Evolution of Australian Biota and Asexual Reproduction

Evolution of Australian Biota
Topic 10: Reproductive Adaptations in Plants: Seed Dispersal
and Asexual Reproduction
Part of the Evolution of Australian Biota Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
Seed Dispersal
After successful pollination and fertilisation of the flower, the
seed develops. It is an advantage for a plant to spread or
disperse its seeds over a wide distance. This prevents
overcrowding and increases the chances of survival in
situations of environmental change such as fire or disease.
openwalls.com
Seed Dispersal
Seeds are dispersed by
wind or animals such as
insects, birds and mammals
are designed to disperse in
many ways. Australian
native plants have evolved a
variety of adaptations to
aid in the effect and
successful dispersal of their
seeds.
en.wikipedia.org
Wind
Some seeds are
aerodynamically
designed to be blown
long distances by the
wind. For example,
Flindersia,
leptospermums,
melaleucas, native daises
and casuarinas.
tame.ifas.ufl.edu
Animal
Other seeds have structures, such as hooks or barbs, which
cling or stick to the fur or feathers of animals. This is so they
can be carried long distances before they fall to the ground.
Examples include: Pisonia (birdlime tree) and Pittosporum
superstock.com
davesgarden.com
Animal
Other seeds are enclosed in
bright coloured fleshy fruits. Red
is a very conspicuous colour to
birds, so any fruit or berries
containing seeds are highly likely
to be dispersed by birds
(lilypillys). Smaller birds are also
interested in purple berries such
as tree violet (Hymenanthera
dentate)
southgippsland.wordpress.com
Animal
Seeds can pass through the
digestive system of
mammals or birds which
unknowingly transport the
seeds to new locations so
that they germinate on the
spot upon which they were
defecated.
burrard-lucas.com
Animal
Some seeds must pass through the gut of an animal to be able
to germinate. For example the nitre bush (Nitraria billardieri)
depends on emus to eat and spread their seeds. Another
example is the mistletoe, it has sticky seeds which are
deposited on trees by mistletoe birds.
birdway.com.au
Animal
To bribe ants, wattle (Acacia) seeds have some lipids attached
to their outside. The seeds (like Lomandra and Grevillae) are
carried by the ants to their nests where they consume the
lipids but leave the hard seeds underground, safe from fire.
Wattles can then flourish and grow after the hottest of
bushfires.
myrmecos.net
Fire
Eucalypts, banksia and
many other Australian
plants store they seeds
until fire destroys the
branch or the entire plant.
This allows the capsules to
open, releasing the seeds
for dispersal, usually by the
wind.
wombatwal.redbubble.com
Fire
This provides a significant advantage to the seeds as the fire
clears land areas and invites re-colonisation by new plants.
The fastest dispersing and germinating plants can colonise
more area of land.
karencheng.com.au
Fire
Not all banksias and eucalypts
store their seeds waiting for fire.
Banksia integrifolia and Eucalyptus
melanoxylon release their seeds
once it is ripe. This is seen as a
primitive feature compared with
other species that are actually
more suited to their environment
and have more effective colonising
mechanisms.
northsydney.nsw.gov.au
Water
Some seeds rely on water dispersal, such as the water gum
(Syzygium francisii) and the mangrove (Avicennia marina). Seeds
may float small or large distances from the parent plant along
rivers and estuaries or across seas.
ecology.hku.hk
Explosion
Finally, some seeds are violently
propelled from the base of fruit
in an explosive discharge. Seeds
are ejected from the pod at high
speeds caused by the drying and
contraction of the pod. Some
seeds such as the Acacia
cultriformis can be thrown up to 2
metres by this method.
Hand out copy of Table 3.8 (Prelim
Bio in Focus Text)
dmt-nexus.me
Asexual Reproduction
Asexual reproduction is the
making of a new individual
without the use of sex cells
or gametes. Only one
parent is required for the
mitotic cell divisions to
occur.
sbi3uplantsjan2012.wikispaces.com
Asexual Reproduction
Some types of asexual reproduction are:
 Binary fusion
 Budding (Hydra and coral)
 Spore formation (moss, fungi and ferns)
 Vegetation propagation (plant cuttings like roses)
 Regeneration (starfish and earthworms)
 Parthenogensis (Binoe’s gecko)
treatyrepublic.net
Asexual Reproduction
Plants that reproduce asexually
clone new individuals from
portions of the root, stem,
leaves or ovules of adult
individuals. The asexually
produced individuals are
genetically identical to the
parent.
elateafrica.org
Vegetation Reproduction
New plant individuals are simply closed from parts of adults,
such as runners, rhizomes and suckers. Runners are long, thin
stems that grow along the surface of the soil.
treatyrepublic.net
Vegetation Reproduction
In the cultivated strawberry, for example, leaves, flowers and
roots are produced at every other node on the runner. Just
beyond each second node, the tip of the node turns up and
thickens, producing new roots and a new shoot that continues
the runner.
gardenpool.org
Vegetation Reproduction
Another example is
spinifex grass which has
long stems that grow
horizontally along the
surface of the soil. At
each node, leaves and
roots are produced that
can be subdivided into
new plants.
treatyrepublic.net
Vegetation Reproduction
Rhizomes are underground horizontal stems that invade areas
near the parent plant with each node being able to give rise to
a new flowering shoot. Corms, bulbs and root tubers are
stems specialised for storage and reproduction. The eyes or
‘seed pieces’ of the potato give rise to the new plant.
Rhizomes are characteristic of ginger, ferns such as bracken
fern and many grasses.
history-punk.com
Vegetation Reproduction
The roots of some plants
produce ‘suckers’ or sprouts,
which give rise to new
plants. Trees and shrubs that
sucker, such as reeds, wattles
and blackberries can spread
quickly into a vacant patch of
habitat after disturbance.
flickr.com
Budding
Budding is one of the more
unusual forms of asexual
reproduction seen in plants.
Budding involves the
development of a new
individual as an outgrowth
of the parent plant. For
example, Kalanchoe
produces buds along leaf
margins, which can break
off and form new plants.
treatyrepublic.net
Apomixis
In certain plants, such as
kangaroo grass, lemon and
orange trees and
dandelions, the embryos in
the seeds may be produced
asexually from the parent
plant. The seeds produced
in this way give rise to
individuals that are
genetically identical to their
parents.
anbg.gov.au
Apomixis
By reproducing asexually this
way these plants also gain the
advantage of seed dispersal, an
adaptation usually associated
only with sexual reproduction,
as well as the rapid
multiplication of plants.
tki-health-om.blogspot.com
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