2.4 Flashcards
Explain sexual dimorphism in vertebrate gametes…
in female gametes, large nutrient filled energy store, expensive to produce, limited number, produced infrequently, if fertilised leads to high cost for female
in male gametes, small, non nutrients, cheap production, constantly made throughout life
What is internal fertilisation?
process by which sperm and egg nuclei fuse inside the female
What is external fertilisation?
when fusion occurs outside the female
How does external fertilisation work?
large number of eggs/sperm released into water and fertilise in absence of parents, external water essential to prevent gametes drying and to provide medium for sperm
Why is courtship behaviour important in external fertilisation?
as timing is crucial to ensure mature sperm/ripe eggs meet
Why is environmental stimuli important in external fertilisation?
i.e. temperature or day length may cause individuals to release gametes at the same time
How can chemical signs be used in external fertilisation?
chemical signs from one individual releasing gametes may trigger gamete release in others
Explain internal fertilisation…
necessary where no external moisture is available
cooperative behaviour ultimately leads to sexual intercourse
requires highly advanced reproductive systems
What are the costs/benefits of internal fertilisation?
benefits
- increased chance of success
- fewer eggs needed
- offspring retained internally for protection/development
- higher offspring survival rate
costs
- mate must be located, requires energy
- requires direct transfer of gametes from one partner to another
What are the costs/benefits of external fertilisation?
benefits
- large number of offspring can be produced
costs
- many gametes predated or not fertilised
- no or limited parental care
- few offspring survive
Explain parental investment benefit and female costs…
- parental investment costly by increase probability of production and survival of young
- most animals, female give more parental investment than just an egg
What are female costs in mammals and non-mammals?
mammals
- uterus prolonged internal gestation
-lactation
non-mammals
- egg structure with food store
What is the r/k selection theory?
relates to selection of combinations of traits in an organism that depend on quantity and quality of offspring
What is r-selection?
the species focuses on increased quantity of offspring at expense of parental investment individually
What is k-selection?
reduced quantity of offspring corresponding with increased parental investment
When does r-selection tend to occur?
when environments are unstable where species not reached reproductive capacity
When does k-selection tend to occur?
in stable environments
What are characteristics of r species?
- smaller
- shorter generation time
- rapid maturing
- reproduce earlier in lifetime
- limited parental care
- most offspring do not reach adulthood
- e.g. mice, rabbits, insects, cane toads, octopus, mass spawning organisms
What are characteristics of k species?
- larger
- live longer
- mature more slowly
- reproduce many times
- relatively few larger offspring
- high level of parental care
- high probability of reaching adulthood
- e.g. humans, humpback whale, elephants, some birds
What are mating systems based on?
how many mates an individual has during one breeding season
What is monogamy?
mating of a pair of animals in exclusion of all others
What is polygamy?
individuals of one sex have more than one mate
What is polygyny?
one male with multiple females
What is polyandry?
one female with a number of males in the same season
Give an example of monogamy…
most birds due to high parental care in feeding chicks, unlikely one parent could handle feeding and protecting alone
Give an example of polygamy…
In mammals, female is often only food source fore young (milk), males role is to protect, therefore polygamy common with one male mating with multiple females in harem
Why is the female reproductive strategy important?
there is much to lose if they choose the wrong male so they are selective with who they mate with
What are certain criteria for females in mating?
physical features
- e.g. size, strength confer to dominance so better resources
behavioural features
- e.g. indicates willingness to invest, good parenting
What do females do get alpha males?
they compete with other females
What do females look for when searching for a male?
they gain little from multiple matings so search for quality not quantity, almost every reproductively capable female will find a mate
What is the male reproductive strategy?
far less choosy, little to lose, everything to gain, get as many mating opportunities as possible, seek quantity and prefer superior female but are not choosy
What is male reproductive success?
males compete vigorously with other males for access to fertile females, but success is very variable and a small number of males achieve many mating with many never mating at all
Describe sexual dimorphism…
females generally have inconspicuous markings
males have more conspicuous markings, structures and behaviours resulting in males with:
- larger body size
- evolution of weapons in males for fighting other males for mate
- evolution of dramatic colours
- displays for courtship
can be reversed for some species
When are males often smaller?
in species that travel long distances to find mates, smaller size advantage for speed and stealth
Describe sexual dimorphism in angler fish…
- display extreme dimorphism as males live an almost parasitic existence with and underdeveloped digestive system
- upon finding mate, male fuses to female as a parasitic existence, taking more than just giving sperm
What is male-male rivalry?
competition/rivalry sometimes determines which animals mate; fight for dominance, female access often using elaborate weapons; success through conflict (real or ritualised) increases access to females
What are sneaker males? (satellite males)
some males successful as ‘sneakers’, strategy in which smaller males can access female partners avoiding altercations with dominant males
- e.g. cuttlefish males
What does female choice involve?
involves females assessing ‘honest’ signals of male fitness, signals which don’t mislead a female into thinking he’s fitter than he actually is
What do honest signals indicate?
favourable alleles to increase offspring fitness or low parasitic burden
What do dishonest signals do?
they can be disruptive for population, reducing sexual signalling system effectiveness
Explain the measuring of fitness?
measured or describe in terms of good genes and low parasite burden
fewer parasites suggest overall fitter population, less susceptible to infection
What is lekking?
exhibited in some bird species
- males gather to display a lek where female choice occurs, there are both dominant and satellite males
How are dominant males spotted in a lek?
dominant males occupy the centre, others around the edges
dominant males may be larger, have more vivid colouration or more elaborate displays
What can successful courtship behaviour be a result of?
in birds and fish, could be due to species specific stimuli and fixed action pattern responses
What are species specific stimuli?
may include giving off chemicals or making sounds or certain displays to stimulate mating
What is a fixed action pattern?
instinctive behaviour occurring across majority of species, often seen during mating rituals
Describe specific sign stimulus and FAPs in stickleback fish…
- female presents swollen belly to male (SS)
- male performs ‘zig zag’ dance (FAP and SS)
- female follows male (FAP and SS)
- male indicates nest to female (FAP and SS)
- female lays eggs (response)
