Parents, offspring and helpers

1
Parents, offspring and helpers

• MSc ACSB 2005/06
• Session 13

2
Strategies

• Parental behaviour and life histories as
  strategies
• Sex change as a life-history strategy
• At 80 of maximum body size (Allsop West,
  2003, Nature 425, 783-784), this percentage
  invariant from shellfish to fish.
• Parental strategies breed independently or
  co-operate (e.g., with parents) as helper

3
Co-operative breeding in birds

• 3.2 of birds have helpers / co-operative
  breeding
• Not randomly spread - concentrated in 8 families
• Babblers, bee-eaters, fairy wrens, anis,
  scrubwrens/ thornbills, honey-eaters,
  tree-creepers, corvids
• Rare in 5 families
• Parrots, hummingbirds, pigeons, tyrannids, finches

4
Co-operative breeding (2)

• Increased co-operation linked to
• Low mortality, small clutches, stable tropical
  habitat, stable non-fluctuating environment
• Slow turnover few opportunities for independent
  breeding, helping an alternative route to
  reproductive success
• Co-operation probably results from a life history
  feature (low annual mortality)

5
Costs of parenting

• Willow tit lower survival after breeding the
  larger the number of young reared. Feeding young
  BMR increase equivalent to logging with a hand
  axe
• Red deer if the summer is poor ( wet), hinds
  survive less well when they have had a calf,
  especially if it survived 1st winter
• British aristocratic Fs who reach 80 yrs have
  50 probability of being childless
• If Rhesus monkeys previous offspring was a
  daughter, mother takes longer to become pregnant
  next time (daughters more costly)

6
Trivers PI theory

• Graphical model predicts a period of P-O conflict
  a natural consequence of conflict of interests.
  Young try to take what parent may not want to
  give
• Trivers Willard predict shifts in sex ratio so
  that optimal division between investment in M and
  in F offspring

7
PI when to feed an offspring?

• Does begging provide an honest signal of need?
• Kilner in birds such as canary, red flush
  intensifies with level of food deprivation
• Briskie begging louder in species with larger
  proportion of EPY relatedness to nest-mates
  lower, so costs of diverting next meal to self
  from them are reduced

8
Modelling the western bluebird

• Davis et al. (1999) PRSB 266, 1791-1797
• Simulations on web, and background
• http//www-abc.mpib-berlin.mpg.de/sim/Parental/Si
  mulation.html
• http//www-abc.mpib-berlin.mpg.de/sim/Parental/in
  dex.html

9
Understanding PI

• This set of 3 slides for background it will be
  skimmed in the class
• Modelling PI in birds
• What simple / complex rules are most effective
  for parents feeding young?
• Feed smallest, largest, hungriest, at random
• OR multiple cues? Look-ahead optimisation?
• Simple strategies good
• 0..30 food availability- Feed largest
• 30..70 - Feed smallest
• 70-80 - Feed hungriest

10
Understanding PI (2)

• Multiple cue strategies were refinements of the
  single strategy rules
• Cognitively complex optimising strategies less
  successful than single/multiple cue/random near
  sighted and egalitarian
• Todd Gigerenzer very simple rules work
• Resources scarce - save most viable young
  (despotic) resources plentiful - egalitarian

11
PI theory

• Parents should adjust investment in young to
  reflect costs and benefits
• Trivers-Willard Hypothesis Mothers differential
  treatment of M/F young will reflect
• her ability to invest, and the
• impact of this investment on offspring RS
• Variance in male RS much higher than female RS
• Mothers in good condition expected to produce
  more sons, those in poor condition expected to
  produce more daughters

12
PI in red deer on Rhum

• RS of male calves depends strongly on mothers
  rank
• RS of female calves unrelated to mothers rank
• Better for subordinate females to invest in
  daughters, and dominant females in sons
• Variation in birth sex ratio with rank
• Males 46.9 (low), 53.9 (mid), 60.6 (high)

13
Red deer sex ratios reflect mothers rank
Tim Clutton Brock, Red deer on Rhum
46.9 53.9
60.6 sons
14
American Opossum sex ratios

• Studied in Venezuela (Austad/Sunquist)
• Half pairs given sardine diet supplement
• Provisioned 75 (vs. 55) M-biased litters
• Bias visible very early, by 15 days age
• No difference in no. young, no inc. in mortality
• Provisioned pairs have heavier young
• Sons survive better if mothers provisioned,
  daughters show no difference
• So invest in the most beneficial way if
  provisioned

15
Sex ratio and culture

• Rajput families in Uttar Pradesh (Hrdy)
• C19 high caste families had no daughters
  extreme 400100 MF ratio
• Low-caste daughters can marry up, good
  connections son cant - may not marry at all
• Having a daughter is a blessing for the family
• High-caste daughter brings costs, son brings a
  dowry
• Caste linked to sex-specific inheritance (Bamshad
  et al. (1998) Nature 395, 651)
• Mitochondrial DNA (F line) - maternally-transmitte
  d traits widely distributed across castes
• Y chromosome traits (M line) are much more
  strongly localised in caste of origin

16
Human sex ratio biases

• Barrett et al. Hungarian gypsies
• F reproduce for longer if 1st child a daughter
• F have shorter interbirth interval if first child
  a daughter (compared to a son)
• 4th child at 8.6 yrs vs. 11.1 yrs
• Girls can marry up and attract greater investment
  by parents, especially in urban setting greater
  opportunity for hypergamy

17
Father-absent life histories

• Suggestion that growing females assess fathers
  PI (father absent/present) and use it to predict
  what resources will be like when they grow up
• If present, they look for reproductive partners
  who will provide resources for their shared
  offspring
• If absent, they switch to life-history path with
  early sexual maturity plus an opportunistic /
  mistrustful relationship style, and use their
  sexuality to get men to offer resources
• Quinlan (2003) Evol. Hum. Behav. 24, 376
  Thornhill Furlow (1998) Adv. Study Behav. 27,
  319

18
Father-absent (2)

• Quinlan 10, 847 US women, 74 with both parents
  throughout 18 years.
• Early separation (0..6 yr) increased hazard
  (risk) for X by Y compared to intact families
• Early menarche (1.8 times)
• Early first intercourse ( 4 times)
• Early first pregnancy (2.5 times)
• Later separations, similar but smaller effects

19
Father-absent (3)

• 1-2 changes in care-taking situation gave no
  significant increase in risk
• 3() changes enhance risk of
• Early menarche
• Early first intercourse (4 times)
• Early first pregnancy (5 times)
• Live with 1 parent (M or F) only from below 6 yrs
  -gt earlier menarche. Stepfathers presence does
  not eliminate effect of fathers absence

20
References

• Quinlan (2003) Evol. Hum. Behav., 24, 376-390
• Trivers (1985) Social Evolution. Chapter 7, 10.
• Thornhill Furlow (1998) Adv. Study of
  Behaviour, 27, 319-369