JR

Notes on Reproductive Strategies and Fertilisation

Reproductive strategies

  • Two main types: r-strategy and K-strategy

    • r-strategy:

    • Turtles expend a lot of energy producing many offspring, but little in parental care.

    • Many offspring will die before adulthood, but enough survive to continue the species.

    • K-strategy:

    • Lions and elephants produce fewer offspring but expend enormous amounts of energy on parental care.

    • Offspring have a better chance of surviving to adulthood.

  • Survivorship curves:

    • Illustrates the number of organisms that survive at different stages of their life span.

    • K-strategy / r-strategy context mention.

  • Reproductive strategies:

    • Animals use various reproductive strategies to increase their reproductive success.

    • These strategies are structural, functional and behavioural adaptations to increase the chances of fertilisation and survival of offspring.

  • Various strategies:

    • Courtship

    • External vs Internal Fertilisation

    • Ovipary, Ovovivipary and Vivipary

    • Amniotic egg

    • Parental care

Courtship

  • Courtship is the behavioural patterns of male and female animals that lead to mating and offspring.

  • Purpose:

    • Ensures both sexes are ready for mating

    • Helps identify mating partners

    • Helps to choose suitable mating partner

  • Courtship takes place in various ways:

    • Visual stimuli

    • Sound stimuli

    • Chemical stimuli

    • Physical movements

External vs Internal Fertilisation

  • Fertilisation is the fusion of the egg and sperm to form a diploid zygote.

  • There are 2 types of fertilisation:

    • External fertilisation

    • Internal fertilisation

  • Key definitions (terminology from slides):

    • Fertilisation: Process during which the sperm fuses with the egg to produce a diploid zygote. Use in sentence: Fertilisation results in the formation of a zygote. 2n (diploid) formation.

    • External fertilisation: Process during which the sperm fuses with the egg outside the female’s body. Use in sentence: During external fertilisation all the sperms may not reach the egg.

    • Internal fertilisation: Process when the sperm fuses with the egg inside the female’s reproductive organs. Use in sentence: Internal fertilisation is a more certain process.

    • Ovipary: A method of reproduction in which eggs are laid and development of these eggs occur outside the mother’s body.

    • Ovovivipary: Eggs develop within the mother’s body and hatch inside the mother’s body before being born. Internal fertilisation has taken place. The young get their nutrition from the yolk, not the mother.

    • Vivipary: The young develops inside the mother’s uterus after internal fertilisation. During development the young receive nutrients from the mother’s blood via the placenta. Parental care takes place.

External Fertilisation

  • Large number of gametes produced to increase chances of fertilisation and number of offspring.

  • No parental care.

  • Examples: frogs and fish.

  • The importance of water during external fertilisation:

    • Keeps the eggs moist, thus preventing them from drying out.

    • Medium in which sperms swim towards the egg.

Internal Fertilisation

  • This is process where the sperm fuses with the egg inside the female body.

  • No water is required for internal fertilisation. This makes it an adaptation for terrestrial life.

  • Fewer gametes are produced as success of fertilisation is much greater.

  • Examples: birds and mammals, including humans.

Ovipary, Ovovivipary and Vivipary

  • Ovipary (egg-bearing):

    • Eggs are laid and development occurs outside the mother’s body.

    • Eggs can be fertilized internally or externally after they have been laid.

    • The egg will hatch into a young animal.

    • Most invertebrates and many vertebrates reproduce this way.

    • Examples: pythons and hens.

  • Ovovivipary:

    • Eggs are produced but develop within the mother’s body and may hatch within the mother’s body.

    • Internal fertilisation has taken place.

    • The young get their nutrition from the yolk, not the mother.

    • Examples: puffadder and reptiles.

  • Vivipary:

    • The young develops inside the mother’s uterus after internal fertilisation.

    • During development the young receive nutrients from the mother via the placenta.

    • Parental care takes place.

    • Examples: hammerhead sharks and humans.

  • Terminology recap:

    • Ovovivipary versus Vivipary versus Ovipary – key definitions above.

Amniotic egg

  • All amniotes form eggs with extra-embryonic membranes after fertilisation.

