Reproductive strategies for Survival

VCE Biology – Unit 2

Reproductive strategies are structural, functional and behavioural adaptations that improve the chances of fertilization and/or

increase the survival rate of offspring.

Asexual Reproduction Sexual Reproduction

No genetic differences Random gamete formation and combination allows genetic

variation

Simple and easy – no need to find a mate

Must find a suitable partner –time and effort

Little energy expended More energy required

Good strategy when environmental conditions are

favourable

Good strategy when environmental conditions are

variable

External versus Internal fertilisation

Male gametes are small, fragile and prone to dehydration. Aquatic organisms are able to disperse their gametes in the water around them. Terrestrial

organisms require alternative methods to ensure viable sperm is able to fertilize the egg.

Broadcast Spawning: Reef fish that gather together and release their eggs and sperm simultaneously into the water – these eggs are termed ‘pelagic’, or free-floating. (eg. Boxfish, abalone and coral)

Demersal Spawning: Fish that lay eggs together in a type of ‘nest’ (a hollow in the sand or a crevice in rocks) which are then fertilised by the males are demersal spawners. They produce larger and fewer eggs than broadcast spawners, because energy is needed to guard and clean the eggs. (eg. Anenome fish)

Monogamy – More than 90% of bird species are monogamous, that is, they form pairs for one or more breeding seasons. Eg. Eagles, albatross and brolgas. These species are more likely to have altricialdevelopment (require significant parental care).

Polygamy –polygyny (one male, many females)Polyandry (one female, many males)

Promiscuous – males and females in a social group engage in multiple and indiscriminate mating.

R-selection (Quick and many Eg. Mice and rabbits)

K-selection (slow and few Eg. Elephants, whales, humans)

Oviparity

Oviparous animals lay hard-shelled eggs that act as a ‘pond’ for the developing embryo.

Vivaparity – Live birth

Placental mammals (Eutherian) –Eg. humans, cats, dogs, sheep and cows).

Marsupials (kangaroos, possums, wombats and Koalas)

Monotremes (Echidna and Platypus)

Primitive mammals that lay soft-shelled eggs.