P1252109112WpFMH

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Sexual reproduction
Thomas Geburek Department of Genetics Federal
Research Centre for Forests, Natural Hazards,
and Landscape (BFW) Austria
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Recall The main source of genetic variation is
recombination!
Sexual reproduction is a very important component
of the genetic system that stores,
transmits, creates, tests
genetic variation.
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Sexual Systems
Dioecious all trees are either male or female
Ginkgo biloba (male)
Ginkgo biloba (female)
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Sexual Systems
Dioecious all trees are either male or
female Hermaphrodite individual tree with both
male and female functioning flowers. It may have
either monoecious flowers (single sex flowers ?
monoecy) or hermaphrodite (bisexual)
flowers. Monoecious hermaphrodite tree in which
male and female gametes are produced in separated
flowers (bisexual) ? sex function
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Sexual Systems
Example Mahagony (Swietenia spec.)
Morphology ? hermaphrodite flowers Functions ?
monoecious flowers, because anthers or
ovaries are vestigial
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red manjack (Cordia collococca)
Flowers are clearly hermaphrodite, but sex
function varies considerably.
Training Workshop on Forest Biodiversity, June
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Monoecious trees are found approx. 75 in
boreal and temperate zones approx. 10 in
tropical zones.
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Sexual Function
Sexual function refers to the frequency of the
effective sexual types. Bisexuality does not
mean that trees function equally as females or
males. In monoecy, the sexual function (S) may
be estimated by the number of effective female
gametes vs. total number of effective gametes. S
varies from zero (exclusively males) to one
(exclusively females)
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Si N ? i /(N ?i N ?i )
Effective number (N) of gametes can only be
roughly estimated. If pollen is in surplus,
census (C) ? can be regarded as effective.
N ? i (C ?i /C ?) C ?
Si C ?i x C ?/ (C ?i x C ? C ?i C ?)
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Malaysian example
Garcinia scortechinii tended towards femalenees
in a censused 25 ha area in the Pasoh Forest
Reserve (West Malaysia). No males recorded,
however 68 of the adult trees fruited (Thomas
1997). Sexual function S 1.0
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Sexual Function and Structure
1.0
Relative Proportion
0.5
Sexual function
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Dioecy excludes self-pollination thus reduces
coancestry among offspring.
In bisexual plants coancestry is reduced by

• incompatibility systems,

• avoidance of self-pollination by spatial
  separation of males and female stroboli.

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Dioecy excludes self-pollination thus reduces
coancestry among offspring.
In bisexual plants coancestry is also reduced by

• incompatibility systems,

• avoidance of self-pollination by spatial
  separation of males and female stroboli,

• temporal separation of the flowers (protogyny or
  protandry)

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Incompatability Systems
homomorphic gametophytic self-incompatibility
Gene product are ribonucleases (S-RNA-ases)
expressed in the pistil constituting a barrier
for certain pollen tubes.
S-RNA-ase encoded by the same S-allele (from the
maternal tree) reacts with the cytoplasm of the
pollen carrying the same S-allele through
enzymatic degradation of the r-RNA of the pollen
tube.
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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(1) Homomorphic gametophytic self-incompatibility
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Consequences Prevents selfing and mating with
closely related trees. Number of incompatability
alleles determines number of possible crosses.
Example Leucaema diversifolia
Training Workshop on Forest Biodiversity, June
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Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Incompatability Systems
homomorphic sporophytic self-incompatibility
Diploid genome of the pollen grain reacts with
the diploid tissue of the receptive plant.
Sharing of only one incompatibility allele
between prospective mates prevents reproduction
success.
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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(1) Homomorphic sporophytic self-incompatibility
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Consequences Prevents selfing and mating with
trees sharing only one incompatability
allele. Number of incompatability alleles
determines number of possible crosses.
Example Ulmus
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Heteromorphic sporophytic self-incompatibility
Heterostyly
ss Ss ss no yes Ss yes no
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Example Cordia alliodora
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Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Papaya (Carica papaya)

• fruit tree
• indigeneous to the American tropics
• dioecious

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Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Female (pistillate) tree functional ovary , no
stamens, pollination from separate trees
genotype mm Male (staminate) tree no ovary,
only stamens genotype M1m Hermaphroditic tree
low temperature gives a shift to femaleness,
high temperature gives a shift to maleness -
genotype M2m
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Possible crosses
mm (pistillate) x M1m (staminate) ? 1 mm 1
M1m M2m (hermaphroditic) x M2m (hermaphroditic)
? 1 M2M2 (lethal) 2 M2m 1 mm (pistillate)
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Incompatability Systems
post-zygotic

• Conifers have no pre-zygotic incompatibility
  system.

• Embryonic abortion due to early acting inbreeding

• lethal recessive mutants

embryonic lethal equivalents or embryonic lethals
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Embryonic lethals

• Different models

• Number can be estimated by

Embryonic lethals
- 4 log e x relative self fertility
relative self fertility
sound seed set after self-pollination
sound seed set after cross -pollination
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2006, Kuala Lumpur, Malaysia
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Embryonic lethals
post-zygotic
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Prediction of empty seeds and proportion of
selfed seeds (example for 10 embryonic lethals)
empty seeds
proportion of selfed seeds
Selfed Pollen
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Pollination and pollen movement

• Wind-pollinated tropical species, e.g. Shorea
  robusta, Artocarpus heterophylla, Atelia
  herbert-smithii.