  • These membranes are filled with fluid.

  • Example – a chicken egg.

  • Importance of the amniotic egg:

    • The shells are important because they reduce dehydration (waterproof).

    • Enables these animals to live in a wide range of terrestrial habitats, when compared to amphibians. No need to be close to water.

    • Shell provides protection for the organism.

    • The egg nourishes the organism (yolk sac).

    • Increased chance of survival.

  • Components of the Amniotic Egg and their functions:

    • Amnion: The innermost membrane that surrounds the embryo, filled with amniotic fluid that protects the embryo against mechanical shock.

    • Chorion: The outermost membrane, responsible for gaseous exchange.

    • Allantois: Stores waste substances produced by the embryo and also assists in gaseous exchange.

    • Yolk sac: Serves as food (nourishment) for the embryo.

    • Egg shell: Reduces dehydration and provides protection for the organism.

Parental care

  • It refers to the ways in which parents increase the chances of survival of their offspring until they reach sexual maturity.

  • Some examples of parental care:

    • Guarding eggs

    • Incubation of eggs

    • Keeping young warm

    • Feeding young

    • Protection from predators

Terminology recap

  • Fertilisation: process during which the sperm fuses with the egg to produce a diploid zygote.

  • External fertilisation: process during which the sperm fuses with the egg outside the female’s body.

  • Internal fertilisation: process during which the sperm fuses with the egg inside the female’s reproductive organs.

  • Ovipary: a method of reproduction in which eggs are laid and development of these eggs occur outside the mother’s body.

  • Ovovivipary: refers to a type of reproduction in which eggs develop within the mother’s body and hatch inside the mothers body before being born.

  • Vivipary: the type of reproduction in which the young develops inside the mother’s uterus after internal fertilisation.

  • Parental care: It refers to the ways in which parents increase the chances of survival of their offspring.

Terminology usage reminders (from slides)

  • External fertilisation: Eggs laid and fertilised outside the female body, typically in water.

  • Internal fertilisation: Sperm deposited inside the female reproductive tract.

  • Amniotic egg: Egg with extra-embryonic membranes and a protective shell in amniotes.

Practice questions (with solutions)

  • Question 1: Method of reproduction in which the foetus is nourished through an umbilical cord is…

    • A: Ovipary

    • B: Vivipary

    • C: Both A and B

    • D: Neither nor B

    • Answer: B

  • Question 2: The method of reproduction in which the young hatch from eggs outside the mother’s body…

    • A. Vivipary

    • B. Ovipary

    • C. Ovovivipary

    • D. None of the above

    • Answer: B

  • Question 3: The liquid that protects embryo against mechanical shock…

    • A. Chorion

    • B. Allantois

    • C. Amnion

    • D. Yolk sac

    • Answer: C

  • Question 4: Allows for gaseous exchange only…

    • A. Chorion

    • B. Allantois

    • C. Amnion

    • D. Yolk sac

    • Answer: A

  • Question 5: Stores waste substances produced by the embryo…

    • A. Chorion

    • B. Allantois

    • C. Amnion

    • D. Yolk sac

    • Answer: B

  • Question 6: Serves as food for the embryo …

    • A. Chorion

    • B. Allantois

    • C. Amnion

    • D. Yolk sac

    • Answer: D

  • Question 7: Reduces dehydration…

    • A. Chorion

    • B. Allantois

    • C. Egg shell

    • D. Yolk sac

    • Answer: C

  • Question 8: Fertilisation that occurs within the female body…

    • A. Internal fertilisation

    • B. External fertilisation

    • C. Both A and B

    • D. None of the above

    • Answer: A

  • Question 9: Fertilisation that occurs outside the female body…

    • A. Internal fertilisation

    • B. External fertilisation

    • C. Both A and B

    • D. None of the above

    • Answer: B

  • Question 10: Method of reproduction in which the young develop from eggs that are internally fertilized and retained within the mother’s body and hatch after development…

    • A. Ovovivipary

    • B. Vivipary

    • C. Ovipary

    • D. None of the above

    • Answer: A

  • Answer key sequence (as given in slide): B, B, C, A, B, D, C, A, B, A