2.1 Evolutionary Advantages of Sexual and Asexual Reproduction

Evolution of Australian Biota
Topic 11: Evolutionary Advantages of Sexual and Asexual
Part of the Evolution of Australian Biota Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
DOT Point
 Explain how the evolution of these reproductive adaptations has
increased the chances of continuity of the species in the Australian
As organisms have evolved from aquatic environments moving
onto the land, the evolution of reproductive adaptations has
ensured the survival of species.
Over time, organisms have continued to develop and become
more specialised in their reproductive adaptations surviving in
harsh arid Australian conditions with extremes of drought and
Reproduction is not necessary for individual success, but for
the continuation of the species. There are a number of
strategies of reproduction depending on the environment of
the organism.
Asexual Reproduction
Organisms that reproduce
asexually do not have to rely
on another individual
organism to provide gametes
and are at an advantage when
sudden or unexpectedly
favourable conditions arise
because they can quickly
reproduce themselves.
Asexual Reproduction
This can become a competitive edge if the organism lives in an
environment that is often disturbed, and they are particularly
well suited to a certain environment or habitat. Asexual
reproduction in plants is far more common in harsh
environments where there is little margin for variation.
Asexual Reproduction
Only one parent is required so energy is not wasted on
producing large numbers of gametes or on finding a mate.
This is advantageous in arid conditions. For example, spinifex
grass survives and reproduces successfully by sending out
runners in harsh sand dune conditions.
Asexual Reproduction
Asexual reproduction is a relatively
quick process and large numbers of
offspring can be produced rapidly.
This is an advantage when rapid
recovery is needed after a decline in
numbers (bushfire/drought). The
colony wattle can send up shoots
from the outer roots which grow into
separate plants if the parent shrub
Asexual Reproduction
If there is no variation in the environment then the identical
offspring will always be adapted to their surroundings and
survive to reproduce successfully. Corals, such as the groove
brain coral, reproduce by budding when conditions are
favourable. What might happen to this species if the
environment changes?
Asexual Reproduction
Asexual reproduction allows rapid colonisation after harsh
conditions such as fire or drought. Many Australian plants
have adaptations for survival in this situation where
reproduction is stimulated.
Asexual Reproduction
The main disadvantage to asexual reproduction is if
extremely harsh conditions arise, the whole group of species is
particularly vulnerable to these conditions, or to disease,
parasitism and predation.
Sexual Reproduction
Sexual reproduction produces offspring that are genetically
different and possibly better adapted to new and changing
environmental conditions than their parents. This gives the
species a better chance at surviving in ever-changing
Sexual Reproduction
However, sexual reproduction is often a more energetically
expensive process, compared to asexual reproduction, and
may be the first thing an organism abandons in times of
External Fertilisation
The chances of successful
external fertilisation are
increased by the synchronisation
of the release of gametes,
reproductive cycles and the
mating behaviours of each
species. External fertilisation
and development means parents
spend less time looking after the
young, but more gametes have
to be produced to ensure some
eggs get fertilised.
External Fertilisation
The advantage of this method is
the high dispersal of young. The
gametes are thrown into the sea
and fertilised eggs are carried
away to settle in an area
different to the parents. This
reduces competition for food
and living space and allows
quick recovery of populations
away from damaged areas.
Internal Fertilisation
Organisms that use internal fertilisation tend to be more
adapted to terrestrial environments and reproducing
successfully on land. Fewer gametes are produced because
there is a much higher rate of fertilisation and survival.
Internal Fertilisation
The move to internal
fertilisation and development
has demonstrated new
adaptations for reproduction on
land, which may have started
with the ovules of flowers
becoming enclosed in the ovary
to provide adequate protection
from desiccation.
Parental Care
Parental care varies between aquatic and terrestrial organisms.
Many aquatic species simply abandon the fertilised eggs and
leave them to risk development in the open sea. This means
that less energy is put into caring for the young is much lower;
therefore, more eggs have to be produced to compensate.
Parental Care
Mammals are genetically viviparous (give birth to live young).
Fish, birds and some reptiles and many invertebrates are
oviparous (egg-laying). Oviparous animals will devote varying
amounts of energy to caring for their eggs.
In plants, self-pollination expends less energy in the
production of pollinator attractants and can grow in areas
where the kinds of insects or other animals that might visit
them are absent or very few. These plant species contain high
proportions of individuals well-adapted to their particular
In cross-pollinators, animals
agents such as insects, birds
and mammals have become a
more effective way of
transferring pollen to the
stigma. As flowers become
increasingly specialised, so
do their relationships with
particular groups of insects
and other animals.
Many features of flowering
plants seem to correlate with
successful growth under arid and
semi-arid conditions. The
transfer of pollen between
flowers of separate plants,
sometimes over long distances,
ensures cross-pollination and
may have been important in the
early success of angiosperms.
Reproduction-Australian Species
Individual Australian species have variations in their
reproductive structures and mechanisms. If the environment
changes, the individual species most suited to the changes will
survive, passing on their characteristics to their offspring.
Reproduction-Australian Species
As the Australian environment becomes more arid, organisms
possessing reproductive adaptations that enable their young to
survive should be able to increase in numbers.
Reproduction-Australian Species
Australia has many areas of harsh arid conditions, making it
difficult for effective fertilisation and development.
Reproducing offspring in times favourable to the organism
greatly increases the chance of continuity of the species.
Reproduction-Australian Species
Possessing adaptations for survival and the ability to flourish
after extreme harsh conditions pass also increase chances of
continuity of the species. Many Australian plants possess
adaptations to harsh conditions like fire.
Reproduction-Australian Species
Hakeas have woody seed pods able to survive the high
temperatures of fire. The pods do not usually open unless
stimulated by the heat of fire, landing on soil enriched by ash
from the fire. Seeds are not released until environmental
conditions are favourable.
-Students to complete Revision Questions pg 309

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