Parental Investment “any characteristics or actions of parents that increase the fitness of...
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Parental Investment “any characteristics or actions of parents that increase the fitness of offspring at a cost…to the parent’s fitness” Clutton-Brock 1991
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Parental Investment
“any characteristics or actions of parents that increase the fitness of
offspring at a cost…to the parent’s fitness”
Clutton-Brock 1991
Territory Bequeathal
Mother gives part or all of her territory to her offspring
•stops defending territory•becomes vagrant•shows up on vacant middens•offspring take over midden
Why Bequeath?
•Parental Investment?
Alternatives:•Improve territory quality•Parent-Offspring conflict
Longterm Evidence
• 9 years (89-97)• 2835 tagged individuals • 1013 litters• 590 litters with young to
weaning• Post-breeding behaviour for
485 litters (302 females)
Analyses by Dominique Berteaux
Post-breeding Options
Keep Share Bequeath
Increasing investment
0
10
20
30
40
50
Keep
%
Proportion using each behavioural strategy
Share Bequeath
n = 214
n = 71
n = 200
0
20
40
60
80
% s
urv
ivo
rsh
ip
Owned another territory
Did not ownany territory
Owned their mother’s territory
Effect of territory ownership on juvenile overwinter survival
n = 186
n = 288n = 206
Costs/Benefits to Females
Survive 70.4 69 57.7Reproduce 80 79.6 80.5Litter size 2.73 1.1 2.87 1.3 2.70 1.2
# Weaned .98 1.0 1.54 1.2 1.09 1.1
Keep Share Bequeath
Subsample of keep,sharen=30-70
Who Bequeaths?
Can this be predicted by parental investment
theory?
Factors affecting whether femalesbequeathed or not
0
2.5
5
Age
No Yes
0
50
100
150Cone production
No Yes
01234# of juveniles
No Yes
0
50
100
150Cone reserves
No Yes
Parental Investment Theory
Predictions Red Squirrels
Increase: With age yesWith # weaned yesWith food yesIn sex with >return no
Which Juveniles obtained middens from
their mother?
0
20
40
60
Daughters Sons
P<0.009
n=411
Experimental Evidence
• Permanent and temporary removal of neighbours in late summer
• Monitor takeovers– attempts– successes
Design:
Who took over removal territories?
0
0.2
0.4
0.6
Mothers NBF J uvs
Population Take- overs
P=0.021
Mothers with offspring
Parental investment Pre-lactation?
Do females acquire middens as a form of parental investment?
Do females acquire middens as a form of parental investment?
Experiment
• Experimental removal of neighbouring males in October
• 8 Experienced (had produced young)8 Inexperienced (no young)
• Monitored fates of vacant middens
Results
No females switched territoriesbut some acquired a second midden
OctoberX
X
April
X
X
6 of 7 Experienced1 of 6 Inexperienced
Results
Acquired second midden 61
Weaned young 54
Gave midden to offspring 51
Variable Exp Inexp
Why Experienced Females?
Breeders First-time Breeders
Probability of breeding 100% 7-100%next year
Conclusion
Female red squirrels acquire middens well in advance of mating
or offspring dependency and
relinquish these to their offspring
Anticipatory Parental
Investment
Bequeathal
Unanswered Questions:• Proximate cues
– Availability of vacant middens– Resources on and off territory
• Anticipation – is it real• The male-female thing• Heritability of bequeathal
behaviour
