Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox,...

Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 18-1

Part 4: Animal form and function

Chapter 18: Animal reproduction


Reproduction

• Asexual reproduction– one parent– new individuals genetically identical to parent and to each

other

• Sexual reproduction– two parents– new individuals genetically unique (novel combination of

genes from both parents)


Asexual reproduction

• New individuals produced through mitotic cell division

• Limited genetic diversity• Occurs by:

– regeneration– budding– parthenogenesis


Regeneration

• Production of new individuals– cellular replication by mitosis– differentiation of tissues

• Reproduction by fragmentation– example: aquatic annelids

• Regeneration of individuals from body parts– example: starfish


Budding

• Production of new individuals– outgrowth of body wall of parent

• Break off to form individual– example: Hydra

• Remain attached to form part of colony– example: corals


Parthenogenesis

• Production of new individuals– egg cells develop into embryos without fertilisation– offspring usually female

• Obligate parthenogenesis– example: Heteronotia binoei (Binoe’s gecko)

• Cyclical parthenogenesis– example: some species of aphids

(cont.)


Parthenogenesis (cont.)

• Ants, bees and wasps (Hymenoptera)– females produced by sexual reproduction– males produced by asexual reproduction

(parthenogenesis)

• Unfertilised eggs (n)– undergo mitosis– but do not divide into two cells– nuclei fuse to produce a diploid cell (2n)– cell develops as if fertilised


Sexual reproduction

• New individuals produced through fusion of haploid cells (gametes) from parents

– egg (ovum)– sperm (spermatozoon)

• Increases genetic diversity


Gametes

• Two types of gametes• Similar structure

– isogamy

• Different structure– anisogamy– smaller of gamete pair = male


Male and female

• Different mating types = sex– male, female

• Males– produce sperm only

• Females– produce eggs only


Mating systems

• Organisms with separate sexes– dioecious

• Organisms with both sexes in one individual– monoecious or hermaphroditic


Hermaphroditism

• Hermaphrodites produce male and female gametes

• Problems of self-fertilisation limited by separation of male and female gametes

– anatomy male and female reproductive tracts separate

– behaviour complex courtship and mating

– time eggs become fertile after sperm are no longer functional sex change


Changing sex

• Some species avoid self-fertilisation by sex changes

– alternate between male and female at different stages of life cycle

• Male female– protandry

• Female male– protogyny


Reproductive strategies

• Developmental strategies vary• Indirect development

– offspring pass through one or more larval stages before they attain adult form

• Direct development– offspring hatch or are born resembling miniature adults


Indirect development

• Many eggs produced– small amount of yolk in each egg– limits time for embryonic development

• Free-living larval forms• Metamorphosis (change in form from larva to

adult)– example: butterflies, flies, beetles– example: frogs


Fig. 18.8: Indirect development

(a)

(b)

Copyright © 18.8a D Parer & E Parer-Cook/AUSCAPE Copyright © 18.8b Kathie Atkinson


Direct development

• Few eggs produced– large amount of yolk in each egg– embryo nourished by yolk

• Embryo develops in egg• Hatches/born with adult form

– example: land snails, reptiles, birds– example: mammals


Fig. 18.9: Direct development

Copyright © 18.9 Jan Aldenhoven/AUSCAPE


Development in mammals

• Direct development– but eggs have small amount of yolk

• Young develop in uterus• Nutrients provided to developing young

– before birth uterine secretions placenta

– after birth milk

(cont.)


Development in mammals (cont.)

• Variation in patterns of reproduction– young born at different stages of development

• Monotremes– lay eggs (oviparous)

• Marsupials and eutherians– live young (viviparous)


Costs of sexual reproduction• Parental investment in reproduction

– varies depending on reproductive strategy

• Includes– production of gametes– increased risk of predation– competition for mates– parental care

• Cost must not outweigh benefit• Caring for young

– increases chances of offspring surviving to maturity– reduces ability of one (or both) parents to find food and

avoid predators


Gametogenesis

• Primary sex organs = gonads• Male gonad = testis

– produces sperm (spermatozoa)

• Female gonad = ovary– produces eggs (ova)

• Process of gamete production = gametogenesis– spermatogenesis– oogenesis


Mitotic divisions

• Primordial germ cells undergo a series of mitotic divisions

• Give rise to multiple diploid (2n) oogonia/ spermatogonia

• After the final mitotic division, these cells are termed oocytes/spermatocytes


Meiotic divisions• Primary oocyte (product of mitotic divisions)• First meiotic division

– primary oocyte gives rise to secondary oocyte first polar body

• Second meiotic division– secondary oocyte

ovum (egg) second polar body

– first polar body polar bodies

(cont.)


Meiotic divisions (cont.)

• Primary spermatocyte (product of mitotic divisions)• First meiotic division

– primary spermatocyte gives rise to secondary spermatocytes

• Second meiotic division– secondary spermatocytes

spermatids


Fig. 18.19a: Oogenesis


Fig. 18.19b: Spermatogenesis


Maturation of gametes

• Spermatocyte– loss of most of cytoplasm– development of long flagellum (tail)– formation of secretory acrosome at anterior of head

section

• Oocyte– increase in organelles– increase in nutritive materials– development of protective extracellular membranes e.g.

vitelline membrane


Fertilisation

• Fusion of egg and sperm• Egg activation

– inactive egg is activated by fusion of plasma membranes of egg and sperm

– resumes synthetic activity

• Nuclear fusion– pronuclei of egg and sperm fuse– creates diploid zygote


Methods of fertilisation

• Methods of bringing egg and sperm together• External fertilisation

– takes place outside body– examples: corals, frogs

• Internal fertilisation– takes place inside body– examples: land snails, mammals


Internal fertilisation

• Sperm must be transferred to female reproductive tract

• Intromittent organ– penis, claspers

• Spermatophore– packet of sperm

• Injected through body wall– example: leeches

Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox,...

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