in woody or fleshy cone
• Angiosperms: enclosed seed– 1 or 2 cotyledons
• Why was enclosing gametophytes and seeds helpful?
Seeds
• Ripened ovule– Embryo: diploid– Endosperm: haploid or triploid nutritive tissue (oil,
starch, protein)– Seed coat: from integument– Appendages: arils, elaiosome, hair, wings
Fruits
• Fruits are ripened ovaries, seed-bearing part of the plant– Pericarp: ovary wall
• Epicarp: outer• Mesocarp: middle• Endocarp: inner
• Fruit morphology labile
Fruits
• Dehiscent:– Capsule: >2 carpels– Follicle: 1 carpel– Schizocarp: Fruit breaks into 1 carpel units
Fruits
• Indehiscent, dry:– Achene (variants include nuts)
• Indehiscent, fleshy:– Berry: seed(s) surrounded by fleshy pericarp– Drupe: seeds(s) surrounded by a stony endocarp
Fruit
• Simple: 1 or more carpels with one pistil• Aggregate: 1 flower with >1 pistil• Multiple: >1 flower
Fruits
• Facilitate dispersal:– Abiotic: explosive, wind, water
Fruits
• Facilitate dispersal:– Biotic:
• Hitch rides • Attract disperser via fruit• Attract disperser via seed• Attract disperser via appendages
Evolution of seed size
Ove Eriksson
Variation in seed size
Seed size: 1011
Evolution of seed size
Questions
• Why did larger seeds evolve? What is biotic dispersal related to larger seeds?
• Patterns over time:– Cretaceous (124 mya): small seeds (<1 mm3) and
little biotic dispersal– Early tertiary (65-38 mya): increase in seed size
mean and range and biotic dispersal– Late tertiary (38-2 mya): decrease in seed size mean
but not range (cooler climate and open vegetation)
Questions
• Why did larger seeds evolve? What is biotic dispersal related to larger seeds?
• Other patterns:– Biotic dispersal, typically larger seeds– Taller growth forms, typically larger seeds
Questions
• Why did larger seeds evolve? What is biotic dispersal related to larger seeds?
• Hypotheses– Coevolution? Diversification of mammals and birds ->
closed canopy vegetation– Recruitment? Change in climate and loss of large
herbivores -> closed canopy vegetation (light competition)
– Life form? Change to closed canopy forest -> larger and longer-lived plants, longer as juveniles
Evolution of seed size
Evolution of seed size
Evolution of seed size
Questions
• Why did larger seeds evolve? What is biotic dispersal related to larger seeds?
• Hypotheses– Coevolution? Maybe primates, ungulates, and
rodents not birds and bats. But why large seeds?– Recruitment? Environmental shifts compatible– Life form? Environmental shifts compatible
• Conclusions– Some of all three