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ANIMAL REPRODUCTIVE STRATEGIES

ANIMAL REPRODUCTIVE STRATEGIES. THE ULTIMATE GOAL OF EACH SPECIES. 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 .

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ANIMAL REPRODUCTIVE STRATEGIES

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

  2. 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

  3. Sexual reproduction needs a high energy input: • Two individuals needed • Mates have to find each other • Competition for mates occurs • Reproductive behaviour has to be coordinated • Producing offspring that will survive often requires parental care e.g. feeding and protection against predators The above are the reasons why reproductive strategies developed to ensure maximum reproductive success. Lorraine Kuun, July 2011

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

  5. 1. COURTSHIP • Simple strategies include pheromones (chemical), brightly coloured body parts (visual) and mating calls (auditory) stimuli. Lorraine Kuun, July 2011

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  7. Courtship • Complex strategies, unique to species, include courtship displays, annual rut (period of sexual excitement), lek breeding system, courtship-feeding. Lorraine Kuun, July 2011

  8. 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 Lorraine Kuun, July 2011

  9. Springbok compete for females during rutting season Lorraine Kuun, July 2011

  10. Timing of sexual display important • Females will be in peak condition to nurture developing baby. • Young are born when enough food is available to enable them to reach reproductive age. Lorraine Kuun, July 2011

  11. Territoriality – marking territory with urine and secretion from glands – no other male will enter area (also for feeding purposes) Lorraine Kuun, July 2011

  12. Lek breeding systems – groups of males gather to display and females select Above: male springbok display Left: male cichlids make bowers for females to lay eggs Lorraine Kuun, July 2011

  13. Male hoopoe feeds female; if she accepts, they will mate Lorraine Kuun, July 2011

  14. How will courtship behaviour maximise reproduction? • 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. Lorraine Kuun, July 2011

  15. 2. 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

  16. How does external fertilisation maximise reproduction? • Huge numbers of eggs increases probability of fertilisation. • Courtship rituals ensure that males and females are closer to each other. • Eggs of marine species release species-specific chemotactic factor to attract sperm. • Spawning is timed to occur when ocean currents can disperse eggs e.g. sessile species. • Young easily dispersed by sea currents; reduce competition. • No complicated physical mating, using energy. • Larval form gets food directly from environment; no energy input from parent. Lorraine Kuun, July 2011

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

  19. 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. • 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). Lorraine Kuun, July 2011

  20. How does internal fertilisation maximise reproduction? • Fertilisation is more certain – gametes placed closer together. Fewer gametes needed. • Energy saved in producing fewer gametes can be used for other purposes. Lorraine Kuun, July 2011

  21. Energy saved by internal fertilisation can be used for ... • Yolk to feed young. • Shells that enclose eggs (oviparity); better protection increases survival rate. • Some fertilised eggs very well-protected e.g. Sharks (ovoviviparity) and mammals (placenta). • Less wastage of gametes – in humans one egg per month produced. There is a disadvantage: a cooperative partner is needed! Lorraine Kuun, July 2011

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