1. SEXUAL AND ASEXUAL 2. LIFE CYCLES OF PLANTS AND INSECTS 3. FLOWERS AS REPRODUCTIVE STRUCTURES 4....

1. SEXUAL AND ASEXUAL2. LIFE CYCLES OF PLANTS AND INSECTS3. FLOWERS AS REPRODUCTIVE STRUCTURES4. REPRODUCTIVE STRATEGIES IN ANIMALS

Definition of asexual reproduction:

• No fertilisation• Only one parent• No genetic variation

as opposed to ...Lorraine Kuun, July 2011

Fertilization Two parents Genetic variation

Gametes fuse to form zygote, containing genes from both parents.

Further variation brought about by:1.Crossing over during meiosis, prophase I2.Random assortment and segregation of

chromosomes3.Random fertilisation4.Mutations

Lorraine Kuun, July 2011

1.Binary fission – “splitting in two” – mitosis, e.g. bacterium: Escherichia coli

2. Budding – new individual develops as outgrowth on parent organisms e.g. Yeast cells.

3. Spore production – spores produced during favourable conditions e.g. Fungi

4.Vegetative reproduction – vegetative part of plant, i.e. root, stem of leaf develops into new plant; can be natural or artificial.

Buds on leaf margins e.g. Kalanchoe

Tubers

DISADVANTAGES OF ASEXUAL REPRODUCTION

1.No genetic variation – adaptation may be difficult

2.All share same “weak characteristics” – may die out when environmental conditions change/become unfavourable

3.Mass reproduction can threaten environment – carrying capacity

ADVANTAGES OF SEXUAL REPRODUCTION

1.Genetic variation2.Possible better

adaptations to changing environment

3.Role in natural selection

4.Better chances of survival

DISADVANTAGES OF SEXUAL REPRODUCTION

1.High energy cost – gametes to be produced, gestation, parental care etc.

2.Needs two parents3.Slower, longer process4.Young can be vulnerable to

predators5.Extended periods of parental

care6.Plants may need pollinatorsLorraine Kuun, July 2011

1. Gametophyte: generation producing gametes in gametangium/ gametangia sexual stage.

2. Sporophyte: generation producing spores in sporangium/ sporangia – asexual stage.

NB: In higher plants the generations alternate in the life cycle of a plant; in lower plants reproduction is either through gametes (sexual) or spores etc. (asexual).

1. A haploid gametophyte generation that produces gametes (n) by mitosis ...

the gametes (n) fuse toform zygote (2n), the start of ...

2. A diploid sporophyte generation that

produces spores (n) by meiosis.

Leaf-like structures of moss gametophyte

Sporangium of moss sporophyte

INSECT METAMORPHOSIS

Physical changes from one stage in life cycle to another.

TWO TYPES OF METAMORPHOSIS:

1. Complete metamorphosis

2. Incomplete metamorphosis

88 % of all insects 12 % of insects

COMPLETE Four stages: 1. egg 2. larva 3. pupa 4. adult

E.g. Butterflies, bees, housefly

INCOMPLETE Three stages: 1. egg 2. nymph 3. adult

E.g. Locust, cricket, cockroach

Advantages:1.Vulnerable pupa

stage avoided.2.Less energy is

needed – no drastic changes from pupa to adult.

3.All stages can eat same food.

Disadvantages:1.Nymph and adult often

compete for same food.2.Insect vulnerable to

dehydration and predators when moulting.

3.Entire insect population could be threatened by environmental changes.

1. Male (no pistil) or female (no anthers) flowers on different plants – dioecious.

2. Protandry – pollen ripe before stigma is receptive.

3. Protogyny – stigma receptive, but pollen not ripe yet.

i.e. self-pollination is prevented.

Most pollinators are insects e.g. Bees, moths, butterflies, beetles.

Some vertebrates also pollinate flowers e.g. Bats, mice, birds (mainly).

Many flowers are pollinated by wind.

Bright colours (bees cannot see red), white for night pollinators e.g. moths

Often sweet scent (attracts moths and butterflies)

Reward of nectar and pollen Contrasting markings on petals to locate

centre of flower (usually not visible to human eye – ultraviolet)

Pollen cling to hair on insect bodies

High yield of dilute nectar Bigger than most insect-pollinated flowers Open in daytime, often red Sturdy against rough feeding of birds Little or no scent – birds have poor sense of

smell Protect ovary against beaks by being

inferior or by partition Pollen sticks together in clumps Often erect or with landing platform for

birds that do not hover

Flowers do not have scent, nectar or brightly coloured petals – no need to attract pollinators.

Flowers high on plant to be exposed to wind. Flowers usually small and reduced, lacking

calyx or corolla (sepals and petals). Anthers large and well-exposed. Masses of light, non-sticky pollen produced. Stigmas long and feathery with large area

for trapping pollen.

