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7 - Socio biology Mate selection - Coggle Diagram
7 - Socio biology Mate selection
Battle of sexes - Dawkins 1976
reproductive strategies should be sensitive to natural selection
research shows strong genetic contribution to reproduction in all animals
all living things are offspring to the successful animals in the evolutionary game
Reproductive decisions
Barash (1982) - 4 reproductive decisions faced by living things
2 - When?
2 components
at what age? - the earliest age you can be to produce maximum amount of offspring
what time of the year? - produce offspring when food is most available
3 - With whom?
courtship = sexually reproducing species select males
behaviour patterns for courtship are vivid, stereotyped and species specific
characteristics have a strong genetic control
mistakes in mate selection can be very costly
1 - How?
sexual reproduction is very costly
exposure to danger
desertion and cuckoldry
time and energy
genetic cost (parents only 50% related to offspring)
Benefits must outweigh costs
benefit is producing genetically diverse offspring so they can stay in the game
makes sure the behavioural strategy evolves
4 - What social system?
Reproductive isolating mechanisms - Dewsbury 1987
mistakes in mate selection prevented by 3 mechanisms designed to reproductively isolate species
Mating - related mechanisms (genitalia compatibility)
Post - mating mechanisms (endocrine - hormonal events necessary for fertilisation) - least effective
pre - mating mechanisms (courtship) - most effective as is immediate
anisogamy
Female - small number of large gametes (ova)
Male - large number of small gametes (sperm)
definition = differential gametes (sex cell) production
Investment differential
errors in mate selection are more serious for females as they have more to loose = why they are the selectors
Males only really provide genetic material = low investment
females invest more
courtship
courtship communication
is the ability to
2 - Select (receive and act upon the signals) FEMALE - SALES RESISTANCE
1 - advertise (transmit unambigious signals). MALE - SALESMANSHIP
4 functions
2 - overcoming fear of close contact
3 - maintenance of bond
1 - Attraction
4 - evaluation of potential mates
ethology - first 3
sociobiology added 4th function
assessment of physical prowess (will they protect the female and land? Physical features such as antler size)
assessment of availability for parental duties
Mate attractiveness
Male widow birds
Longer tails is more attractive (shown by more nests per male)
Peacocks
strong positive correlation between number of eyespots on males tail and number of mates attracted
Zebra Finch
males with artificial head plumes were much more attractive to females
Pehans
females most interested in the lower edge of the tail fan (used eye tracking technology on females)
sexual selection - Darwin
Dimorphism = 2 forms. In this case male-female differences in appearance and behaviour
Intrasexual selection
competition between males for territory and females
Favours increased size, weaponry and aggression
2 types of natural selection responsible for sexual dimorphisms and both operate on the male
Intersexual selection
competition between males for the attention of females
leads to elaboration of male appearance and behaviour linked to courtship
Why does it operate on the male?
females invest more in offspring
females are a vital resource for males so compete for access to them
Critical test = investment reversal
cuckoldry
definition = males helping rear another males offspring as the women mated with someone else
strategies to avoid it
refusing to mate with females already suspected of mating already
protection of pregnant females (guarding, mating plugs, repellents)
problem for males - should avoid it
Parental investment
reversal of parental investment
female seahorses are larger and more aggressive than males
female jacana (bird) when they get a new male, they destroy all the eggs currently being incubated by the male = female infanticide
implications of inequality of PI
benefit of reproduction = number of offspring produced by the pair
maximum net productive success is achieved with fewer offspring for women (not same for men) - explains menopause in women and promiscuity in men
relationship between the benefit of reproduction and costs to each.
net productive success = maximum difference between benefit and cost)
Trivers (1972) theory of parental investment
PI = any behaviour towards offspring that increases its chance of survival at the cost of parents ability to invest in future offspring
it has some interesting consequences
Mating systems
3 basic mating systems
polygamy (polygyny - one male with lots of females and polyandry - one female with lots of males)
Promiscuity = no bonds formed - females breed with best males and rear offpring solo creating lek species
monogamy (least common) = pair bonds formed
advantage to who?
dominant males - polygynous and promiscuous is advantageous
female advantage - gain fitness for their offspring due to genetic combination by choosing the best male and getting resources from them
subordinate males - inclusive fitness (assisting dominant brothers), deferred fitness (wait till next year) and sneak copulations
Humans - only 3% of mammals are monogamous and this is only recent development (used to be polygynous)