dispersal of individuals in space: fruits, seeds (including size, endosperm, associations with...

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