Animal Reproductive Strategies: Maximizing Success in Different Environments

1. ANIMAL REPRODUCTIVE STRATEGIES THE ULTIMATE GOAL OF EACH SPECIES Lorraine Kuun, July 2011

2. From CAPS Content Diversity of reproductive strategies • Appropriate examples of different groups in the animal • kingdom to illustrate maximising reproductive success in • different environments: • - external or internal fertilisation • - ovipary, ovovivipary, vivipary • - amniotic egg • - precocial and altricial development • - parental care. Describe the role of the following reproductive strategies in animals in maximizing reproductive success in different environments (using relevant examples): • External fertilisation and internal fertilisation • Ovipary, ovovivipary and vivipary • Amniotic egg • Precocial and altricial development • Parental care Lorraine Kuun, July 2011

3. What is 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. Lorraine Kuun, July 2011

4. REPRODUCTIVE STRATEGIES • External vs Internal fertilisation • Ovipary, ovovivipary and vivipary • Precocial and Altricial development • Amniotic egg • Parental care Lorraine Kuun, July 2011

5. External vs. Internal fertilisation • Disadvantages of external fertilisation (outside the body): • Wasteful; huge loss of energy – many eggs produced, few survive. • Fertilisation not certain. • Environmental conditions important for hatching of eggs Lorraine Kuun, July 2011

6. Lorraine Kuun, July 2011

7. Mating occurs, but no copulation Lorraine Kuun, July 2011

8. Internal fertilisation • 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. • 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). Lorraine Kuun, July 2011

9. Advantages of internal fertilisation Describe advantages here: Lorraine Kuun, July 2011

10. 3.OVIPARY, OVOVIVIPARY, VIVIPARY – terms used to describe what happens when future offspring separates from parent • 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. Lorraine Kuun, July 2011

11. OVIPARY in aquatic conditions • Most fish, amphibians and lower aquatic forms. • Needs large numbers of eggs. Lorraine Kuun, July 2011

12. Shark egg pouch with yolk clearly visible Lorraine Kuun, July 2011

13. OVOVIVIPARY – how is reproduction maximised? • Fewer eggs needed – higher survival rate of offspring. • Developing embryo much less vulnerable to predators. • Developing embryo not subject to environmental changes e.g. temperature. • Young born fully developed, can feed and escape predators more easily. • Occurs in some invertebrates, fish and reptiles. Lorraine Kuun, July 2011

14. Young puff adder being “born alive” after hatching inside mother; note position of cloaca. Lorraine Kuun, July 2011

15. VIVIPARY maximising reproduction • 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 Lorraine Kuun, July 2011

16. Lorraine Kuun, July 2011

17. 4. Precocial vs. Altricialdevelopment eg in Birds PRECOCIAL • Young hatch or born when almost fully developed • Open eyes, hair or down • Active or mobile • Not confined to nests • Energy goes into prenatal development ALTRICIAL • Born or hatched when not well-developed • Often naked, lacking hair or down • Cannot walk or fly • Confined to nest or burrow • Energy goes into parental care after birth Lorraine Kuun, July 2011

18. PRECOCIAL ANIMALS • 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 Lorraine Kuun, July 2011

19. Left: Penguin chick and Above: foal, both mobile soon after birth Lorraine Kuun, July 2011

20. Altricial bird – see mouth-lining that attracts mother Lorraine Kuun, July 2011

21. Altricial: Mice survive in broods, cared for by mother (left); Kittens born weak and totally dependent on mother (below) Human babies Lorraine Kuun, July 2011

22. 5. The Amniotic egg • 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. Lorraine Kuun, July 2011

23. The Amniotic egg • Fertilisation is internal. • Extra-embryonic (not part of embryo) membranes only develop after fertilisation. • Membranes are: • Amnion • Allantois • Yolk sac • Chorion Major evolutionary development; allowed first reptiles to colonise land! Lorraine Kuun, July 2011

24. The Amniotic egg Lorraine Kuun, July 2011

25. How does the amniotic egg maximise reproduction? • 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). Lorraine Kuun, July 2011

26. 6. Parental care • 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: • Prenatal – guarding eggs, building nests, carrying broods, incubating eggs and placental nourishing. • Post-natal – providing food, protecting offspring, teaching offspring. Lorraine Kuun, July 2011

27. Little or no parental care • 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 Lorraine Kuun, July 2011

28. When parental care is given • 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. Lorraine Kuun, July 2011