Plant Reproductive BiologyMichael G. Simpson
What is it?
Study of sexual and asexual reproduction
Pollination mechanisms
Gene flow
Genetic variation
Propagule dispersal
Why study it?
Insight into adaptive significance & homology of systematic characters
Insight into delimitation of species and subspecies.
Sexual Reproduction
Non-seed plants
Seed plants:
Pollination - transfer of pollen from microsporangia to stigma (angiosperms) or ovule (gymnosperms)
Wind pollination - ancestral (all gymnosperms)
Animal pollination - derived for angiosperms
Some angiosperms secondarily wind pollinated
Fertilization - fusion of sperm and egg ––> embryo (new sporophyte)
Strategy of animal pollination:Attractant & Reward
Attractant
Visual
perianth
stamens (e.g., Myrtaceae, Mimosoideae)
staminodes (e.g., Zingiberaceae, Cannaceae)
corona (e.g., Narcissus)
inflorescence
Olfactory - usu. from perianth
sweet
rotten (foul/fetid) - e.g., fly pollinated flowers
Strategy of animal pollination:Attractant & Reward
Reward
Nectar
Pollen
Waxes
Resins
or “Trick” instead of a “Treat”Insect trapped (Aristolochia) or drowned (Nymphaea sp.)
Mimicry
E.g., fooling male insect into “mating” with orchid
Pollination Mechanisms
INSECT (entomophily)
Bees (melittophily/hymenopterophyly):
fls. showy, colorful, fragrant, with:
nectar guides
landing platforms
Butterflies (psychophily):
fls showy, colorful, fragrant
no nectar guides
long tubes or spurs
Pollination Mechanisms
Moths (phalaenophily):
large, white, fragrant
no nectar guides
usually tubes or spurs
Pollination Mechanisms
Flies (sapromyiophily)
maroon / brown in color
foul smelling (like rotting flesh)
Pollination Mechanisms
Birds (ornithophily):
red (often, not always)
tubular (often)
Pollination Mechanisms
Bats (cheiropterophily):
nocturnal anthesis
large, colorful or white
produce copious nectar or pollen
Pollination Mechanisms
Wind (anemophily):
flowers small, numerous, often unisexual
perianth absent or non-showy
flowers often produced in mass
Pollination Mechanisms
Water (hydrophily):
Breeding systems
Outbreeding versus Inbreeding vs. in-between
Breeding systems
Outbreeding = outcrossing / allogamy / xenogamy:
How is it promoted?
1) Plant sex: dioecy (incl. gynodioecy, androdioecy, trioecy)
Breeding systemsOutbreeding = outcrossing / allogamy / xenogamy:
2) Difference in timing of floral parts = dichogamy
protandry - male first
protogyny - female first
Breeding systemsOutbreeding = outcrossing / allogamy / xenogamy:
3) Spatial separation of anthers and stigmas = hercogamy
heterostyly: different style/stigma & correlated anther heights
enantiostyly: left & right-handed flowers
Outbreeding = outcrossing / allogamy / xenogamy:
3) Spatial separation of anthers and stigmas = hercogamy
movement hercogamy: trigger mechanisms
Outbreeding = outcrossing / allogamy / xenogamy:
3) Spatial separation of anthers and stigmas = hercogamy
movement hercogamy: e.g., stigma movement
Diplacus [Mimulus] aurantiacus (Phyrmaceae)
Outbreeding = outcrossing / allogamy / xenogamy:
3) Spatial separation of anthers and stigmas = hercogamy
Folding of style best explained as adaptation to reduce interference in bird pollination
Outbreeding = outcrossing / allogamy / xenogamy:
4) Self-incompatibility
Genetically determined, inability for fertilization to occur between gametes derived from one individual.
Inbreeding = selfing
autogamy (w/in 1 flower) & geitonogamy (between fls. of 1 indiv.)
Selective advantage: ensures propagule production
Disadvantage: reduced to absent genetic variability
allautogamy: both outcrossing & inbreeding
e.g., Viola, Clarkia: two flower types:
chasmogamous flowers - normal, open
cleistogamous flowers - remain closed
Fruit/seed dispersal
Wind - samaras, winged seeds
Water - e. g., Cocos nucifera (Arecaceae)
Explosive dehiscence
Self (Autochory, e. g., Arachis hypogaea)
Animal
Asexual Reproduction
Vegetative reproduction: ramets
Rhizomes
Bulbs, bulbels
Corms, cormels
Plantlets
Asexual Reproduction
Agamospermy - seed production without fertilization
Parthenogenesis (diploid egg)
Adventive polyembryony (non-egg diploid cell)
Hybridization in plants
Polyploidy – evolution of multiple sets of chromosomes; major mechanism of speciation.
Hybridization in plants
Common
Can produce sterile, vegetatively reproducing species (e. g., certain cacti)
Testing for breeding mechanisms
A B C D
1) Control + + + +
2) Caged, self-pollinated - + + +
3) Caged, left alone - - + +
4) Emasculated, caged - - - +
5) Caged, emascul., outcrossed + + + +
What is the breeding mechanisms for species A, B, C, D?
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