The fruit develops from the following layers:

• Fruit wall from ovary wall.

• Seed from ovule.

A seed consists of a

1. Seed coat – outer layer of ovule (pericarp).

2. Embryo – from fertilisized egg cell (zygote undergoes mitosis).

Endosperm – result of double fertilization. Endosperm is food for embryo – also why we eat seeds for food.

Resistant to unfavourable conditions as they have seed coat.

Can be dispersed effectively (see later). Can remain viable in dormant state for long

periods. Seeds have stored food reserve in

endosperm or cotyledons; includes starch, oils and or protein.

Important to man as they are cheap form of plant propagation, way to store plants and are a store of food.

Dormancy is a state of rest. Embryo inactive, seed will not germinate.

Some plants have obligatory period of dormancy – seed will not germinate even if conditions are favourable.

Dormancy prevents seeds from hatching in wrong season when seedlings would be exposed to unfavourable conditions. Allows seeds to survive unfavourable conditions.

Allows for seed dispersal agents to act.

Wind – seeds are light with plumes or wings.

Animals – hooks and thorns – cling to wool, stick in paws.

Humans – edible fruit – seeds egested in different position.

Water – seeds contain oil or air bubbles – float away.

Self-dispersed – fruit dry, dehiscent.

COCO DE MER drifts along ocean currents

Most important plant source of food for humans.

Practical form of food – easy to transport and store for long periods of time.

Grains – wheat, maize (mealies), sorghum, rice, oats; mainly starch

Pulses (legumes) – beans, peas, soy beans, peanuts, lentils, plant proteins

Nuts – oily seeds in hard shells e.g. walnuts, cashews, pecans etc.

Many plant species under threat. Seed bank stores seeds of wild plants and crops. UK – conserves seeds of about 10% of wild plant

species at Kew – Millennium Seed Bank Project. Swedish International Seed Vault – reinforced

concrete tunnel – 4,5 million seed samples – will remain viable for 1000’s of years.

MSBP working with SA National Biodiversity Institute – contributing 2500 indigenous species – endangered, endemic, over-exploited

Can be used to 1. re-establish damaged, lost habitats and

ecosystems2. re-introduce extinct, endangered or

threatened species3. provide research material

THANK YOU

THE ULTIMATE GOAL OF EACH SPECIES

To produce the maximum number of surviving offspring ...

while using the least amount of energy.

This is called the reproductive effort.

1. Courtship2. External vs Internal fertilisation3. Ovipary, ovovivipary and

vivipary4. Precocial and Altricial

development5. Amniotic egg6. Parental care

Simple strategies include pheromones (chemical), brightly coloured body parts (visual) and mating calls (auditory) stimuli.

Complex strategies, unique to species, include courtship displays, annual rut (period of sexual excitement), lek breeding system, courtship-feeding.

Courtship display strategies unique to each species; can include movement, calls, seasonal colour patterns etc.

Bluecrane male trying to attract female’s attention by an elaborate dance

1. Females will be in peak condition to nurture developing baby.

2. Young are born when enough food is available to enable them to reach reproductive age.

Above: male springbok displayLeft: male cichlids make bowersfor females to lay eggs

Male hoopoe feeds female; if she accepts, they will mate

Males and females find suitable mates e.g. male with best genetic potential.

Sexual behaviour in courtship is timed so that male and female both ready for mating at same time.

Energy expenditure by male; female conserves energy for breeding.

Disadvantages of external fertilisation (outside the body):

1.Wasteful; huge loss of energy – many eggs produced, few survive.

2.Fertilisation not certain.3.Environmental conditions important for hatching of eggs

1. Huge numbers of eggs increases probability of fertilisation.

2. Courtship rituals ensure that males and females are closer to each other.

3. Eggs of marine species release species-specific chemotactic factor to attract sperm.

4. Spawning is timed to occur when ocean currents can disperse eggs e.g. sessile species.

5. Young easily dispersed by sea currents; reduce competition.

6. No complicated physical mating, using energy.7. Larval form gets food directly from

environment; no energy input from parent.Lorraine Kuun, July 2011

Mating occurs, but no copulation

Occurs in insects and terrestrial vertebrates i.e. birds, reptiles and mammals.

Marine mammals and some fish e.g. sharks and rays also have internal fertilisation.

Mating and copulation occurs. Most animals have cloaca – common opening

for reproduction and egestion – during fertilisation cloacas are lined up.

Male insects and mammals have a penis – organ to transfer sperm to body of female.

Fluid inside female provide medium for sperm to swim towards egg cell(s).

