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Sex Ratios II
Terms in this set (18)
What facultative responses are there where a mother would adjust the ratio of offspring sex
Local mate competition
Local sex ration
Absence of helpers
What would a female do to exploit the local sex ratio if the population is not at the ESS?
produce rarer sex
What evidence is there of local sex ratio exploitation?
- many females killed as control strategy
- surviving female produced more daughters
(Also Triver "Social Evolution" - after both world wars, male-biased sex ratio), possible condition dependent effect.
Trivers and Willard, 1973
Mothers should base their sex ration on their condition
What three assumptions do Trivers & Willard, 1973 assume?
That condition of young after investment depends on condition of mother
Condition of young after investment influences their adult reproductive success
Assumed that males gain more improved condition
Clutter-Brock, Isle of Rhum
Dominance females were in better condition
- breed earlier, live longer
- higher lifetime reproductive success
- stronger effect of rank on sons
Dominant females produce more sons than daughter
In Cape mountain zebras rank has a stronger effect on?
high rank mothers have ?
- so makes sense to produce sons if low rank and daughter if high rank
high rank daughters
In Rhesus macaques:
Dominant females better at protecting daughters from harassment
dominant females have ?
dominant daughters: produce more dominant daughters
In what species does season (as affecting mothers condition) influence sex ratios?
Birds of prey
why are more sons produced earlier in the year?
Seal species are constrained by how long they can suckle
early in the season, pups have longer to suckle
In Kestrels why is there male bias early in the season and female late?
the probability of breeding as yearlong decreases with birth date in males
females probability is constant
model predicts decrease in % sons with time in season
What species is Host size a determinant for sex ratio?
Parasitic wasps with 1 egg per host
- females gains more than male form being large
- males tend to be produced from small hosts
- females form large hosts
good experimental evidence of this
Across parasitoid species when are you more likely to see an effect?
if parasitoid kills or paralyses host
host cannot grow, so size known.
Who showed helpers can affect sex ratios?
Komdeur et al, 1997
- helpers on poor territories reduce success of parents
- 1 or 2 helpers good (helpers mainly female)
Komdeur et al, 1997 did a study on?
Trivers-Willard very influential but?
hard to test
Fisher is concerned with?
population sex ratios
facultative is when ?
individuals adjust sex ratio
THIS SET IS OFTEN IN FOLDERS WITH...
Size & Fat
Cost of reproduction
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