(a) Parental investment

• Comparison of sperm and egg production in relation to number and energy store

• Greater investment by females

  • Female investment in the egg structure in non-mammals or in the uterus and during gestation in mammals.

• Parental investment is costly but increases the probability of production and survival of young

• Classification of r-selected (r-strategists) and K-selected (K-strategists) organisms based on level of parental investment in offspring and number of offspring produced

  • Characteristics of r-selected species: smaller; have a shorter generation time; mature more rapidly; reproduce earlier in their lifetime, often only once; produce a larger number of smaller offspring, each of which receives only a smaller energy input; limited parental care; most offspring will not reach adulthood.

  • Characteristics of K-selected species: larger and live longer; mature more slowly; can reproduce many times in their lifetime; produce relatively few, larger offspring; high level of parental care; many offspring have a high probability of surviving to adulthood.

• r-selection tends to occur in unstable environments where the species has not reached its reproductive capacity, whereas K-selection tends to occur in stable environments

• Comparison of costs and benefits of external and internal fertilisation

External fertilisation

• • benefits: very large numbers of offspring can be produced

  • costs: many gametes predated or not fertilised; no or limited parental care; few offspring survive

Internal fertilisation

• • benefits: increased chance of successful fertilisation; fewer eggs needed; offspring can be retained internally for protection and/or development; higher offspring survival rate

  • costs: a mate must be located, which requires energy expenditure; requires direct transfer of gametes from one partner to another

(b) Reproductive behaviours and mating systems in animals

• Mating systems are based on how many mates an individual has during one breeding season

• These range from polygamy (polygyny and polyandry) to monogamy

  • Monogamy: the mating of a pair of animals to the exclusion of all others.

  • Polygamy: individuals of one sex have more than one mate.

  • Polygyny: one male mates exclusively with a group of females.

  • Polyandry: one female mates with a number of males in the same breeding season.

• Many animals have mate-selection courtship rituals

• Courtship in the field: create an ethogram observing the ritualised courtship displays of water birds, such as grebes or ducks.

• Successful courtship behaviour in birds and fish can be a result of species-specific sign stimuli and fixed action pattern responses

• Sexual selection selects for characteristics that have little survival benefit for the individual, but increase their chances of mating

• Courtship in the laboratory: observe stickleback or Drosophila courtship; investigate sexual selection in different Drosophila varieties.

• Many species exhibit sexual dimorphism as a product of sexual selection

  • Females are generally inconspicuous; males usually have more conspicuous markings, structures and behaviours.

• Reversed sexual dimorphism occurs in some species

• Female choice involves females assessing honest signals of the fitness of males

  • Honest signals can indicate favourable alleles that increase the chances of survival of offspring (fitness) or a low parasite burden suggesting a healthy individual.

• In lekking species, males gather to display at a lek, where female choice occurs

  • Some bird species exhibit lekking behaviour. 

  • Dominant males occupy the centre of the lek, with subordinates and juveniles at the fringes as ‘satellite’ males. 

  • During the display, female choice occurs.

• Success in male-male rivalry through conflict (real or ritualised), increases access to females for mating

  • Males will fight for dominance and access to females, often using elaborate ‘weapons’ such as antlers, tusks, horns.