Annual Reproductive Success = Fertilization Success X Offspring Survival
Male Female
Previous difficulty in assigning paternity
Previous work on mammalian male reproductive success
Large mammals
Pronounced sexual dimorphism (size and weaponry)
Harem polygyny
Variation in Reproductive Success:
• Lifetime: 0-24 calves (n=13)
• Annual: 50% of males sire 0 calves; <5% sire >4
• Exclusive territories• Minimal sexual dimorphism
(Male/Female mass ratio ~ 1.05-1.11)
• Asynchronous estrus
• Harem defense• Pronounced sexual
dimorphism (Male/Female mass ratio ~ 1.70)
Hypothesis
Reproductive success in male red squirrels will be unrelated to size.
Rather it will be driven by:
• Age
• Mobility
• Resource Availability
• Inbreeding Avoidance
The Players
• 74 Males and 57 Reproductive Females on 2 plots (KLOO and SUL)
• Seasonal OSR = 1.3
Methodology
• Radio-collared females• Behavioural monitoring
of mating chases– Time– Male/female behaviour– Male ID (attending and
copulating)
• Morphological measurements
• Data set– Age– Relatedness
Squirrel Mating at Kluane 2003
• February 19 - May 2
• 49 (usable) mating chases observed
• 0-3 Estrus bouts/day
• Number of males/chase
= 10.4 ± 2.4 (N = 19; Range = 6-14)
Mating Success
• Male– KLOO: 3.2 ± 2.3 copulations/male– SUL: 4.5 ± 2.6 copulations/male
• Female– KLOO: 5.9 ± 3.2 copulations/female– SUL: 8.5 ± 2.3 copulations/female
• Proportion of males in chase receiving a copulation = 0.77 ± 0.19 (N = 41)
Variation in copulatory success
024681012141618
0 1 2 3 4 5 6 7 8 9 10 11 12
Number of Copulations
Num
ber o
f Mal
es
Variation in chase attendance
024681012141618
0 1 2 3 4 5 6 7 8 9 10 11 12
Number of Copulations
Num
ber
of M
ales
CopulationChase
0
2
4
6
8
10
12
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Chases Attended
Cop
ulat
ions
Atta
ined
R2 = 0.7; P <.001
Hypothesis
Reproductive success in male red squirrels will be unrelated to size.
Rather it will be driven by:
• Age
• Mobility
• Resource Availability
• Inbreeding Avoidance
0
2
4
6
8
10
12
200 250 300
February Mass (g)
Num
ber
of C
opul
atio
ns
n/s
Hypothesis
Reproductive success in male red squirrels will be unrelated to size.
Rather it will be driven by:
• Age
• Mobility
• Resource Availability
• Inbreeding Avoidance
Hypothesis: Age will affect male reproductive success
Prediction: Older males will have a higher reproductive success than younger males
• Have more experience• Selected for by females• Higher quality genome• Confounding issues
Independent Variable: Age
Dependent Variable: Mating Success
Linear Increase Senescence Plateau
Age Distribution
• Mean Age = 3.8 ± 2.0 (N=44 ;Range 1-8)
02468101214161820
1 2 3 4 5 6 7 8
Age (yr)
Num
ber
of M
ales
02468
101214
0 1 2 3 4 5 6 7 8
Age (yr)
Num
ber
of C
opul
atio
ns
n/s
Tentative Conclusions
• Mating success largely unrelated to age or mass• Driven by reproductive effort• Factors affecting chase attendance
– Sex ratio of neighbours– Inbreeding avoidance– Energetics– Behavioural attributes (e.g exploration forays)
• Factors affecting fertilization success– Sperm competition– Behavioural attributes (e.g. mate guarding)
Future Directions
• Paternity (Coltman/Gunn)– Actual Reproductive Success– Relatedness (Inbreeding)– Sperm Competition
• Energetics (Humphries)– Costs of reproduction for males– Effect of resources
• Endocrinology (Boonstra)– Condition– Immunocompetence