1. Fertilisation is more certain – gametes placed closer together. Fewer gametes needed.

2. Energy saved in producing fewer gametes can be used for other purposes.

1. Yolk to feed young.2. Shells that enclose eggs (oviparity); better

protection increases survival rate.3. Some fertilised eggs very well-protected

e.g. Sharks (ovoviviparity) and mammals (placenta).

4. Less wastage of gametes – in humans one egg per month produced.

There is a disadvantage: a cooperative partner is needed!

OVIPARY – eggs are released and develop outside body of female, fertilisation internal or external, egg yolk only nutrition.

OVOVIVIPARY – Internal fertilisation, egg shell soft, eggs hatch inside body, appears to be born alive, egg yolk nutrition, mother for protection.

VIVIPARY – fertilisation internal, no egg shell, nutrition via placenta.

Most fish, amphibians and lower aquatic forms.

Needs large numbers of eggs.Larval stage self-sufficient; don’t compete with parents – use different food sources.

Eggs and larvae easily dispersed.

Invertebrates produce large numbers of eggs to ensure survival (no or little parental care).

Protective shell prevents embryo from drying out.

Fewer eggs in e.g. birds and reptiles – energy can be used for more food in egg (yolk and albumin), hatching and protection, parental care.

Development of amnion important factor in success.

Hard shell good protection for developing embryo; prevents embryo from drying out.

Shark egg pouch with yolk clearly visible

1. Fewer eggs needed – higher survival rate of offspring.

2. Developing embryo much less vulnerable to predators.

3. Developing embryo not subject to environmental changes e.g. temperature.

4. Young born fully developed, can feed and escape predators more easily.

5. Occurs in some invertebrates, fish and reptiles.

Young puff adder being “born alive” after hatching inside mother; note position of cloaca.

Occurs in placental mammals, some sharks and scorpions

Fertilisation internal, no shell Placenta responsible for nutrition – young

born alive

1. fewer eggs necessary 2. energy available for nourishment and

protection of embryo, as well as parental care

Ground-nesting birds e.g. Penguins, domestic poultry, ostriches

Large mammals e.g. Elephants, species of antelope, horses etc

Allows young to fend for itself, feed and stay warm

Stay with herd for protection against predators

Learn from older individuals in herds OFFSPRING HAS GOOD CHANCE OF SURVIVAL

Left: Penguin chick andAbove: foal, both mobile soon after birth

Small animals that produce big litters e.g. mice, rats, cats, dogs

Tree-nesting birds that have nests away from predation

Humans (see human reproduction) Altricial species need parental care for a

long time – usually female that does the caring, male sometimes involved.

Birds usually have mouth-lining or gape-edge

Mammals small and immature brains

Altricial bird – see mouth-lining that attracts mother

Mice survive in broods, cared for by mother (left);Kittens born weak and totally dependent on mother (below)

Adaptation of later vertebrates; can lay eggs in terrestrial environment.

Amniotic egg has fluid-filled, extra-embryonic membranes that prevents embryo from drying out.

Earlier vertebrates lay eggs in water; need to return to water/live in water to reproduce.

Amniotic egg lessens dependence on water for reproduction.

Fertilisation is internal. Extra-embryonic (not part of embryo)

membranes only develop after fertilisation. Membranes are:1. Amnion2. Allantois3. Yolk sac4. Chorion

Major evolutionary development; allowed first reptiles to colonise land!

The fluid-filled amnion surrounds and protects the embryo, especially against dehydration and shock.

Allantois acts as reservoir for nitrogenous waste in birds and reptiles.

Yolk sac holds nutritious food for development of embryo.

Chorion surrounds all other membranes: in birds it allows for gaseous exchange; in mammals it forms the placenta (taking over functions of allantois and yolk sac, amongst others (see human reproduction).

Any pattern of behaviour in which parent spends time or energy to improve the 1survival, 2condition and 3future reproductive success of offspring.

Care can be given at any stage:1.Prenatal – guarding eggs, building nests,

carrying broods, incubating eggs and placental nourishing.

2.Post-natal – providing food, protecting offspring, teaching offspring.

Little or no parental care means a low reproductive effort.

Reproductive energy put into producing masses of eggs.

High mortality rate amongst eggs as well as young.

Few individuals survive to reproductive age. E.g. Most fish, amphibians, insects, most

reptiles

Few eggs or young produced. Low mortality rate amongst eggs or young. High reproductive effort. Reproductive energy goes into parental

care after birth (post-natal). Most offspring survive to reproductive age. E.g. Mammals, birds, some reptiles,

exceptions amongst fish and Arthropods.

Left: Midwife toad

Right: chicken laying egg, mother feeding young

Ovovivipary type of parental care

Left: Male seahorse with young emerging from breeding pouch

1. SEXUAL AND ASEXUAL 2. LIFE CYCLES OF PLANTS AND INSECTS 3. FLOWERS AS REPRODUCTIVE STRUCTURES 4....

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