• Wind-dispersed pollen are produced in surplus and
  distributed undirectionally.

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Pollination and pollen movement
Morphology of ovulate cone maximizes the
probability of species- specific pollen capture
through close-proximity interaction.
Unidirectional wind is deflected into cyclonic
vortices.
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Pollination and pollen movement
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Pollination and pollen movement
Fd F0 e -kd
? 1.205 kg/m3, µ 1.83 x 10 -5 kg/m s
Pollen Frequency
Distance
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Stokes law Estimation of the sedimentation
velocity of spherical bodies
r radius of the pollen grain (m), g gravity
(m/s2), d density of pollen (kg/m3), ?
density of air (kg/m3), µ viscosity (absolute)
of air (kg/m s).
? 1.205 kg/m3, µ 1.83 x 10 -5 kg/m s
European example Larix decidua experimental ?
0,130 m/s predicted ? 0,127 m/s
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Pollination and pollen movement
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Pollination and pollen movement
Effective pollen distribution can be studied by

• pollen trapping of single trees

• pollen trapping of radioactive-labelled sources

• paternity analysis.

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Animal-pollinations enhanced by visual
cues Showy petals or sepals with obvious shape,
size, and color. Butterflies and birds are
attracted to red and yellow colors. Bees have
vision that is shifted toward the blue end of our
visible spectrum. White or very pale color are
importsant for nocturnal vectors. olfactory
cues rewards for the visiting vector (pollen,
nectar)
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Vector related questions Alternate host species
to provide food ? Example Byrsonia
crassifolia Pattern of vector movement e.g.
trap lining day to day repeated vector
movement over a relatively large area (larger
bees, bat, butterfly, hummingbirds), typical for
trees with relatively few flowers over extended
periods ? pronounced long distance gene flow, non
random mating events
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Mass flowering tree species ? Higher selfing
rate, close-distance intertree movement
Example Moca (Andira inermis) 70 bee species,
only 8 were conspecific)
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Mating
Outcrossing rates may vary

• from year to year

• within the crown (in the apex higher rates)

• with stand density.

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Mating
Species Number of Pops Multilocus outcrossing rate (tm) Range of tm References
Acacia auriculiformis 2 .92-.93 Moran et al. (1989)
Acacia crassicarpa 2 .93-.99 Moran et al. (1989)
Berthollethia excelsa 1 .85 OMalley et al. (1988)
Brosimum alicastrum 1 .88 Hamrick Murawski (1990)
Cavanillesia platanifolia 2 .21-.66 Hamrick Murawski (1990)
Carapa procera 2 .63-.85 Doligez Joly (1997)
Cordia alliodora 1 .98 Boshier et al. (1995)
Caryocar brasiliense 4 1.00 Collevatti et al. (2001)
Cecropia obtusifolia 1 .97 Alvarez-Bylia Garay (1994)
Dryobalanops aromatica 3 .67-.92 Lee (2000)
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Species Number of Pops Multilocus outcrossing rate (tm) Range of tm References
Enterolobium cyclocarpum 2 .99-1.00 Rocha Aguilar (2001)
Eucalyptus grandis 21 .84 Eldridge et al. (1993)
Eucalyptus urophylla 2 .90-.91 House Bell (1994)
Pithecellobium pedicilare 1 .95 OMalley Bawa (1987)
Platypodium elegans 1 .92 Hamrick Murawski (1990)
Pterocarpus macrocarpus 11 .72-.96 Liengsiri et al. (1998)
Psychotria faxlucens 2 1.00 Perez-Nasser et al. (1993)
Shorea congestifolia 1 .87 Murawski et al. (1994)
Shorea leprosula 1 .84 Lee et al. (2000)
Shorea trapezifolia 2 .54-.62 Murawski et al. (1994)
Tachigali versicolor 6 1.00 Loveless et al. (1998)
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By now you should know ...........
Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Natural seed dissemination (migration)
Wind-dispersed
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Apomixis (asexual embryogenesis)
Ability to reproduce asxually through seeds

• seeds carry exclusively maternal genes

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Pollination and pollen movement
pollen/cm2
species
Larix Picea Pinus

• Wind-dispersed pollen are produced in surplus.

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Pollination and pollen movement
pollen/cm2
species
Larix 1300 Picea 18 000 Pinus 31 000

• Wind-dispersed pollen are produced in surplus.

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia
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Pollination and pollen movement
Different pollination systems in conifers
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2006, Kuala Lumpur, Malaysia
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Mating
Many tree species have a mixed-mating system.
Outcrossing rates obtained by means of

• chlorophyll defect mutants

• rare marker genes

• gene markers (isozymes, DNA)

Training Workshop on Forest Biodiversity, June
2006, Kuala Lumpur, Malaysia