Sex and Behaviour

Question 1

What are mating systems?

Answer 1

• Mating systems are based on how many mates an individual has during one breeding season.
• These range from polygamy to monogamy.

Question 2

Describe polygamy

Answer 2

• 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.

Question 3

Describe species-specific sign stimuli and fixed action pattern responses.

Answer 3

• Animals use signals that only members of the same species understand.
• These may include giving off chemicals, or making sounds or certain displays to initiate mating.
• This means that individuals mate when most fertile, increasing the chance of successful reproduction.
• These signs and signals will be innate, thus instinctive.

Question 4

Describe sexual dimorphism.

Answer 4

• Many species exhibit sexual dimorphism as a product of sexual selection.
• Any physical differences between males and females.
• Often expressed as differences in size.
• Most of the time the male has conspicuous markings, structures and behaviours and the female is more inconspicuous (increasing her and her offspring’s chance of survival).

Question 5

Describe reversed sexual dimorphism.

Answer 5

• In some species, the female is more conspicuous than the male.
• Smaller males are found in species which have to travel long distances for females. Smaller size is better for speed and stealth.

Question 6

Describe female choice.

Answer 6

• 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.

Question 7

Describe lekking.

Answer 7

• In a number of bird and insect species, males display communally in a small area = a lek.
• Females visit the lek and assess whether signals are honest and are really a sign of male fitness (female choice).
• They will look for good condition and low parasite density, both implied by a healthy plumage.
• Dominant males occupy the centre of the lek, with subordinates and juveniles at the fringes as ‘satellite’ males.

Question 8

Describe male-male rivalry

Answer 8

• 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.
• Elaborate ‘weapons’ such as antlers, tusks, horns are often used.

Question 9

Describe parental investment.

Answer 9

• In animals, sperm are produced in larger numbers compared to eggs.
• Due to the presence of an energy store, eggs are much larger and fewer in number.
• A greater investment is made by females (egg structure in non-mammals or in the uterus/during gestation in mammals)
• Their chance of reproductive success is lower and the chance of passing on genes is reduced.

Question 10

What is the advantage of external fertilisation?

Answer 10

Very large numbers of offspring can be produced.

Question 11

What are the disadvantages of external fertilisation?

Answer 11

• Many gametes predated or not fertilised;
• No or limited parental care;
• Few offspring survive.

Question 12

What are the advantages of internal fertilisation?

Answer 12

• Increased chance of successful fertilisation;
• Fewer eggs needed;
• Offspring can be retained internally for protection and/or development;
• Higher offspring survival rate.

Question 13

What are the disadvantages of internal fertilisation?

Answer 13

• A mate must be located (requires energy expenditure);
• Requires direct transfer of gametes from one partner to another.

Question 14

Describe parental care.

Answer 14

• Parental investment is costly but increases the probability of production and survival of young.
• The level of parental care depends on the number of offspring and the environment.
• Stable environment = smaller number but more investment and parental care.
• Unstable environment = many offspring with lower investment and parental care.

Question 15

Describe r-selected populations.

Answer 15

• unstable environment
• short maturation time
• high death rate
• many offspring produced per reproductive episode
• one reproduction per lifetime
• first reproduction early in life
• small offspring/eggs
• no/limited parental care

Question 16

Describe k-selected populations.

Answer 16

• stable environment
• long maturation time
• low death rate
• few offspring produced per reproductive episode
• many reproductions per lifetime
• first reproduction later in life
• large offspring/eggs
• often extensive parental care