Sexual reproduction
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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. Recall: The main source of genetic variation is recombination!.

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Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

Sexual Systems

Example: Mahagony (Swietenia spec.)

Morphology  hermaphrodite flowers

Functions  monoecious flowers, because anthers or ovaries are vestigial

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


Sexual reproduction

red manjack

(Cordia collococca)

Flowers are clearly hermaphrodite, but sex function varies considerably.

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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 ♀iC ♀)

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


Sexual reproduction

Malaysian example

Garciniascortechinii 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


Sexual reproduction

0

1.0

0.5

Sexual Function and Structure

1.0

Relative Proportion

0.5

Sexual function

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

(1) Homomorphic gametophytic self-incompatibility

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


Sexual reproduction

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 2006, Kuala Lumpur, Malaysia


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

(1) Homomorphic sporophytic self-incompatibility

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


Sexual reproduction

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


Sexual reproduction

Heteromorphic sporophytic self-incompatibility

Heterostyly

ssSs

ssnoyes

Ssyesno

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


Sexual reproduction

Example: Cordia alliodora

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


Sexual reproduction

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


Sexual reproduction

Papaya (Carica papaya)

  • fruit tree

  • indigeneous to the American tropics

  • dioecious

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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

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


Sexual reproduction

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

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


Sexual reproduction

Embryonic lethals

post-zygotic

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


Sexual reproduction

Prediction of empty seeds and proportion of selfed seeds (example for 10 embryonic lethals)

empty seeds

proportion of

selfed seeds

Selfed Pollen

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

Pollination and pollen movement

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


Sexual reproduction

Pollination and pollen movement

Fd = F0e-kd

ρ = 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


Sexual reproduction

Stoke‘s law – Estimation of the sedimentation velocity of spherical bodies

r = radius of the pollen grain (m),

g = gravity (m/s2),

δ = density of pollen (kg/m3),

ρ = density of air (kg/m3),

μ = viscosity (absolute) of air (kg/m s).

ρ = 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


Sexual reproduction

Pollination and pollen movement

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

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


Sexual reproduction

Mating


Sexual reproduction

By now you should know

...........

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


Sexual reproduction

Natural seed dissemination (migration)

Wind-dispersed


Sexual reproduction

Apomixis (=asexual embryogenesis)

Ability to reproduce asxually through seeds

  • seeds carry exclusively maternal genes

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


Sexual reproduction

Pollination and pollen movement

species

pollen/cm2

Larix

Picea

Pinus

  • Wind-dispersed pollen are produced in surplus.

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


Sexual reproduction

Pollination and pollen movement

species

pollen/cm2

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


Sexual reproduction

Pollination and pollen movement

Different pollination systems in conifers

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


Sexual reproduction

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


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