Sex & Behaviour Flashcards
Parental investment is costly but…
increases the probability of production and survival of young and therefore the evolutionary fitness of the parent
Description of female gametes (eggs)
Large, nutrient filled, expensive to produce, limited number and produced infrequently
Description of male gametes (sperm)
Small, no nutrients, cheap to produce, constantly made throughout life
What is the clearest sexual dimorphism amongst vertebrates?
Gamete size, this physical sex difference explains behavioural differences
How is there a greater investment by females?
In individual egg structures and also in the uterus during gestation in mammals
What is external fertilisation?
When the gametes are releases directly into the environmente.g. fish, crabs
Benefits of external fertilisation
Very large numbers of offspring can be produced
Costs of external fertilisation
Many gametes predated on or not fertilised
No/limited parental care
Few offspring survive to reproductive age
What is internal fertilisation?
When the gametes are releases into the reproductive tract of the female
e.g. humans, chimpanzees
Benefits of internal fertilisation
Increased chance of successful fertilisation
Fewer eggs needed
Offspring can be retained internally for protection and/or development
Higher offspring survival rate
Costs of internal fertilisation
Mate must be located which requires expenditure of energy
Requires direct transfer of gametes from one partner to another
R-selected and K-selected is a classification of organisms based on…
the level of parental investment and number of offspring produced
R-strategists use…
External fertilisation e.g. fish, crabs, insects
K-strategists use…
Internal fertilisation e.g. humans, chimps, elephants
Characteristics of R-selected organisms
Smaller and shorter generation time
Mature more rapidly
Reproduce earlier in lifetime (often only once)
Produce large number of smaller offspring
Offspring receive small energy input as there is limited parental care
Most offspring will not reach adulthood therefore do not reproduce
Characteristics of K-selected organisms
Larger and live longer
Mature more slowly
Reproduce many times in lifetime
Produce relatively few larger offspring
High level of parental care
Many offspring have a high probability of surviving to adulthood and therefore reproducing
R-selected tend to occur in…
Unstable environments where the species has not reached its reproductive capacity
K-selected tend to occur in…
Stable environments
What are mating systems based on?
How many mates an individual has during one breeding season
What is monogamy?
The mating of a pair of animals to the exclusion of all others e.g. humans, albatross
What is polygamy?
When individuals of one sex have more than one mate
What are the two types of polygamy?
Polygyny- one male mates exclusively with a group of females e.g. stag, elephant seal
Polyandry- one female mates with a number of males during the same breeding season
Courtship involves…
Behaviours and characteristics associated with mate selection
Successful courtship behaviour in… can be a result of…
Birds and fish, species-specific sign-stimuli and fixed action pattern responses
What are fixed action pattern responses?
Instinctive and vary little between member of the same species
What is shown by many birds and fish?
Ritualised courtship behaviours
Sexual selection selects for…
Characteristic that have little survival benefit but increase chances of mating
Many species exhibit… as a product of sexual selection
Sexual dimorphism (reversed occurs in some species)
Males usually have more conspicuous…
Markings, structures and behaviours than females
What is female choice?
When females assess honest signals for fitness of males
Honest signals indicate…
Favourable alleles that increase chances of offspring survival (fitness) or low parasite burden (healthy individual)
In lekking species…
Males gather at a lek where female choice occurs
e.g. bird species where dominant males occupy the centre of the lek with subordinates and juveniles at the fringes as ‘satellite’ males
What happens during male-male rivalry?
Males fight for dominance and access to females using elaborate weapons (antlers, tusks, horns)
Success in male-male rivalry…
increases access to females for mating
