Reproductive Biology of Trees

Pollination

Wind-pollination Syndrome

• Morphology

– Small, insignificant flowers

– Lack nectar, bright colors & odor

– Pollen production>>>ovule production

– Spatial separation of stamens and pistils

– Flowers open before leaf production

• Common in Temperate; infreq. in

tropics

• Why?– Good long distance dispersal

– Few tree species—easy to find mate

– Fewer pollinating insects

Wind-pollination Syndrome

• Morphology

– Small, insignificant flowers

– Lack nectar, bright colors & odor

– Pollen production>>>ovule

production

– Spatial separation of stamens and

pistils

– Flowers open before leaf

production

• Common in Temperate; infreq.

In tropics

• Why?– Good long distance dispersal

– Few tree species—easy to find mate

– Fewer pollinating insects

Wind-pollination Syndrome

• Monoecy—separate staminate

and pistillate flowers on same

plant

– Frequent on wind-pollinated trees

– Quercus, Fagus, Juglans, Carya,

Betula, Corylus, Carpinus, Ostrya

– Special cases:

• Andromonoecy-perfect and

staminate flowers on same plant

• Gynomonoecy

Add photo of Quercus

Wind-pollination Syndrome

• Dioecy—separate staminate and pistillate

flowers on same plant

– Wind-pollinated taxa include Salix, Populus,

Fraxinus, some Acer, and Ginkgo

– Special cases

• Androdioecy—plants with staminate flowers and

other plants with hermaphroditic flowers

• Gynodioecy

female

male

Tropical vs Temperate

Tree Pollination

• Tropical

– Specialized flowers

– Animal pollinated

– Low density

populations

– Phenology divergence

– Dioecy common

• Temperate

– Generalized flowers

– Wind pollinated

– Dominant tree species

– Phenology similar

– Monoecy and

hermaphroditism

common

Animal Pollination Syndrome

• Morphology– Large, colorful flowers

– Nectar guides, tactile, olfactory, visual

– High quality pollination

– Mechanical & biochemical mechanisms of encouraging outcrossing

– Temperate examples: Catalpa, Liriodendron, Aesculus, Robinia, Tilia (often members of abundant tropical families)

– 95% of tropical trees—bats, birds, insects

– Insects in temperate zone

Cercis

Prunus

Magnolia

Tilia

Robinia

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Polygamomonoecy in Aesculus

Plant with male, female,

and hermaphroditic flowers

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Abundance of Staminate Flowers

increase overall attractiveness of floral display

increase reproductive output by siring more seeds on other plants

Pistillate flowers positioned basally to

be close to carbohydrate resources for seed development

increase outcrossing by matching natural movement of pollinators.

Insect Pollination

of Catalpa & Kalmia

Specialized pollination

—insects of specific size and mass required

Insect Pollination

of Sambucus & Viburnum, Cornus

Generalize flowers that attract beetles, flies, bees, and butterflies.

Soil pollinators with pollen.

Viburnum lantanoides

Large sterile flowers on

outside of floral display

Unusual Sex Expression

in Striped Maple • Sex Expression in Acer pensylvanicum

– 4% monoecious; 96% dioecious

– Male to female; 1:8

– 10% of trees change sex and usually to

female

– Female trees appear less vigorous and

have high mortality

• As understory tree, striped maples

on verge of death invest heavily in

fruit production

http://williamcullina.com/Page58.html

Triploid Bananas and

Parthenocarpy—fruit

production without seeds

Seedless fruits,

sometimes pollination

is necessary; fertilization

is not.

Cacao (Theobroma cacao)

Cauliflory

Avocados (Persea americana)

Protogyny

Group A plants

Group B plants

Sexual Secrets of Figs

• Important wildlife fruit in many tropical forests—‖Keystone Species‖

• Tight relationship with wasp pollinators

• Flowers hidden within flasks ―syconia‖—

Pollination of Figs

Sisson, R.F. 1970. The wasp that plays cupid to a fig.

National Geographic 138:690.

Female wasp travels to fig

Searching for suitable flowers

(i.e., short-styled flowers) for egg laying.

Fig Pollination

Caprifig—female flowers

are parasitized by wasps;

Caprifig is the ―pollenizer‖; male

flower development is timed to

the life cycle of the wasp.

Caprifig is unedible—crunchy,

fibrous, seedy

Short-styled

Female

Flowers

Ostiole

Female Male

Syconium I

Caprifig-unedible

Sexual Secrets of Figs

• Wingless males develop prior to females;

• Males mate with females prior to female emergence;

• Males die in the only home that they have known.

Sisson, R.F. 1970. The wasp that

plays cupid to a fig. National

Geographic 138:690.

Sexual Secrets of Figs

Long-styled

Female

Flowers

Edible Fig—receives pollen as female

wasp travels looking for other fig syconia.

Long-styled flowers in edible fig prohibit

egg laying, but female wasp completes

pollination.

Female with

caprifig pollen

Pollination of Calimyrna Figs

Orchard of

female edible figs.

Bags of pollinator-

Caprifigs are placed

in orchard.

Calimyrna and Black Mission Figs

Ostiole

Black Mission Figs are

PARTHENOCARPIC

and don’t require pollination

for fruit production

Calimyrna figs

require pollination

of long-styled pistillate flowers

in syconia to produce

edible fruits

Papaya Products

• Latex from young fruits

is a source of papain

– Meat tenderizer

– Shrink resistant wool

– Contact lens cleaner

– Dietary supplement

– Spinal disk removal

Sexuality of Papaya

Female plant—pollination is

necessary for fruit production

Male plants produce more

flowers with abundant pollen

Papaya--GMOs

• Selection for cultivars

that produce fruits with

fewer seeds;

• Genetic modification

with genes promoting

parthenocarpy.

• Why have males

around?